'A -r I -- 5 S P w w. r CONTENTS Page INTRODUCTION ..... .....--------------------------------------- The Nature of Peanut Leafspot Disease Disease Control ---..-------------THE EFFECTS OF FUNGICIDES 4 ---------------- 4 .----------___ ---5 Tolerance of Leafspot Fungi to Benlate ----------------- 9 Effects on Kernel Quality and Crop Value 11 Fungicide Effects on White Mold (Sclerotium rolfsii) 13 The Relationship between Leaf Loss and Yield 17 Fungicide Effects on Foliar-feeding Insects-----------17 __ __-21 EFFECT OF KYLAR ON PEANUT YIELDS THE ROLE OF SULFUR IN LEAFSPOT CONTROL SPRAY EQUIPMENT AND DELIVERY RATES --------24 --. PERFORMANCE 23 24 26 26 31 32 Methods of Application of Leafspot Fungicides Delivery Rates for Ground Sprayers IMPROVEMENT OF BRAVO (CHLOROTHALONIL) WET WEATHER AT HARVEST: WHEN Do You DIG? SUMMARY .........------------- REFERENCES -------------.- -33 APPENDIX 1.......................---------------------------------------35 List of Trade, Chemical, and Common Names for Fungicides in T ext --- -------------.- - -- --------- - ------- 35 APPENDIX 2 .----------------------------------------------------. Leafspot Disease Control Recommendations APPENDIX 3 ............ ..... 37 (1977) ------- 37 .. ..---------------------------------------38 -- -- Contributions of Plant Pathology to Peanut Production 38 FIRST PRINTING 5M, JUNE 1977 Information contained herein is available to all without regard to race, color, or national origin. Peanut Leafspot Research in Alabama 1970-1976' P. A. BACKMAN, R. RODRIGUEZ-KABANA, J. M. HAMMOND, E. M. CLARK, J. A. LYLE, H. W. IVEY II, and J. G. STARLING2 INTRODUCTION PEANUT PRODUCTION in Alabama began as the boll weevil wiped out the cotton crop in the early part of this century. Almost from the outset the peanut was afflicted with spotted leaves that were often accepted as the nature of the plant. By the late 1930's experiments were begun using sulfur dust for leafspot control, and later copper-sulfur dusts were used. Leaf- HISTORICALLY, spot was not effectively controlled, but these dusts delayed severe phases of the disease, which resulted in increased yields. More effective control was achieved in the early 1960's following the introduction of organic fungicides and more sophisticated spray equipment. It was not until the introduction of Benlate3 and Bravo in 1970 that leafspot was controlled to a point where little yield loss occurred as a result of leafspot infection. 1 This bulletin summarizes 7 years of research on the control of peanut leafspot, under a project supported by Auburn University Agricultural Experiment Station, the Alabama Peanut Producer's Association, and grants from chemical companies. The primary project, begun in 1972, had major objectives of (1) determination of chemicals most effective in control of the leafspot complex; (2) evaluation of the effects of leafspot fungicides on non-target organisms, particularly white mold (Sclerotium rolfsii Sacc.); and (3) development of systems for reducing the number of spray applications necessary for leafspot control. Trade names for chemicals are used for clarity; however, mention of a trademark or proprietary product neither constitutes a guarantee or warranty of the product nor implies its approval to the exclusion of other products that may also be available. 2 Associate Professor, Professor, Research Associate, Associate Professor, and Professor and Head, Department of Botany and Microbiology; and Assistant Superintendent and Superintendent, Wiregrass Substation. 3 Common and chemical names of all chemicals referred to in this bulletin can be found in Appendix 1. 4 ALABAMA AGRICULTURAL EXPERIMENT STATION The Nature of Peanut Leafspot Disease An understanding of peanut leafspot is necessary to understand disease research findings. Peanut leafspot may be caused by either of two fungi that occur wherever peanuts are grown. The most common of the two in the Southeastern United States is Cercospora arachidicola Hori, which causes early leafspot. Symptoms of this fungus are brown to dark brown circular spots usually surrounded by a yellow halo (see cover photo). Spore production typically occurs on the upper surface. Late leafspot, caused by Cercosporidium personatum (Berk. 8c Curt.) Deight., occurs later in the season and is usually darker on the lower surface of the leaflet than early leafspot. The lesion typically has a pimply lower surface with a less distinct halo than early leafspot. The disease cycle of Cercospora leafspot in the field is not completely understood, but typically follows this pattern: (1) spores are produced during periods of moisture (dew) on mature lesions; (2) the spores are released when the lesion dries and are windborne to young peanut leaflets; (3) during the next period of moisture the spores are activated, requiring 14-16 hours at 72°F to germinate and complete the infection process (if this time period is interrupted by a period of dryness the spores are killed; (4) 10-14 days after infection thie first symptoms of infection are visible; and (5) the mature sporulating lesion develops 16-20 days after infection. Late leafspot seems to follow the same sequence, but is somewhat slower in developing. Disease Control The disease cycle can greatly influence short-term results with field-applied fungicides. For example, if a 100 percent effective contact fungicide existed, and it was applied after infection had occurred, a period of 10-12 days would elapse before any disease reduction could be visible. This time lapse between treatment and response occurs because contact fungicides are effective only on spores or germination tubes on the leaf surface; they have no activity on established infections beneath the leaf cuticle. The establishment of control, therefore, must be developed on a preventative basis. The most desirable fungicides are those that possess both contact and systemic activity (15). Systemic fungicides not only kill fungal spores on the leaf surface, but can eradicate PEANUT LEAFSPOT RESEARCH IN ALABAMA 5 already established infections within the leaf. Unfortunately, none of these fungicides is presently available to peanut farmers for leafspot control. Understanding the disease cycle can allow flexibility in establishing spray intervals. During dry periods (when moisture periods do not exceed 12-14 hours), spray intervals can be extended. Conversely, intervals should be shortened during periods of extended moisture that frequently occur with rain or ground fog. The data presented in this bulletin deal primarily with the effect of the new high-performance fungicides, not only on leafspot but also on the quality of yield, insects, other diseases, and general plant health. In addition, attempts have been made to achieve control with reduced numbers of applications or reduced quantities of fungicide per acre. THE EFFECTS OF FUNGICIDES From 1971 through 1975 the primary fungicides recommended for leafspot disease control were: Benlate 50WP, 6 ounces per acre (through 1973); Bravo 75WP or 6F, 11/2 pounds per acre or 11/ pints per acre; Kocide 404S F, 2 quarts per acre; and Duter 47WP, 6 ounces per acre. Peanuts were grown in a Dothan sandy loam soil in a 1-year rotation with corn (Zea mays L.). Plot size was either 150 x 24 feet (1971-72) or 50 x 24 feet. Fungicides were applied every 14 days beginning 40-50 days after planting and ending 14-20 days before harvest. All fungicides were applied by a conventional ground sprayer calibrated to deliver 15 gallons per acre at 80 pounds per square inch. Peanuts were harvested three TABLE 1. PERCENT INFECTION OF FLORUNNER PEANUTS BY Cercospora AND Cercosporidium FOLLOWING TREATMENT WITH FOLIAR FUNGICIDES Percent infection Treatment 1971 1972 85.7 a 8.8 c 7.4 c 1973 1974 Meant Control Duter 47WP 97.2 a 64.8 a 16.1 c 20.9 c 92.9 a 24.7 c 88.62a 87.0 a 36.0 c 25.8 d Bravo 6F .. _......56.1 c _ Benlate 50WP ..... 40.5 d -... 60.7 c 75.9 b 29.4 b 25.4 b 26.5 b 12.2 c 51.7 b 55.9 b 45.4 b 40.2 bc Kocide 404S Fa3.. Values within columns followed by the same letter are not significantly different at the 5 percent level using Duncan's Multiple Range Test. 1 Mean weighted for number of replications in each year's test. 2 Resistance to Benlate developed in Cercospora during the 1973-74 seasons. 3 Cu[OH]2 only, no sulfur in 1971. 6 ALABAMA AGRICULTURAL EXPERIMENT STATION times between 140 and 160 days after planting; optimal harvest date is reported. here. Leafspot incidence (Cercospora + Cercosporidium) was determined 14 days before harvest by removing 10 non-bearing vertical runners at random from each plot and measuring infection using the following criteria: (i) total leaflets = number of leaf nodes x 4; (ii) percent defoliated = number of leaflets lost - total leaflets x 100; (iii) total leaflets infected = number of leaflets lost + number of leaflets infected; and (iv) percent infection = leaflets infected - total leaflets x 100. This method assumes that defoliation occurred because of previous leafspot infection. Summary data for fungicides, presented in tables 1-3, indicate that all performed adequately in controlling leafspot. However, there were significant differences in the means. The high figure for disease in Benlate-treated plots in 1974 reflects the occurrence of a Benlate-resistant race of Cercospora that caused severe infecTABLE 2. PERCENT DEFOLIATION OF FLORUNNER PEANUTS BY CerCOSpora AND Cercosporidium FOLLOWING TREATMENT WITH FOLIAR FUNGICIDES Percent defoliation Treatment 1971 1972 53.0 6.4 5.3 18.5 12.1 a d d b c 1973 44.0 5.8 6.1 12.4 2.6 a bc bc b c 1974 Mean" Control ....---------............ a ___79.9 Bravo 6F _____________43.4 c ................ Benlate 50WP 24.8 d 50.2 bc Duter 47WP -........ Kocide 404S F3 ...... 56.3 b ------- 64.4 a 15.0 c 55.12b 33.1 c 18.7 c 59.3 22.7 17.5 30.3 20.7 a c d b cd Values within columns followed by the same letter are not significantly different at the 5 percent level using Duncan's Multiple Range Test. 1 Mean weighted for number of replications in each year's test. 2 Resistance to Benlate developed in Cercospora during the 1973-74 seasons. 3 Cu[O'H]2 only, no sulfur in 1971. TABLE 3. YIELDS OBTAINED FROM PEANUT LEAFSPOT CONTROL TESTS, 1971-74 Treatment Pounds per acre 1971 3,589 3,792 3,136 3,1763 1972 3,176 1973 2,389 1974 2,817 Mean' 2,558 d Control ... ....... 1,851 Bravo 6F ...... Benlate 50WP... Duter 47WP .... Kocide 404S F... 3,283 3,594 3,533 3,390 3,531 2,926 2,743 3,277 4,653 2,8342 4,319 4,523 3,889 3,286 3,433 3,591 a c bc b Values within columns followed by the same letter are not significantly different at the 5 percent level using Duncan's Multiple Range Test. 1 Mean weighted for number of replications in each year's test. 2 Resistance to Benlate developed in Cercospora during the 1973-74 seasons. 3 Cu[OH] 2 only, no sulfur in 1971. TABLE 4. RESULTS OF FUNGICIDE TRIALS FOR PEANUT LEAFSPOT CONTROL, 1975-76 Fungicide, rate' per acre Infection 1975 Pct. 1 Nontreated control 3 4 5 6 m Yield (147 days) 1975 Lb. 2,403 3,035 3,557 3,035 Defoliation Av. Pct. 75.8 Yield (137 days) 1975 Lb. 2,984 3,056 3,427 3,389 3,615 3,601 z c 1976 Pct. 72.4 1975 Pct. 58.9 50.0 39.7 43.9 37.8 43.3 25.2 40.0 40.8 26.5 37.6 39.4 41.7 1976 Pct. 48.4 43.7 35.1 33.6 26.3 29.3 16.8 32.5 30.3 24.1 25.0 27.3 - Av. Pct. 53.6 46.8 37.4 38.7 32.0 36.3 21.0 36.2 35.5 25.3 31.3 33.3 - 1976 Lb. 3,521 3,325 3,688 3,877 3,674 Av. Lb. 3,253 3,190 3,557 3,633 3,644 3,666 1976 Lb. 2,192 2,265 2,817 Av. Lb. 2,298 2,650 3,187 3,056 -------------79.2 2 Benlate, 6 oz. ---------------------------------- 7 9 10 11 12 13 14 73.8 Benlate-Manzate-Oil, 4 oz.-1.5 lb. + 1 qt. 65.9 Dithane + Oil, 2 lb. + 1 qt. 67.8 Kocide 404-S, 2 qt. ----67.1 Super-6 (S-6), 2 qt. ---68.7 Difolatan, 3 pt. -------51.7 --------- 68.8 55.0 55.3 46.0 52.6 56.8 45.8 36.0 41.5 71.3 60.4 61.5 56.5 60.6 60.9 53.7 44.7 53.4 0 -i 3,078 3,732 3,514 4.022 3,877 3,237 3,761 3,804 - 33.0-42.3 8 Duter. 6 oz. - --------------- 65.1 Bay Meb, 8 oz.-------------------61.6 SN-513 30% L, 3 pt. -------53.4 Bravo, 1.5 pt. ---------- --- --- ---65.4 Duter + T-H Sulfur, 6 oz. + 1 qt. ----- 61.2 Manzate-Oil, 1.5 lb. + 1 qt. ------------ 69.3 Manzate 200, 1.5 lb. --------------------65.7 15 Benlate + Manzate 200, 6 oz. + 2 lb. 68.4 16 DPX-112 + Oil, 2 lb. + 1 qt. ---------- 69.4 17 DPX-112, 2 lb. 48.6 - 54.9 - --72.2 64.4 - 65.1 - 46.1 43.8 42.1 45.9 42.9 38.9 39.0 23.6 31.8 41.7 - 43.9 - - - ---------------------- 18 19 20 21 22 Dithane + Super-6, Kocide 101-S, 2 lb. Fungisperse, 2 gal. Difolatan, 6 pt. (2) Difolatan, 2 pt. (3) 1.5 lb. ± 2 qt.------ 73.2 --------------------67.3 --------------------66.8 3 Pt. (5) ------------ 49.0 3 pt. (4) ------58.1 - - 4,095 3.671 4,028 3,812 3,981 3,639 3,578 3,464 3.331 3,052 3,395 3,589 3,572 3,499 4,074 4,056 3,804 3.846 3,952 3,524 3,871 3,721 - 2,976 3,296 4,037 3.572 3,717 3,804 3,862 3,528 2,933 3,078 3,165 3,078 3,107 3.209 2,962 2,541 3,499 2,875 - 3,070 3,187 3,572 3,390 3,339 3,172 3,680 3,201 2,817 - z r- 3,876 - 3,670 - 2,555 - 3,310 3,412 2,904 3,238 2,802 3,600 4,080 3,877 Continued TABLE 4 (CONTINUED). RESULTS OF FUNGICIDE TRIALS FOR LEAFSPOT CONTROL, 1975-76 Infection Fungicide, rate' per acre Pct. 23 24 25 26 27 28 29 30 31 32 33 Duter + Kocide, 3 oz. + 1 qt. Kocide 404 + Super-6, 2 qt. + 2 qt. Bravo + Super-6, 1.5 pt. + 2 qt. SN-513 30% L, 6 Pt.Oxycop LS, 3 qt.---Benlate + Oil, 6 oz. 1 qt. Bravo, 1.5 pt. (5) Bravo, 1.0 pt.-- - - - - - - - - - Bravo-Manzate, 1.5 Pt. (4) 1.5 lb. (3) Bravo/Duter (alternate), 1.5 pt./6 oz. Difolatan, 3 Pt. (5) 71.6 60.1 Defoliation Av. 1975 19761 Pct. 1975 Pct. 1976 Pct. - Av. Pct. - Yield (137 days) 1975 1976 Av. Lb. 3,488 3,726 3,874 3,842 3,891 3,389 Lb. Lb. Yield (147 days) 1975 1976 Av. Lb. 3,325 3,717 3,674 3,949 3,600 3,049 Lb. - P ct. - Lb. - 4- 58.9 49.2 60.2 71.5 46.1 30.3 35.1 25.0 36.9 45.8 - - -- -- 2,628 3,659 53.8 29.4 -3,107 3,485 36.4 58.6 2,788 3,688 38.8 58.4 -3,020 3,819 56.2 33.6 3,006 35.4 3,732 18.3 3,049 34 Difolatan, 3 Pt. (3) ; 2 pt. (4) ----------_ 3,630 18.5 36.4 3,034 35 Dithane M -45, 3 lb. -------------------58.8 37.5 3,949 36 R-H 5532, 1.5 lb. - 2,759 -----------------------3,630 67.2 42.0 3,470 37 EL-222, 40Ogai -----------------------4,385 48.4 30.2 2,802 38 EL-222, 60 g ai 3,978 ----------------------31.4 41.1 39 EL-228, 40 gai 3,165 ----------------------3,920 46.7 27.4 40 EL -228, 60 g ai ---------------- -------3,543 4,501 34.6 26.3 41 DPX -110, 3 lb.---------------2,817 3,819 ---- ----50.7 39.4 3,093 42 4.5 lb. -----------3,804 ----54.5 34.5 43 Benlate + Duter (mix) , 4 oz. + 5 oz. 3,180 49.1 3,906 32.1 urrvru~ull) u r~ \y/ ________________________________________ -JJ~L ~V~ 1 Brackets ( ) indicate number of sprays at a particular rate. All treatments received seven applications except treatments 29 and 0 C C 7- m x IV m DPX-1l0, z -4 33 which received only the first five applications. z PEANUT LEAFSPOT RESEARCH IN ALABAMA 9 tion and defoliation. Data on the newly recommended fungicides Difolatan 4F (3 pints per acre) and Duter plus sulfur (6 ounces + 11/ pounds per acre) are given in Table 4. This table, which lists all fungicides tested during 1975 and 1976, indicates the number of fungicides tested and discarded each year. Table 3 gives annual and multi-year yield averages for peanuts sprayed with the major fungicides. These figures reveal important differences in yield and generally show that although yield is usually an indicator of disease control, for some fungicides yields lower than expected are obtained. These deviations from expected yields will be covered in depth in the following sections. Appendix 3 lists the 1977 recommended fungicides for peanut leafspot control based on these and other data and gives suggested operational procedures for best results. Tolerance of Leafspot Fungi to Benlate Two fungi, Cercospora arachidicola and Cercosporidium personatum, cause leafspot of peanuts; both were controlled effectively with Benlate 50WP until 1973. Tolerance to Benlate has been reported in Cercospora apii Fries (3,4) and C. beticola Sacc. (13). In 1973, inadequate leafspot control was observed in several fields in southern Alabama which were being sprayed with the recommended Benlate program of 6 ounces per acre applied at 14-day intervals. Tests were conducted to determine: (1) if C. arachidicola and C. personatum had developed tolerance to benomyl (the active ingredient in Benlate), (2) if the proportion of Benlate-tolerant biotypes of Cercospora in problem areas differed from that in other areas, and (3) if the tolerance detected also applied to fungicide chemicals related to Benlate. Leaves infected with Cercospora and Cercosporidium spp. were obtained from fields with three different leafspot control histories. Field 1 was an isolated peanut field in an area where peanuts were not grown and which had never received Benlate; field 2 received Benlate and other fungicides in previous years and Benlate exclusively in 1973 with good results; field 3 received Benlate in 1973 but not in 1971-72 (area surrounding field 3 had extensive use of Benlate in 1971 and 1972), with adequate control. Leaves from each field were washed, placed on moistened filter paper in petri dishes, and incubated at 28 0 C for 4-6 days under constant illumination by white fluorescent tubes. Sporulating lesions were either sampled immediately or were air-dried for subsequent use. Single 10 ALABAMA AGRICULTURAL EXPERIMENT STATION spores removed from the lesions were placed on PDA-tetracyclinestreptomycin agar (PDATS) and subsequently examined at weekly intervals for 6 weeks (18). Mycelial fragments from colonies which developed on the original fungicide-amended media were transferred to media containing different fungicides and rated to observe the effect on colony growth. Fungicides and rates tested were Benlate at 5 and 50 p.p.m., thiophanate methyl (Topsin M 70WP) at 5 and 50 p.p.m., and Chemagro's Bay Dam 18654 at 5 p.p.m. All fungicides for these tests and also for the spore germination tests were added to the PDATS after autoclaving. Spores of C. arachidicola and C. personatum germinated on PDATS plates containing 5 p.p.m. benomyl. However, marked differences in development after germination were noted. Some germ tubes ceased development early and were assumed to be susceptible, while others showed tolerance by continuing to grow and producing viable colonies in the presence of the fungicide. An intermediate response was also noted, in which the spores germinated and showed some growth, but failed to develop into viable colonies. Growth on PDATS amended with 5 p.p.m. benomyl was considered indicative of tolerance, since 0.5 p.p.m. was adequate to inhibit development of C. arachidicolawhen Benlate first became available (unpublished data from the authors). Other investigators (3) showed earlier that, prior to the development of tolerance to Benlate by C. apii, less than 1.0 p.p.m. of benomyl was sufficient to completely inhibit growth of that species. Spores of C. arachidicola from field 1 showed little tolerance, Table 5, since only 1.0 percent of the spores exhibited short-term growth. TABLE 5. GERMINATION AND GROWTH OF Cercospora arachidicolaSPORES ON CONTROL AND BENOMYL-AMENDED MEDIA Fieldi Medium 2 Total No. 40 105 112 spores Germi- nation Pct. 78 89 95 Short-term growth Pct. 0 1 0 Continued growth3 Pct. 100 0 100 1 2 PDA PDA + PDA 5 p.p.m. 3 PDA + 5 p.p.m. PDA PDA + 5 p.p.m. 107 28 41 96 79 78 82 0 56 1 100 44 1 Field 1, no present or past leafspot control with Benlate; field 2, good leafspot control with Benlate in 1973; and field 3, poor leafspot control with Benlate in 1973. 