CIRCULAR 267 Comparisons of Methods of Application for Pendimethalin (Prowl 4EC) in Combination with Other Selected Herbicides for Weed Control in Cotton AUGUST 1983 ALABAMA AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY A. BUCHANAN, DIRECTOR AUBURN UNIVERSITY, ALABAMA GALE CONTENTS Page INTRODUCTION............................................... METHODS AND MATERIALS.................................... RESULTS.................................................... 3 5 6 Pendirnethalin (Prowl 4EC).......................... Pendimethalin + Fluometuron (Prowl 4EC + 6 9 + Cotoran 8OWP)................................... Pendimethalin ± Cyanazine (Prowl 4EC Bladex 8OWP).................................... Pendimethalin + 9 + Diuron (Prowl 4EC Karmex 8OWP)................................... Pendimethalin + Norfiurazon (Prowl 4EC + Zorial 80 WP).................................... Pendimethalin +Perfluidone (Prowl 4EC + DeStun 5OWP)................................... SUMMARY................................................... 10 11 11 12 FIRST PRINTING 4M, AUGUST 1983 Information contained herein is available to all persons without regard to race, color, sex, or national origin. COMPARISONS OF METHODS OF APPLICATION FOR PENDIMETHALIN (PROWL 4EC) IN COMBINATION WITH OTHER SELECTED HERBICIDES FOR WEED CONTROL IN COTTON TED WHITWELL, GLENN WEHTJE, , 12 and JOHN A. McGUIRE INTRODUCTION COTTON IS VERY SENSITIVE to weed competition during the early portion of the growing season. In Alabama, plots infested with mixed populations of annual broadleaf and grass weeds yielded less than 15 percent as much as weed free checks. In addition, maximum yields were obtained when the crop was maintained weed free for approximately 8 weeks after emergence . Tremendous change has occurred in weed control since hand hoeing and mule-powered cultivation were the only alternatives. Substituted ureas were among the earliest herbicides to be widely used for preemergence weed control in cotton. Monuron (CMU) became available in 1952. Diuron (first called Weed Killer D, and later Karmex) was introduced as a more effective replacement in 1956. Chloro-IPC or chlorpropham, a phenyl carbamate introduced in 1956, was also used for preemergence weed control. In general, these early herbicides were most effective in controlling annual grasses 'Respectively, Scientist-Weed Control (joint employee with Cooperative Extension Service); Assistant Professor, Department of Agronomy and Soils; and Associate Professor, Department of Research Data Analysis. Research reported was initiated by Gale A. Buchanan, now Dean and Director. 2 The authors acknowledge the assistance of W. B. Webster and Vaughn H. Calvert II of the Tennessee Valley Substation in this project. 3Buchanan, G.A. and C.G. McWhorter. 1971. Weed Control & Cotton. FAO Conference Weed Science Society of America Monographs 1:63-183. and small-seeded broadleaf weeds. Rainfall was a prerequisite for activation; consequently, performance was often variable among years. Consistency of weed control was markedly improved with the introduction of trifluralin (Treflan), the first dinitroaniline (DNA) herbicide. Several other DNA herbicides entered the market soon thereafter. These herbicides are characterized by negligible water solubility and rapid loss due to volatilization from the soil surface. Consequently, incorporation into the soil is usually necessary. Weed seed germinating within this treated soil generally absorb lethal amounts of herbicide. Crop injury is minimized by planting the crop seed beneath or near the bottom of the treated soil layer, allowing developing roots to pass quickly into untreated soil. Preplant incorporated (PPI) applications of DNA herbicides provided more consistent performance compared to earlier materials. Annual grasses and other weeds, including seedling johnsongrass and small seeded broadleaf weeds such as pigweed, purslane, and carpetweed, were effectively controlled. Application of twice the normal use rate was also effective in reducing rhizome johnsongrass infestations. Subsequent to introduction of DNA's, other herbicides have been added to the weed control arsenal for use in cotton. Some of these provide effective preemergence control of largeseeded broadleaf species. For example, fluometuron (Cotoran), introduced in 1965, provides acceptable control of common cocklebur and annual morningglories. A herbicide to control all weeds with no adverse effect on cotton has not yet been developed. Achieving optimum control with current technology invariably requires that combinations, or systems, of herbicides be used which are more or less specific for the predominate weed species. Systems in which a DNA herbicide is first applied preplant incorporated (PPI), followed by a preemergence application of a second herbicide, are very popular. While this practice (termed overlay) provides a good weed control, two separate herbicide applications are required. It would be economically advantageous if both materials could be applied as a single PPI or PRE treatment. Within the DNA herbicides currently registered in cotton, pendimethalin (Prowl) has one of the highest water solubilities, and is one of the least susceptible to vapor loss. [4] Therefore, comparable weed control should be achieved with or without immediate incorporation. The objective of this study was to compare weed control as provided by pendimethalin in combination with several