2 Concentration expressed as p.p.m. of active ingredient of formulated product: Benomyl 50% W.P. 3 Calculated on basis of spores that germinated. PEANUT LEAFSPOT- RESEARCH IN ALABAMA 11 An intermediate level of tolerance probably existed in field 2, where 82 percent of the isolated spores showed short-term growth and 1.0 percent produced viable cultures on the PDATS amended with 5 p.p.m. benomyl. Forty-four percent of the spores from field 3 developed and formed typical colonies on the fungicideamended medium, indicating a level of tolerance sufficiently high to cause inadequate control by Benlate of leafspot in the field. Cercosporidium personatum occurred at a low frequency in the three test fields; however, development of germ tubes from spores plated on fungicide-amended medium was similar to that obtained with C. arachidicola. Cultures tolerant to 5 p.p.m. benomyl were obtained. Transfer of cultures of C. arachidicola resistant to 5 p.p.m. benomyl indicated that these cultures could tolerate 50 p.p.m. benomyl, 50 p.p.m. thiophanate methyl (Topsin-M), and 5 p.p.m. Bay Dam 18654. Growth at 50 p.p.m. benomyl and thiophanate methyl was much slower than at the lower concentrations. Since Benlate and Topsin-M have a common fungitoxic breakdown product, MBC (methyl 2-benzimidizolecarbamate) (5,8), it is probable that the tolerance observed in these biotypes was to MBC. Because of the data obtained in this study, Benlate was removed from the list of recommended fungicides for the 1974 season. A conservative estimate made in 1974 indicated that at least 30 percent of Alabama's peanut acreage was infested with Cercospora strains resistant to Benlate. If growers farming these acres had not followed Auburn's new recommendations, losses of 40 percent would have resulted. Thus, a potential loss of $7 million to Alabama peanut production was averted, and a new average yield record was established. Effects on Kernel Quality and Crop Value Throughout the studies on leafspot control, samples of harvested pods were obtained and graded according to standards set by the Federal-State Inspection Service (20). Value per harvested ton and value per acre (yield x value) were computed. Multi-year analyses of kernel quality, Table 6, indicated a significant (p < 0.05) decrease in value per ton for peanuts from fungicide treated plots in comparison with control plots. Grade data indicated that the inferior quality was due to damage to the mature kernels and that this damage was caused by fungi. Kernels 12 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 6. KERNEL QUALITY VALUES OBTAINED FROM PEANUT LEAFSPOT CONTROL TESTS, 1971-74 Treatment 1971 1972 Value per ton 1973 1974 Mean' $ Control Bravo 6F 304.46 301.04 $ 296.38 290.57 $ 298.25 276.89 $ 408.95 397.98 327.03 a 316.56 b Benlate 50WP .......... 296.97 Duter 47WP ............ 298.53 Kocide 404S F --------- 300.792 281.32 284.45 298.91 268.23 239.39 291.29 395.21 367.41 385.92 310.64 b 298.33 c 312.94 b Values within columns followed by the same letter are not significant at the 5 percent level of probability using Duncan's Multiple Range Test. 1 Mean weighted for number of replications in each year's test. 2 Cu[OH]2 only, no sulfur in 1971. from the control plots were significantly better in quality than the fungicide plots. Kernel quality of peanuts from plots treated with Bravo was slightly better than that from other fungicide treatments, but was inferior to the quality of kernels from control plots. Peanuts from plots treated with Duter were significantly (p < 0.05) lower in quality than any of the other fungicide treatments or the control. In comparisons of yield, quality, and value per acre, Bravo returned more money than any other fungicide tested or the control, Table 7. The level of disease control achieved with all test fungicides was significantly better than the untreated control, tables 1 and 2, yet kernel quality of peanuts from all fungicide-treated plots was inferior to that of the non-treated control plots, Table 6. Data from this study, and from one covered in the following section, indicated that maintenance of a complete foliar canopy alters the subcanopy environment with a resulting deterioration of kernel quality (2). These data also indicate another possible mechanism TABLE 7. YIELD, QUALITY, AND VALUE PER ACRE OBTAINED FROM PEANUT LEAFSPOT CONTROL TrESTS, 1971-74 Treatment Yield/acre d a c bc b Value/ton $ 327.03 316.56 310.64 298.33 312.94 a b b c b Value/acre $ 418.27 615.55 510.38 512.08 561.88 d a c be Lb. 2,558 .........-------------Control 3,889 Bravo 6F .......-------------........ .......---.. 3,286 Benlate 50WP------. .. ...--3,433 Duter 47WP Kocide 404S F ........--------- 3,591 b Values within columns followed by the same letter are not significantly different at the 5 percent level of probability using Duncan's New Multiple Range Test. PEANUT LEAFSPOT RESEARCH IN ALABAMA 13 for kernel quality effects: direct toxic effects of the foliar fungicides on soil-borne pathogens or their natural antagonists may occur. Thus, kernels of superior quality would be expected from plots where the fungicide exhibited toxicity to the pathogen(s), but where little or no effect on the antagonist(s) occurred. Inferior-quality kernels would occur in plots where fungicides exhibited toxicity to the antagonist(s), but with little or no effect on the quality-deteriorating pathogens. Several observations support this hypothesis. First, similar levels of defoliation were obtained when Benlate, Duter, or Kocide were used to control leafspot. However, use of Duter resulted in significantly inferior kernels when compared to the other two fungicides. Secondly, when values for kernel quality were examined, peanuts from the control plot had a significantly higher dollar value per ton than those from any of the fungicide treatments. If a true inverse relationship exists between leaf maintenance and kernel quality, then Benlate or Kocide-treated plots (which had the least defoliation) should have had the poorest kernel quality of any fungicidetreated plots; however, they were not significantly lower in quality than those from the Bravo-treated plots. A third indication that toxic action by the fungicides altered the ecology of the geocarposphere (soil immediately surrounding the pod) was observed with Benlate. Benlate was extremely effective as a leafspot control fungicide in 1971 and 1972. However, during 1973 Cercospora developed resistance to this fungicide (7), and in 1974 defoliation in Benlate-treated plots was nearly equal to that of the control. Data for Benlate-treated plots over the 4-year period showed no improvement in kernel quality as defoliation levels increased. While not conclusive, these observations indicate that the toxic effects of fungicides on natural antagonists or pathogens are more important to kernel quality than the degree of leaf maintenance and the resulting canopy. Additional research is necessary to determine: (1) the extent to which each mechanism affects kernel quality, and (2) whether any interactions exist (14). Fungicide Effects on White Mold (Sclerotium rolfsii) After 1970 peanut farmers in the Southeast became increasingly aware of losses to white mold (southern stem blight) caused by Sclerotium rolfsii. Effective leafspot control procedures adopted during this period made -at least three major changes to the ecol- 14 ALABAMA AGRICULTURAL EXPERIMENT STATION ogy of soil-borne fungi: (1) few leaves were lost to the soil surface to serve as organic food sources for the white mold fungus; (2) fungicides were prevented from reaching the soil by the "umbrella effect" of the intact canopy; and (3) an altered sub-canopy environment was created which may be stimulatory to soil-borne fungi. Previous workers (10,11) indicated that S. rolfsii is more severe when defoliation provides an organic food base. Those studies were made when effective fungicides for leafspot control were not available, and were of necessity performed under high levels of defoliation. Increased levels of S. rolfsii damage in fields with excellent leafspot control indicated that something other than a food base of leaf litter was involved in white mold severity. A study was made during the 1972 and 1973 seasons to determine: (1) the significance of defoliation on severity of white mold; (2) the importance of canopy in shielding the soil from foliar fungicides and the contribution of sub-canopy environment to disease severity; and (3) the relationship between the incidence of S. rolfsii and the toxicity of leafspot fungicides to this pathogen and the natural antagonist Trichoderma viride (Pers. ex. Fr.). Spraying operations and leafspot evaluations were conducted as described previously. White mold damage was determined by counting the number of dead areas showing signs of the fungus in the center two rows of each plot (17). Two tests were conducted in 1973. In a laboratory test, Benlate, Bravo, and Topsin M were incorporated into potato dextrose agar (PDA, Difco) at concentrations of 0.5 and 5.0 p.p.m., and Kocide was used at 50 and 250 p.p.m. (based on Cu[OH] 2 ). Twenty ml of each medium and a no-fungicide control were poured into 90-mm diameter petri dishes. Each TABLE 8. OCCURRENCE OF WHITE MOLD (S. rolfsii) IN PEANUT FIELD PLOTS FOLLOWING APPLICATION OF LEAFSPOT FUNGICIDES Dead sites/100 ft. row Treatment 1972 1973A 1.88 6.12 3.88 2.00 5.12 3.23 3.47 1973B 1.80 Meant 1.92 4.94 3.49 2.45 3.29 1.46 1.94 Untreated control......... 2.17 3.75 Benlate 50WP ............ Bravo 6F .....................2.83 3.17 Kocide 404S F 1.50 Topsin 70WP LSD (P = LSD (P = 0.05) 0.01) 2.68 3.76 4.00 3.40 2.60 1.80 2.10 2.90 1 Mean weighted for number of replications in each experiment. PEANUT LEAFSPOT RESEARCH IN ALABAMA 15 treatment was replicated 10 times, five of which were inoculated with one disc (7 mm diameter) of T. viride and five with S. rolfsii. Inoculum discs were removed from the periphery of 48-hour-old cultures growing on PDA. Radial growth of each fungus was measured 36 hours after inoculation. Field tests revealed only minor differences in peanut leafspot control among fungicide treatments, tables 1 and 2. However, multi-year analysis indicated that these small differences in leafspot control reflected disproportionate differences in peanut yield and quality, tables 3 and 6. Numbers of plants killed by S. rolfsii were significantly different (P = 0.01) among treatments, Table 8. Laboratory studies showed that the various foliar fungicides differed greatly in effects on S. rolfsii and its antagonist T. viride, Table 9. In agar medium, Benlate was the only fungicide displaying little or no effect on the pathogen but toxicity to the antagonist. The fungi showed intermediate responses to the other fungicides. TABLE 9. COMPARISON OF DISEASE OCCURRENCE IN PEANUT FIELD PLOTS WITH GROWTH OF Sclerotium rolfsii AND Trichoderma viride ON FUNGICIDE-AMENDED POTATO DEXTROSE AGAR (PDA) Fungicide Rate No. dead Radial growthl (mm) treatment p.p.m. sites S. rolfsii Trichoderma PDA control Benlate Benlate Bravo Bravo -0.5 5.0 0.5 5.0 1.92 4.94 3.49 - 15.3 16.2 14.8 9.0 4.0 20.5 4.5 0 12.0 4.8 Kocide 404S F 50.0 Kocide 404S F ......... 250.0 Topsin M 0.5 Topsin M -............ _ 5.0 2.45 3.29 - 15.8 13.0 16.2 16.8 11.8 3.8 20.0 5.5 1 Radial growth in mm (longest axis -}- shortest axis) - 2 on PDA culture plate; average of five replications. The importance of leaf retention in increasing white mold damage can be determined by comparing the untreated control plot to those receiving fungicide treatments. In all cases the control, with a high level of leafspot infection (and defoliation), had the least white mold damage. This observation was confirmed by comparing Benlate-treated plots to Benlate-treated plots that had been clipped (mechanically defoliated) or hormone-treated (plant size reduced without defoliation). Clipped plots treated with Benlate had significantly less (P = 0.01) white mold damage than 16 ALABAMA AGRICULTURAL EXPERIMENT STATION non-clipped plots treated with Benlate, Table 10. Clipping fungicide-treated plots reduced white mold damage to a level similar to the unsprayed control plots. All experiments reported in this section were conducted during dry growing conditions (30 days or more of drought after blooming). In the authors' opinion, under dry conditions an intact canopy creates and maintains a humid atmosphere that is conducive to fungal growth and disease development; the more defoliated control plots would be subject to greater fluctuations in soil moisture, since they would not have sufficient leaves to maintain a humid atmosphere. This would be obviated in peanuts grown under irrigation or during wet seasons. Differences in levels of damage from white mold among fungicide plots can be related to fungicide effects on the pathogen and,! or its natural antagonist Trichoderma spp, Table 9. Benlatetreated plots had the highest incidence of white mold. Benlate exhibited no in vitro effect on S. rolfsii, while exhibiting a toxic effect on Trichoderma. The related benzimidazole, Topsin-M, was equally innocuous to S. rolfsii but displayed only mild toxicity to Trichoderma. The significant difference (P = 0.05) in field levels of white mold between these two treatments indicates a probable role for Trichoderma in reducing S. rolfsii damage under natural conditions. Fungicides having a direct toxic effect to S. rolfsii in the laboratory (e.g. Bravo) did not show the field reduction of incidence in S. rolfsii that might have been inferred from laboratory data. Bravo should have had the lowest damage because it was the most toxic fungicide to S. rolfsii and least toxic to Trichoderma. The fact that it did not perform as expected may indicate the importance of a complete canopy as well as point to other soil ecological factors that may play a role in S. rolfsii severity. In addition, data not presented here indicate that Bravo is an excellent contact fungicide but is inactive once it contacts the soil. TABLE 10. THE EFFECT OF FOLIAGE CLIPPING AND A GROWTH REGULATING HORMONE ON WHITE MOLD AND YIELD IN PEANUT FIELD PLOTS Treatment Dead sites/ 100 ft. of row No. 7.2 Yield/acre Lb. 2,266 Benlate ---------------------- ------- -- Benlate + hormone-------------------Benlate (clipped) LSD (P = LSD (P = 0.05) 0.01) 5.7 3.8 3.23 3.47 2,003 2,175 NS NS PEANUT LEAFSPOT RESEARCH IN ALABAMA 17 These data indicate that researchers should be aware of and observe non-target effects of leafspot fungicides. Both yield and crop quality can be severely affected. The farmer, on the other hand, should be aware that control of peanut leafspot may lead to changes in the severity of other diseases. For white mold, the old theory of leaf defoliation causing increased severity has been disproved; good leafspot control will cause greater white mold damage. The following section will relate leaf loss and white mold damage to yield. The Relationship between Leaf Loss and Yield For the past 4 years Auburn research has sought to define the relationship between leaf loss and yield. Statistical evaluation of more than a thousand research plots revealed that a farmer with a projected yield of 3,000 pounds per acre using recommended leafspot fungicides will lose 14 pounds per acre for every 1 percent increase in leafspot. The best fungicides usually reduce infection to 10-15 percent, while poorer products allow 40-60 percent infection. This means at least 400 additional pounds are lost if 40 percent of the leaves have spots or have fallen off just because a poor fungicide was chosen instead of an effective one, or the spray interval was too long. Even the best fungicides presently recommended still allow yield reductions of 150 pounds per acre due to leafspot. When rates of leafspot infection higher than 40 percent occur, leaf loss is even more important, resulting in yield reductions greater than 14 pounds per percent. In 1974 a 1,300-pound difference in yield occurred between plots with 25 percent infection and those with 90 percent infection. These data emphasize the advantages of adequate leafspot control. In addition, they serve to illustrate why peanut farmers should continue their leafspot programs despite increased white mold losses. Farmers should, however, use recommended soil fungicides on land where white mold has been severe. Fungicide Effects on Foliar-feeding Insects 4 Observations of soybeans treated with fungicides indicate that some fungicides reduce insect damage to leaves, while others ac4 In cooperation with Dr. James D. Harper, Department of Zoology-Entomology. i8 ALABAMA AGRICULTURAL EXPERIMENT STATION tually increase insect damage. A field test was conducted in 1975 to determine if insect populations were affected by leafspot fungicides. Plots of peanuts were sprayed with fungicides and evaluated for incidence of leafspot, stem rot, and insect feeding damage. Standard recommended fungicides and rates, applied on a 14-day schedule, were: Difolatan 4F, 3 pints per acre; Kocide 404-S, 2 quarts per acre; Bravo 6F, 1.5 pints per acre; and Duter 47WP, 6 ounces per acre. GTA (guazatine triacetate, SN-513) 30% L was compared on the same schedule to these fungicides and a nontreated control at rates of 3 and 6 pints per acre. Plots were 24 x 50 feet with eight rows per plot. Treatments were replicated six times. All fungicides were applied with a conventional ground sprayer delivering 14 gallons per acre at an operating pressure of 60 p.s.i. Leafspot incidence (Cercospora + Cercosporidium) was evaluated 14 days before harvest using criteria discussed previously. Stem rot was determined 10 days before harvest by counting the number of disease loci in the two center rows of each plot showing signs of white mold infection (17). Insect defoliation was evaluated the day before harvest by visual estimate using a linear scale of 1-5 (1 = no evidence of insect feeding, 5 = totally defoliated). After digging and air-drying, peanuts were harvested with a Lilliston 1500 combine with sacking attachment. Only the two center rows of each plot were harvested. Soybean looper, Pseudoplusia includens Walker, and soybean, Glycine max L., were chosen as a model host-insect system for laboratory tests to verify field observations of repellency and antifeeding effects. Fully expanded soybean leaves (trifoliates) were excised from greenhouse-grown plants, placed on a laboratory belt sprayer, and treated with GTA at rates of 0, 1.5, 3.0, and 6.0 pints per acre. All treatments were applied using a carrier volume of 30 gallons per acre and a pressure of 60 p.s.i. Sprayed leaves were maintained by wrapping the petiole in cotton which was then used to stopper water-filled shell vials. Two vials with leaves were placed in each petri dish. Three 5th-instar soybean looper larvae were then placed in each dish, and leaf area consumed was recorded after 24 and 48 hours. All rates were replicated four times. In a similar study, the 0 and 1.5 pints per acre rates of GTA were compared in a feeding preference test. Two vials, one containing a treated leaf and the other containing an untreated leaf, PEANUT LEAFSPOT RESEARCH IN ALABAMA 19 were placed in each of five dishes. Three soybean looper larvae were added to each dish and percentage leaf area consumed was determined for each leaf. Contact toxicity of GTA at rates from 1.5 to 6.0 pints per acre was rated by spraying 5th-instar soybean looper larvae directly on the belt sprayer. Insects were placed on rearing medium and observed at intervals until pupation. Repellency of GTA to soybean looper moths was tested by releasing 10 moths in a cage containing one peanut plant for each of the following fungicides and rates per acre: (1) non-sprayed control; (2) GTA, 1.5 pints; (3) GTA, 3.0 pints; and (4) Cyprex (a fungicide related to GTA), 1.5 pounds. Treatments were replicated in a randomized complete block design. Plants were maintained in a greenhouse at 82 ± 50 F with 16 hours of daylight. Egg deposition was observed 2 days after moth release and feeding damage by hatched larvae was assessed at 7 and 12 days after release. Oral toxicity of GTA to 5th-instar soybean looper larvae was also determined. GTA solutions ranging in concentration from 0.0001-0.24 mg per l were delivered in volumes of 4 or 8 l into the foreguts of 10 larvae by means of a microsyringe (16). Larval mortality was recorded 24 hours after forced feeding. Control of peanut leafspot with 3.0 and 6.0 pints per acre of GTA equalled that with recommended fungicides, Table 11. GTA demonstrated a slight burn of peanut foliage when leaves were inspected for leafspot control. Phytotoxicity was evidenced by brown to dark brown spotting of the leaf; its effect on yield TABLE 11. EFFECT OF PEANUT LEAFSPOT FUNGICIDES ON TARGET PESTS, NON-TARGET PESTS, AND CROP YIELD, 1975 Leafspot control Infection Defoliation Insect 1 damage Stem rot sites/30 m Pct. -_--- 79.3 Control GTA 30% L, 3.0 pints...... 53.4 GTA 30% L, 6.0 pints ...... 49.2 Duter 47 WP, 6.0 ounces... 61.2 51.7 Difolatan, 3 pints Bravo 6F, 1.5 pints ........ 63.4 Kocide 404S, 2 quarts .........67.1 Pct. 61.2 26.5 25.0 39.4 25.2 37.6 37.8 2.8 1.8 1.4 3.4 3.3 3.4 3.5 No. 3.0 5.2 4.8 3.6 4.8 5.2 5.8 Lb. 2,985 3,811 3,847 3,638 4,094 3,981 3,653 1 Insect damage rated on a 1-5 scale, where 1 = no damage, 2 -= 25 percent, 3 50 percent, 4 = 75 percent, and 5 = 100 percent of leaf area lost. Control insect damage is artificially low due to severe defoliation from leafspot infections. 20 ALABAMA AGRICULTURAL EXPERIMENT STATION could not be determined. GTA showed no improvement in stem rot control over the recommended leafspot fungicides. However, GTA-treated plots showed reductions in defoliation by lepidopterous larvae, Table 11. Insects found in the peanut plots included the corn earworm, Heliothis zea (Boddie), velvetbean caterpillar, Anticarsia gemmatalis Hibner, and beet armyworm, Spodoptera exigua (Htibner). Visual estimates of damage showed GTA-treated plots to have only 10-20 percent average defoliation. Most of this damage occurred on new, untreated foliage. Peanut leaves treated with all other fungicides sustained 60-65 percent average defoliation. The untreated control plots had an intermediate insect damage rating (about 40 percent) because many of the insect damaged leaves abscissed prior to rating of leaves for leafspot damage. In greenhouse and laboratory studies, GTA was a repellent to soybean looper larvae, Table 12. When treated leaves were the only food available, they were never completely consumed, even after 48 hours; consumption decreased with increasing dosage, Table 12. Larvae feeding on untreated foliage consumed all available leaves within the first 24 hours. When larvae were given the choice of an untreated leaf and a treated leaf, Table 12, the untreated leaf was always consumed within 24 hours while the treated leaf was not completely consumed even after 48 hours. Direct spraying of larvae at 6.0 pints per acre had no apparent deleterious effect since all sprayed larvae progressed normally to pupation. Larvae that were force-fed GTA solutions tolerated all dosages < 0.24 mg per larvae, Figure 1. Dosages of > 0.71 mg per larvae caused 100 percent mortality within 24 hours. TABLE 12. PERCENT OF SOYBEAN LEAF AREAS CONSUMED BY SOYBEAN AFTER TREATMENT WITH GUAZATINE TRIACETATE1 LOOPER LARVAE Test Rate, pints/acre 0 1.5 52 88 3.0 10 23 6.0 8 18 Repellency 24 hours -100 48 hours -- 2 Preference3 8 24 hours -100 48 hours -2 88 1 All values presented are averages from 4 replicates. 2 Food supply was exhausted in first 24-hour feeding period; further consumption was impossible. 3Untreated and treated leaves simultaneously available. PEANUT LEAFSPOT RESEARCH IN ALABAMA 21 In oviposition tests, moths deposited most of their eggs on cage walls. Those few which were placed on plants were uniformly distributed over all treatments. However, where significant levels of egg-laying occurred on treated peanuts, larvae continued to feed only on check plants or on those treated with Cyprex. On GTA-treated peanuts, feeding was initiated but ceased before significant leaf damage had occurred. These data indicate that GTA is an effective fungicide for peanut leafspot control when applied at rates of 3 pints per acre or greater. Further, this fungicide significantly reduced feeding damage by lepidopterous larvae (12). No evidence of an antifeeding effect could be found for any other fungicide in the field test. The laboratory tests with P. includens indicated that GTA had an anti-feeding effect based primarily on repellency. Larvae showed a feeding preference for untreated foliage over treated foliage. Observations further indicated that, at least for small larvae, feeding occurred on the surface of the leaf opposite the treated surface. Larvae that did ingest treated foliage showed no ill effects. Forced feeding demonstrated acute toxicity of GTA, but the amounts required to kill larvae are several times higher than individual larvae would normally consume on treated foliage. A spray mix applied uniformly over 1 acre of leaf surface at the rate of 3.0 pints per acre would deposit a maximum 0.008 mg AI per cm 2 , assuming total deposit. Fifth-instar soybean looper larvae consume about 10 cm 2 of peanut leaves per 24 hours (J. D. Harper, unpublished data) and would, therefore, require more than 3 days of feeding to accumulate the minimum dose exhibiting toxicity. However, since the conditions described represent assumptions of maximal conditions, including a lack of repellency, it is highly unlikely that a lethal dosage would ever be ingested. GTA exhibits excellent fungicidal activity against peanut leafspot. In addition, these data indicate a true repellency of lepidopterous larvae. These features suggest that GTA is a likely candidate for inclusion in an integrated pest management system for peanuts. Its spectrum of repellency and use in other crops needs further investigation. EFFECT OF KYLAR ON PEANUT YIELDS The hormone Kylar (Succinic acid 2,2-dimethyl-hydrazide) has frequently been promoted for increased peanut yields. The re- 22 TABLE 13. ALABAMA AGRICULTURAL EXPERIMENT STATION EFFECT OF KYLAR ON DISEASE AND YIELD OF RUNNER PEANUT, 1973 Treatment Defoliation Pct. White mold dead sites No. Yield/ acre Lb. Value/ton $ Fungicides only -----Fungicides + Kylar at low rate ---- 10.0 .............11.4 3.78 2.84 4.19 1.18 2,497 2,327 2,232 145 300 291 292 N .S. Fungicides + Kylar at high rate -------------- 9.8 LSD .05 ---...- ......... . ................ N .S. ported reduction in vine growth was thought to reduce disease damage and equipment damage to vines. Experiments were conducted for 2 years at the Wiregrass Substation, Headland, to determine if these claims were accurate for Florunner peanuts grown in the Southeast. In 1973 Kylar was tested at two rates as a tank mix with various recommended fungicides. The low rate consisted of 1/ pound of Kylar 85W applied 55 days after planting with 1/4 pound applied four times at 14-day intervals thereafter. The high rate received 1/2 pound on all five dates. Treatments were replicated, eight times with each of four fungicides on 50-foot by four-row plots. Disease and yield were rated as previously described. A similar study was conducted in 1974, except that Kylar was applied three times at 1/2 pound with each of five fungicides and a control. Table 13 represents means of the Kylar + fungicide mixtures at each Kylar rate tested. These showed no effect on foliar disease, a slight reduction in white mold damage, and a slight yield reduction. Disease data from 1974 were similar to those presented in 1973, except yields were not depressed, Table 14. In conclusion, Kylar shows little benefit to overall yield in runTABLE 14. YIELDS OF SIX FUNGICIDE PROGRAMS WITH AND WITHOUT KYLAR PROGRAM, 1974 Yield, by fungicide treatment Hormone treatment No Benlatel Fungicide Lb. Lb. Bravo Lb. BenlateManzateoil Lb. Duter Lb. Dithane Lb. Mean Lb. No Kylar -........ 2,439 3,020 2,948 2,984 3,862 3,993 3,928 3,456 3,441 3,448 3,557 3,542 3,550 3,528 3,571 3,550 3,311 3,340 Kylar 1/2 lb. (3 times) -... Mean ------ 2,512 ..... 2,476 1 Benlate resistance. PEANUT LEAFSPOT RESEARCH IN ALABAMA 23 ner peanuts grown in Alabama, and therefore is not recommended by Auburn University. THE ROLE OF SULFUR IN LEAFSPOT CONTROL Sulfur was used extensively for peanut leafspot control until the mid-1960's when it was effectively replaced by organic fungicides. Studies have continued through the past several years to determine if the performance of these 'modern' fungicides can benefit from the addition of sulfur to the spray tank. Data in Table 15 illustrate results obtained with two formulations of Kocide during 1976. Differences between sulfurs in their ability to control peanut leafspot are apparent. Super-6 sulfur is produced by a wet-milling process and appeared to perform better than Stoller sulfur (molten sulfur process) or micronized sulfur (air-milled). These data were consistent over several years. Table 4 contains additional data (1976) in which Super-6 and Stoller sulfur (TH-S) were compared when added to Duter. These data are consistent with those developed when sulfur formulations were added to Kocide. The addition of sulfur to Duter (1973-76) is summarized in Table 16. On a multi-year basis there is a consistent improvement in disease control (reduced defoliation) and yield. These data inTABLE 15. EFFECT OF 3 COMMERCIAL SULFUR FORMULATIONS ON THE CONTROL OF PEANUT LEAFSPOT BY THE FUNGICIDE KOCIDE, 1976 Fungicide Kocide 404F Kocide 101 WP ............. M ean -------.... ...... With Super-6F Percent defoliation1 With With Stoller 6F micronized sulfur 10.4 17.5 14.0 -.... -- 10.2 12.2 .-11.2 13.7 - _ 1 Yields not reported due to severe drought. TABLE 16. EFFECT OF THE ADDITION OF SULFUR ON PEANUT LEAFSPOT CONTROL WITH DUTER Defoliation Fungicide 1973 Pct. 12.4 1974 Pct. 33.1 1975 Pct. 40.0 1976 Pct. 32.5 Av. Pct. 29.5 Yield, 1973-76 average Lb. 3,466 Duter .............. Duter + sulfur.. 6.8 24.4 39.4 26.1 24.2 3,629 24 ALABAMA AGRICULTURAL EXPERIMENT STATION dicate that sulfur definitely improves peanut leafspot disease control and yield for mid-range performing fungicides. Auburn recommendations for peanut leafspot control therefore suggest that sulfur be used with Kocide and Duter. Table 4 reflects the performance of Super-6 alone at 2 quarts per acre and Super-6 in combination with Bravo and Difolatan at recommended rates. Super-6 alone was effective as a fungicide, but when mixed with Bravo and Difolatan it did not improve disease control over that from Bravo and Difolatan used alone. As a nutritional aid sulfur would only help if a sulfur deficiency was present. Since Bravo and Difolatan showed neither an improvement in disease control nor an improvement in yield when sulfur was added, Table 4, it can be assumed that sulfur deficiency was not present in these tests. Tests conducted by the Department of Agronomy and Soils show that sulfur deficiencies are rare in Alabama peanuts (Dr. Fred Adams, personal communication). Sulfur should therefore be used only where a significant improvement in disease control can be expected (i.e. with Kocide and Duter). SPRAY EQUIPMENT AND DELIVERY RATES Methods of Application of Leafspot Fungicides Several types of spray equipment are used by peanut farmers, but no comprehensive comparisons of equipment performance have been made in the past. Beginning in 1970 an equipment comparison test was begun at the Wiregrass Substation. Each year four recommended fungicides were applied in replicated trials through each of three types of spray equipment: (1) a conventional ground sprayer that operated at 60 p.s.i. and 15-20 gallons per acre; (2) a low-volume ground sprayer (Span®) that delivered 4-5 gallons per acre using hydraulic fans for spray propulsion; and (3) an airplane equipped with a boom sprayer, that operated at 3-4 gallons per acre. Plot widths were adjusted for swath width (8 rows for conventional, 12 rows for low-volume, and 16 rows for the airplane). The middle six rows were used for disease samples and yield. Plot lengths were 150 feet and each treatment was replicated five times. Data are reported as the means of all fungicides applied by a given piece of equipment throughout the entire 3-year study, Table 17. PEANUT LEAFSPOT RESEARCH IN ALABAMA 25 TABLE 17. TYPE OF SPRAY EQUIPMENT AND ITS RELATIONSHIP TO PEANUT LEAFSPOT CONTROL WITH FUNGICIDES, 1970-72 Control measure Conventional ground sprayer Low-volume ground sprayer Low-volume airplane 45.1 24.8 3,609 581 Infection, pct. Defoliation, pct. Yield/acre, lb. Dead plantsl per acre (white mold) 36.3 19.9 3,706 356 36.7 19.2 3,742 487 1 1972 data only. These data revealed that conventional ground applications were generally equal to low-volume ground application for yield and disease control. Airplanes were slightly less effective, but as can be seen from Table 18 this was primarily due to the poor performance of Benlate when applied by air. Low-volume and airplane applications usually had higher white mold damage, probably a result of poorer fungicide penetration to the soil surface. Overall performance did not differ appreciably when the currently recommended contact fungicides were compared. The choice of equipment remains with the farmer. However, several areas of caution should be stressed: (1) never spray with lowvolume ground or airplane sprayers when windspeed is greater than 4-5 miles per hour; (2) adjust swath width to compensate for drift (fewer rows upwind, more rows downwind) for low-volume and airplane sprayers; and (3) accurately flag airplane swaths so that some overlap occurs to compensate for reduced spray deposition at the swath edge. The airplane is the sprayer of choice when prolonged wet weather prevents ground application. Severe disease can occur if application is delayed until the soil dries enough to support ground equipment. TABLE 18. DISEASE CONTROL AND YIELD IN PLOTS SPRAYED WITH BENLATE AND BRAVO (1970-1972) BY TYPES OF SPRAY EQUIPMENT Conventional ground Infec- Defolia- Yield/ acre tion tion Pct. Benlate-.. 21.4 Bravo-..... 35.2 Pct. 10.5 19.8 Lb. 3,882 3,908 Low-volume ground Infec- Defolia- Yield/ tion tion acre Pct. 22.6 39.3 Pct. 19.6 21.6 Lb. 3,813 3,889 Low-volume airplane Infec- Defolia- Yield/ tion tion acre Pct. 41.2 43.1 Pct. 22.6 21.1 Lb. 3,696 3,830 Fungicide 26 ALABAMA AGRICULTURAL EXPERIMENT STATION Delivery Rates for Ground Sprayers In 1971 a study was conducted to determine the optimal rate of water to use in delivery of peanut foliar fungicides by a conventional ground sprayer. The sprayer was adjusted to operate at 60 p.s.i., using three hollow-cone nozzles per row. Four fungicides were applied for each delivery rate. Fungicide x volume combinations were replicated four times each. Means reflect the average of all fungicides at each rate. Data indicate little difference between any of the delivery rates, Table 19, and suggest that farmers have a great deal of latitude with peanuts when choosing their delivery volume. Auburn currently recommends rates of 10-20 gallons per acre because there is more latitude for such factors as worn nozzles and nozzle height at the slightly higher rates. TABLE 19. WATER DELIVERY RATE PER ACRE AND ITS EFFECT ON THE PERFORMANCE OF 1 LEAFSPOT FUNGICIDES ON PEANUTS Gallons of water per acre Infection Pct. 60.2 Defoliation Pct. 42.2 Yield/acre Lb. 3,377 5 ---------------------------------------- - ----10 ------------------ ----------------------------15 20 -. --.. . 63.4 58.6 59.7 44.6 43.4 40.5 3,338 3,487 3,266 . ..- 1 Data represent mean of Benlate, Bravo, and Kocide delivered at 60 p.s.ithrough hollow cone nozzles, three nozzles per row. IMPROVEMENT OF BRAVO (CHLOROTHALONIL) PERFORMANCE Beginning in 1974 efforts were made to find a more effective Bravo fungicide formulation to permit a reduction in the amount of product used per acre. Some success was achieved earlier when the '6F' formulation was found to be more effective than the former Bravo 75WP. This study was undertaken to determine: (1) is wet-milled Bravo superior to air-milled for achieving a smaller particle size, (2) are wet-milled preparations superior in control of peanut leafspot, and (3) what physical parameters other than particle size affect disease control? Flowable formulations of chlorothalonil were prepared by wet- PEANUT LEAFSPOT RESEARCH IN ALABAMA 27 mill grinding of technical Bravo in the flowable matrix. Grinding was achieved by the shearing action of metal balls rotating under pressure in a steel chamber (attriter). Samples were removed after 3, 9, and 13 hours, adjusted to 54 percent active ingredient (w/v), and particle size and distribution determined with a Coulter model TA-2 counter equipped with a 30-pm orifice. Median particle size, total surface area per gram, and numbers of particles per gram of active ingredient were estimated assuming a spherical particle shape. In 1974, wet-milled formulations were compared to commercial air-milled formulation (Bravo 6F) for physical properties and for field performance. The same procedure was used in 1975, but a wet-milled sample was selected that had physical parameters similar to that of the standard air-milled product. A second wet-milled sample that had a mean particle size approaching that found to be most effective in 1974 was also tested in 1975. Fungicidal performance was evaluated in 1974 and 1975 on peanut field plots for control of early and late leafspot. Experiments were conducted with rates of 0, 0.5, 1.0, and 1.5 pints per acre of formulated ingredient for each formulation, delivered in a spray volume of 14 gallons per acre at a pressure of 60 p.s.i. In addition, a rate of 0.75 pint per acre of each formulation was tested during the 1975 season. Each plot consisted of four 50-foot rows spaced 3 feet apart. The first spray was applied approximately 45 days after planting and was repeated at 14-day intervals for a total of seven applications. Leafspot disease evaluations and yields were obtained by methods described earlier in this bulletin. Field plots were in a randomized complete block design. The inherent factorial arrangement permitted development of Duncan's multiple range comparisons (19) of formulation means, rate means, and treatment means. Preparations of air-milled and wet-milled chlorothalonil used in 1975 were suspended in water and filtered onto a Millipore filter membrane (0.22- m pore size), dried at 40 0 C for 10 hours, shadowed with gold, and viewed and photographed on an AMR model 1000 scanning electron microscope to determine particle surface configuration and size. Coulter counter analyses of wet-milled chlorothalonil preparations and the standard air-milled product indicated that wetmilling (WM) produced a more finely divided product than did 28 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 20. LEAFSPOT INFECTION AND DEFOLIATION OF FLORUNNER PEANUTS TREATED WITH VARIOUS RATES AND FORMULATIONS OF 54 PERCENT FLOWABLE BRAVO, 1974 Percent defoliation,1,2 by formulation rate3/acre Formulation Air-milled Wet-milled 3 hours 9 hours 13 hours Rate mean 0.5 pt. .--------- 59.0 b 1.0 pt. 42.3 cde 41.4 32.6 34.2 37.6 def gh fgh Y 1.5 pt. 32.2 ghi 25.1 21.0 27.8 25.3 hij Formulation mean 44.5 A 40.8 AB 34.6 B 35.2 B 3 ----------- --------..... 56.0 bc --------- 50.1 bcd 48.6 cde ........--------53.4 X j ij Z Percent infection,1,2 by formulation rate /acre 0.5 pt. Air-milled 39.2 b Wet-milled 32.9 bc 3 hours 9 hours .....--------- 31.5 cd ____________ cde 27.2 13 hours..... Rate mean ......--------- 32.7 X ------- 1.0 pt. 24.5 def 23.9 17.2 22.9 22.1 ef fgh egh Y 1.5 pt. 19.0 fgh 15.5 14.1 15.4 16.0 gh h gh Z Formulation mean 27.6 A 24.1 A 20.9 B 21.8 B 1 Control value = 73.8 percent infection and 50.4 percent defoliation. 2 Values followed by different letters (lower case) are significantly different at the 5 percent level using Duncan's Multiple Range Test; mean values followed by different upper case letters are significantly different. 3 Active ingredient rate per acre. air-milling. Near minimal particle size and maximal surface area were achieved after 9 hours. Results revealed that the 9-WM and 13-WM preparations generally were more effective than the standard product air-milled in reducing peanut leafspot infection and defoliation, Table 20. Furthermore, results indicated that rates of 1 pint per acre of 9-WM were as effective as 1.5 pints of the standard air-milled product. The 3-WM, with a larger median particle size, less total surface area, and fewer particles per gram, consistently controlled disease better than the air-milled formulation (1,6). Evaluation of 1975 disease control data confirmed results obtained in 1974, Table 21. Again, disease control from the finely ground, wet-milled preparation applied at rates between 0.75 and 1.0 pint per acre was equivalent to the standard product air-milled applied at a rate of 1.5 pints per acre. The wet-milled standard, with particle size and surface area similar to that found for the air-milled, was significantly more effective than the air-milled product in controlling disease. Peanut yield data (not presented) indicated significant differences (P < 0.05) and these were inversely related to disease incidence in both 1974 and 1975. PEANUT LEAFSPOT RESEARCH IN ALABAMA 29 TABLE 21. LEAFSPOT INFECTION AND DEFOLIATION OF FLORUNNER PEANUTS TREATED WITH VARIOUS RATES AND FORMULATIONS OF 54 PERCENT FLOWABLE BRAVO, 1975 Percent infection', Formulation by formulation rate,/acre 2 Formu- 0 ab ab a W 0.5 pt. 56.5 56.2 49.0 53.9 abc abc cde X 0.75 pt. 54.6 44.2 45.8 48.2 bc def def Y 1.0 pt. 50.4 43.7 37.4 43.8 cd def fgh Y 1.5 pt. 41.6 35.3 31.4 36.1 efg lation mean 52.9 A 48.4 B 45.6 B 2 Air-milled .........------61.2 62.8 Wet-milled _ Wet-milled (fine) 64.6 -_ 62.9 Rate mean gh h Z Percent defoliation, by formulation rate/acre 0 Air-milled ...........------38.7 Wet-milled ..-..... 39.0 Wet-milled (fine) 37.0 Rate mean ........ 38.2 a a ab A 0.5 pt. 35.1 35.1 31.5 33.9' abcd abc bcd B 0.75 pt. 33.4 29.7 30.6 31.3 abcd cd bcd B 1.0 pt. 33.5 27.7 29.4 30.2 abcd d cd BC 1.5 pt. 26.9 27.7 26.6 27.1 d d d C Formulation mean 33.5 X 31.8 X 31.0 X 1 Values followed by different letters (lower case) are significantly different at the 5 percent level using Duncan's Multiple Range Test; mean values followed by different upper case letters are significantly different. 2 Active ingredient rate per acre. Scanning electron micrographs of air-milled and wet-milled chlorothalonil preparations revealed that the wet-milled sample contained somewhat more fractured, angular, and smaller-sized particles than did the air-milled sample. In addition, major differences in the distribution were apparent. Use of the Coulter counter provides plot data on particle size distribution not available in 1950. The resultant "profiles" developed here demonstrate visually how various particle-size blends may result in improved performance of many water-insoluble fungicides, Figure 1 and Figure 2. The resultant decrease in rates required for disease control could significantly reduce the total pesticide load in agricultural areas. Whether Bravo activity is most affected by the distribution of particle sizes or surface configuration of particles was not determined. Regardless, formulations should have smaller particles with a reserve of larger particles to weather down continually to the more biologically active small particles. Three physical factors relating the nature of chlorothalonil particles in the Bravo formulation to fungicidal efficacy were determined in this study: (1) particle size; (2) the distribution of particle sizes, and (3) surface configuration of the individual par- 30 ALABAMA AGRICULTURAL EXPERIMENT STATION A 15 Air - milled standard Median diam. = 3.30 ,um 2 Surface area = .1.31 x 10 pm/g Particle no. = 2.38x IOi/g 15 B 15 SParticle ° Wet-milled 3 hours Median diam. =3.8 jum 2 Surface area = 1.35 x 10'upm /g no. = 3.44 x.10/g 10 5 0 C a 15 Wet-milled 9 hours Median diam. - 1.75 SParticle pm 2 Surface area = 2.17 x 1012pm /g no.7.53 x /g 0- C D 15 I I I I I I " / 10 5 0.5 0Particle Wet-milled 13 hours Median diam. = .150 pm = Surface area 2.44x 1012pm 1 no. = 8.91 x 01 /g 2 /g 1.0 2.0 Particle diameter 4.0 (pm) 8.0 li FIG. 1. Effects of air-milling (commercial formulation) and wet-milling of technical chlorothalonil on particle-size distribution of 1974 samples. ticles. The standard air-milled formulation affects only particle size advantageously, while wet-milling improves chlorothalonil efficacy through all three components. The results of this study convinced Diamond Shamrock Corporation of the improved performance of wet-milled Bravo 6F. In 1976 all Bravo 6F sold in Alabama was the wet-milled type. Studies will be continued to determine if rates can be reduced from 1976 recommendations. Studies are continuing to evaluate the performance of wet-milled sulfur (Super-6) and other fungicides to further evaluate the potential of this process. PEANUT LEAFSPOT RESEARCH IN ALABAMA 31 PEANUT LEAFSPOT RESEARCH IN ALABAMA 3 A 15 10 Z5 0 Air-milled standard Median.diam. =3.30 jm 2 Surface area 1.29 x l 12 Mm /g 1 1 Particle na.= 2.51 x 10 /g B c 15 U ai Wet-milled standard Median diam.:=3.71 gm Surface area = 1.28 x na.=2.73x 101pm2/g iParticle /g 10 0_ 5- .S C C 15 10 5 0.5 1.0 2.0 4.0 Particle diameter (pm) 8.0 16 Wet-milled fine grind Median diam. = 1.60 Mm Surface area £ 2.47x1 Mm Particle na.= 9.99 x10 /g a /g FIG. 2. Effects of air-milling (commercial formulation) and wet-milling of technical chlorothalonil on particle-size distribution of 1975 samples. WET WEATHER AT HARVEST: WHEN DO YOU DIG? Sometimes needed information is developed purely by accident. Such was the case when Hurricane Eloise passed over experimental plots at the Wiregrass Substation on September 23, 1975. Peanuts in a leafspot control study were mature and ready to be harvested when the hurricane appeared. One-half of each plot was dug the day before the hurricane arrived, and remained inverted and on the ground through the storm. The other half was dug as soon as possible after the storm had passed. The results of this test are shown in Table 22. These data show that most of the peanuts from the delayed final harvest were lost because of senesence and heavy wet soil. Only a few peanuts were lost by digging just before the hurricane, and none of these were found to have Aspergillus flavus (Segregation 3). These data indicate that, should a warning for prolonged wet weather be 32 TABLE 22. ALABAMA AGRICULTURAL EXPERIMENT STATION EFFECT OF HURRICANE ELOISE1 ON PEANUT YIELDS, 1975 Yield, by fungicide and harvest timing Fungicide Dug and harvested Dug before, before hurricane Lb. B ravo - ----------------------------- .......... 3,981 Difolatan ...................................... 4,095 Kocide 404S -------------------------------- 3,615 Duter + S _ ---------- 3,639 Nontreated control ------------------2,970 Digging date ___--------------------------9/12 Harvest date ----------. 9/17 _.-------.......... harvested afterate Lb. 3,761 4,037 2,976 3,528 2,402 9/22 9/30 Dug and harvested after Lb. 2,982 2,950 2,314 2,555 1,226 9/30 10/5 1 Hurricane Eloise passed Headland September 23, 1975. announced, a grower would do better by digging his mature peanuts than by leaving them in the ground until after the wet weather. SUMMARY The data presented here indicate that control of peanut leafspot is a complex matter and that the researcher must evaluate much more than just control of the leafspot fungus. Fungicides were shown to affect soil-borne diseases, kernel quality, and insects, as well as yields. Yields have not always been related to crop value per acre. Appendix 2 lists the fungicides and combinations recommended for control of peanut leafspot. These recommendations reflect most of the information developed since 1970 and presented in this bulletin. Experiments are continuing to develop control systems that will require less time, equipment, and money. Should peanut prices revert to the world market price, economy in disease control will be necessary for profitable farm operation. Appendix 3 illustrates the progress made in peanut yields and crop value in the past 15 years. Only through continued research can these curves continue their upward trend. PEANUT ' LEAFSPOT RESEARCH IN ALABAMA 33 PEANUT LEAFSPOT RESEARCH IN ALABAMA 33 REFERENCES (1) BAcKMAN, P. A., G. D. MUNGER, AND A. F. MARKS. 1976. The Effects of Particle Size and Distribution on the Performance of the Fungicide Chiorothalonil. Phytopath. 66:1242-1245. (2) J. R. RODRIGUEZ-KABANA, --------------------- AND C. WILLIAMS. 1975. The ,--Effect of Peanut Leafspot Fungicides on the Non-target Pathogen, Scierotium rolfsii. Phytopath. 65:773-776. (3) BERGER, R. D. 1973. Infection Rates of Benomyl Resistant Cercospora spp. Abstract No. 0156 in Abstracts of Papers, Second nt. Cong. Plant Pathol. September 5-12, Minneapolis, Minn. (unpaged). (4) -------------------------of 1973. Disease Progress . Cercospora apii Resistant to Benomyl. Plant Dis. Rep. 57:837-840. (5) BUcHENAUER, H. D., G. ERWIN, AND N. T. KEEN. 1973. Systemic Fungi- cidal Effect of Thiophanate Methyl on Verticillium Wilt of Cotton and its Transformation to Methyl 2-benzimidazolecarbamate in Cotton Plants. Phytopath. 63:1091-1095. (6) BURCHFIELD, H. P. AND G. L. MCNEW. 1950. Mechanism of Particle Size Effects of Fungicides on Plant Protection. Contrib. Boyce Thompson Inst. 16:131-161. (7) CLARK, E. M., P. A. BACKMAN, AND R. RODRIGUEZ-KABANA. 1974. Cerco spora and Cercosporidium Tolerance to Benomyl and Related Fungi- cides in Alabama Peanut Fields. Phytopath. 64:1476-1477. (8) CLEMONS, G. P. AND H. D. SISLER. 1969. Formation of a Fungitoxic De- rivative from Benlate. Phytopath. 59:705-706. (9) FEICHTMEIR, E. F. 1949. The Effect of Particle Size and Solubility of Sulfur in Carbon in Carbon Disulfide upon its Toxicity to Fungi. Phytopath. 39:605-615. (10) GARREN, K. H. 1959. The Stem Rot of Peanuts and its Control. Va. Agr. Exp. Sta. Tech. Bull. 144. 59 p. (11) ----------------1973. Studies on Sclerotium rolfsii in the Southeast United States. In the Relationship of Soil Microorganisms to Soilborne Plant Pathogens. Sou. Coop. Ser. Bull. 183, Va. Polytech. Inst. and State Univ. 98 p. (12) GREENE, G. L. AND D. W. GORBET. 1973. Peanut Yields following Defoliation to Assimilate Insect Damage. J. Am. Peanut Res. Educ. Assoc. 5:141-142. (13) GEORGOPOULOS, S. G. AND C. DOVAS. 1973. A Serious Outbreak of Strains of Cercospora Beticola Resistant to Benzimidazole Fungicides in Northern Greece. Plant Dis. Rep. 57:321-324. (14) HAMMOND, J. M., P. A. Peanut Sci. 3:70-72. BACKMAN, AND J. A. LYLE. 1975. Peanut Foliar Fungicides: Relationships between Leafspot Control and Kernel Quality. 34 ALABAMA AGRICULTURAL EXPERIMENT STATION (15) HORSFALL, J. G. 1956. Principles of Fungicidal Action. Chronica Botanica. Waltham, Mass. 280 p. (16) MARTIGNONI, M. E. 1955. Microinjector Needle for Determination of per os-LD5 0 of Insect Viruses. Science 122:764. (17) RODRIGUEZ-KABANA, R., P. A. BACKMAN, AND J. C. WILLIAMS. 1975. Determination of Yield Losses to Sclerotium rolfsii in Peanut Fields. Plant Dis. Rep. 59:855-858. (18) SCHNEIDER, R. W., J. B. SINCLAIR, AND, R. J. WILLIAMS. 1973. Induced Conidial Production of Cercospora spp. Abstract No. 0156 in Abstracts of Papers, Second Int. Cong. Plant Pathol. September 5-12, Minneapolis, Minn. (unpaged). (19) SNEDECOR, G. W. AND W. G. COCHRAN. 1967. Statistical Methods. 6th ed. The Iowa State University Press, Ames. 593 p. (20) U. S. DEPARTMENT OF AGRICULTURE, AGRICULTURAL MARKETING SERVICE. 1973. Farmers Stock Peanuts Inspection Instructions. Washington, D.C., 37 pp. APPENDIX 1 List of Trade, Chemical, and Common Names for Fungicides in Text Trade name 1. Benlate 50 WP 2. Manzate 200 Dithane M-45 3. Kocide 101 (WP) 4. Kocide 404 (F) 5. Kocide 404-S (F) 6. Difolatan 4F 7. Du-Ter 47WP 8. Bravo 6F -9. m z c Common name benomyl mancozeb copper hydroxide Chemical name methyl 1- (butylcarbamoyl) -2-benzimidazole-carbamate coordination product of zine & manganese ethylenebisdi thiocarbamate cuprous hydroxide cuprous hydroxide cuprous hydroxide + sulfur cis-N- (1,1,2,2-tetrachloroethylthio) -4-cyclohexene-l,2dicarboximide triphenyltin hydroxide tetrachloroisophthalonitrile copper ammonium carbonate (exact formula unknown) 1,2 Bis (3-methoxycarbonyl-2-thioureido) benzene u*1I m H rI copper hydroxide copper hydroxide captafol fentin hydroxide chiorothalonil copper ammonium carbonate thiophanate methyl bayleton sulfur (wet-mill) delsan ± manzate mo Oxycop 8L Copper-Count-N 10. Topsin-M 7OWP 11. Bay Meb 6447 5OWP 12. Super-6 (F) 13. DPX-112 14. DPX-1 10 1- (4-chlorophenoxy) -3-3 dimethyl-1- (1H-l,2,4-triazoll-yl) -2 butanone elemental sulfur methyl benzimidazolecarbamate ± manzate 200 methyl benzimidazolecarbamate + sulfur Continued lw delsan ± sulfur W 0% List of Trade, Chemical, and Common Names for Fungicides in Text (continued) Trade name 15. Fungisperse 16. SN-513 (GTA) 17. EL 222 (Bloc) Common name copper sulfate Chemical name copper sulfate ± sulfur 9-aza-l,l7 diguanidinoheptadecane triacetate a (2-cllorophenyl) -a- (4-chlorophenyl) 5 pyrimidene methanol a- (2-florophenyl) -a- (4-florophenyl) rer + sulfur r guazatine triacetate fenarimol nuarimol copper ammonium carbonate + sulfur daminazole 72 second summer oil 18. EL 228 19. Oxycop LS 20. Kylar (hormone) 21. Oil -5-pyrimidene- hI- methanol copper ammonium carbonate ± sulfur succinic acid 2,2-dimethyihydrazide parafrinic series oil e-I C C 7- m x m m z -I 0 z7 PEANUT LEAFSPOT RESEARCH IN ALABAMA 37 APPENDIX 2 Leafspot Disease Control Recommendations (1977) Fungicides Bravo 6F Amount of formulated fungicide to use per acre 112 pints Difolatan 4F Du-Ter 47 WP Du-Ter 47 WP + Micronized Sulfur Du-Ter 47 WP + Flowable Sulfur 6 lb./gal. Kocide 404 S Kocide 404 + Micronized Sulfur Kocide 404 + Flowable Sulfur 6 lb./gal. 3 pints 6 ounces 6 ounces + 1.5 pounds 6 ounces + 1.0 quart 2 quarts 2 quarts + 1.5 pounds 2 quarts + 1.0 quart Always follow these suggestions: 1. Apply fungicides on a 10-14 day schedule. In fields under continuous peanut production or during periods of high rainfall, benefits may be obtained by reducing the spray intervals to as little as 7 days. 2. Inspect peanut fields closely for signs of leafspot to determine the proper time to initiate fungicide applications. The first fungicide application should begin at the first sign of leafspot or no later than when peanuts are 6 inches across in any direction (45-50 days after planting). 3. For the first fungicide application, open only the nozzle directly over the row and leave the two side nozzles closed. At this early stage of peanut development, one nozzle will provide ample spray coverage. The tank mix concentration will be the same concentration used in subsequent fungicide application. However, since only one of the three nozzles is open, approximately 1/3 the normal spray volume per acre will be delivered during this first application. 4. In subsequent sprays when the vines are greater than 12 inches in diameter, use 3 nozzles per row adjusted to give broadcast fungicide application. Correct nozzle height to 18-20 inches over the tops of "center" vines. Direct side nozzles for best coverage. 5. Broadcast fungicide application should be made with 10 to 15 gallons of water per acre. 6. Pressure should be adjusted somewhere between 60 and 80 p.s.i. 7. When Bravo, Difolatan, or Duter are applied, a 14-day waiting period is necessary before peanuts may be harvested. Do not allow livestock to graze treated areas. Do not feed hay from treated fields to livestock. 8. Do not mix Duter with Toxaphene since leaf burning may occur. 9. There are no limitations on sulfur and copper fungicides. 38 ALABAMA AGRICULTURAL EXPERIMENT STATION APPENDIX 3 Contributions of Plant Pathology to Peanut Production Year Contributions of plant pathology to peanut production are illustrated by curves showing steadily increasing yield and value per acre of peanut production. The letter designations indicate the time of practices being adopted or fungicides becoming available for farm use: A-organic fungicides for leafspot control; B---second generation fungicides for leafspot; C-nematicides adopted; and D--soil fungicides for white mold. !\ULLFKN UNIVERSITY With an agricultural unit in exerv major soil area, \uhurn Unieirsity serxes the research needs of field crop, livestock, forestry, arnd horticultural pioducers in each region in Alabama. Evierx citizen of the State has a stake in this reserch program, since any advaiitage fromn ew and "0" more 0 - 0 economical wax s of prodlucinig and hanlinli farm prolucts directly benefits tie consumiig public. i 2 Research * 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. i- Unit Identification -, A Tennessee Volley Substation, Belie Mina. Sand Mountain Substation, Crossville. North Alabama Horticulture Substation, Cullman. Upper Coastal Plain Substation, Winfield. Forestry Unit, Foyette County. Thorsby Foundation Seed Stocks Farm, Thorsby. Chilton Area Horticulture Substation, Clonton. Forestry Unit, Coosa County. Piedmont Substation, Camp Hill. Plant Breeding Unit, Tallassee. Forestry Unit, Autauga County. Prattville Experiment Field, Prattville. Block Belt Substation, Marion Junction. Lower Coastal Plain Substation, Camden. Forestry Unit, Barbour County. Monroeville Experiment Field, Monroeville. Wiregrass Substation, Headland. Brewton Experiment Field, Brewton. Ornamental Horticulture Field Station, Spring Hill. Gulf Coast Substation, Fairhope.