other commonly used herbicides, applied as either a single PPI or PRE treatment or as separate applications in the manner of an overlay. METHODS AND MATERIALS Trials were conducted at the Tennessee Valley Substation, Belle Mina, Alabama, between 1978 and 1980. Soil type was a Decatur clay loam. The test site was turned with a moldboard plow each winter and subsequently disked and smoothed during early April with a Lely Rotera R. Pendimethalin alone and pendimethalin combined with each of five herbicides, table 1, were applied three ways: (1) PRE, (2) PPI, and (3) as an overlay (OL) in which pendimethalin was applied PPI and the other material applied PRE. Rates used were those which the manufacturers recommend for the soil type. Untreated checks were also included. Herbicide treatments were assigned to plots which were four rows wide and 20 feet long, and replicated four times in a randomized complete block design. All treatments were applied broadcast in 15 to 18 gallons per acre of water with a tractor-mounted compressed air sprayer. When necessary, incorporation was accomplished with two parallel passes with a Lely Roterra R which proyided uniform incorporation to a depth of 11/2 inches. Cotton (Stoneville 213) was planted between April 10 and 20 of each year. Two rows in each plot were cultivated and hand weeded as necessary to provide complete weed control. Therefore, any reduction of yield within a plot could be attributed to crop injury due to herbicides. The remaining two rows were not TABLE 1. HERBICIDES WHICH WERE EVALUATED FOR WEED CONTROL IN COTTON AT Trade name Rate active Rate product Herbicide family THE TENNESSEE VALLEY SUBSTATION, BELLE MINA, ALABAMA, 1978-1980 Common name Lb./acre Pendimethalin Fluometuron Cyanazine Diuron Perfluidone Norflurazon Prowl 4EC Cotoran 80WP Bladex 80WP Karmex 80WP Destun 50WP Zorial 80WP 0.75 1.50 1.25 1.00 3.00 1.50 Per acre 1.50 1.88 1.56 1.25 6.00 1.88 pints lb. lb. lb. lb. lb. Dinitroaniline Substituted urea Triazine Substituted urea Unclassified Unclassified [5] TABLE 2. PREDOMINANT ANNUAL WEED SPECIES IN COTTON, TENNESSEE VALLEY SUBSTATION, BELLE MINA, ALABAMA Weed Redroot pigweed (Amaranthus retroflexus L.) Pitted morningglory (Ipomoea lacunosa L.) Prickly sida (Sida spinosa L.) Fall panicum (Panicum dichotomiflorum Michx.) Large crabgrass [Digitariasanguinalis (L.)Scop.] Type Small seeded broadleaf Large seeded broadleaf Large seeded broadleaf Grass Grass cultivated so that any weed control achieved could be attributed solely to the herbicide treatment. Fertilization and insect control measures were based on soil test results and the recommendations of field scouts, respectively. Ratings on the level of crop injury and control of the pertinent weed species, table 2, were taken 6 to 8 (early) and 12 to 14 weeks (late) after planting. A rating of 80 or above is generally considered to be commercially acceptable; 90 and above is considered excellent. All plots were mechanically picked twice and the total yield determined. RESULTS Performance of all herbicide treatments in terms of weed control was sufficiently uniform over the 3 years of evaluations (as indicated by statistical analysis) so only the 3-year-average ratings needed to be examined. Both cultivated and noncultivated yield for all years are presented. Pendimethalin (Prowl 4EC) Fall panicum was the only weed for which pendimethalin applied alone provided "excellent" control through the final rating, table 3. Control of this weed was not affected by method of application. Early season control of large crabgrass was excellent applied PPI, but only "good" if applied PRE. Pendimethalin provided good early season control of redroot pigweed. However, control fell below 80 percent by the second rating. Control of pitted morningglory and prickly sida was poor with pendimethalin alone, indicating its lack of activity on large-seeded broadleaf species. No crop injury could be detected with pendimethalin alone. Noncultivated yields, table 4, were significantly lower in all years than yields from some of the more successful combinations (i.e., pendimethalin + fluometuron). In all years, cultivation markedly enhanced yields due to improved weed control. [6] TABLE 3. WEED CONTROL 1 AND CROP INJURY 2 RATINGS FOR PENDIMETHALIN AND PENDIMTHALIN COMBINATIONS AS AVERAGED OVER ALL METHODS OF APPLICATION 1978-1980 AVERAGE Herbicide(s) Pendimethalin Pendimethalin + flurometuron Pendimethalin + cyanazine Qendimethalin + diuron Pendimethalin + norflurazone Pendimethalin+ perfluridone Checks 1 Redroot pigweed Early Late 85b 78b 98a 99a 96a 98a *99a 99a Oc *83b 93a 96a 95a 11c Pitted morningglory Early Late 15d 62c 96a 93a 88b 86b 88b 90ab Od *39bc 27c 46b 33bc Oe Percent weed control by species 3 Prickly Fall sida panicum Early Late Early Late lid 95b 93bc 43d 99a 98a 93a *90a 88b *79c *96a *86b Oe 48b 33c 86a *28c Od 100a 98ab 99a *97ab 8c 96ab *89c *97ab 95ab 4d Large crabgrass Early Late *88d 71c 94ab *98ab 96bc *94c 100a 100a 3e *85b *75c *97a 96a 7d Cropinjury Early Late oa la 3a Oa 3a 3a *7b *29c Oa Oa Oa Oa *8b Oa Rating of 80 or above is generally considered commercially acceptable, and 90 or above is considered excellent. 20-19 = none to slight, 20-69 = moderate, 70-99 = severe, 100 = death. Means within a column followed by same letter are not significantly different at the 5 percent probability level. 3 Means within a column followed by same letter are not significantly different at the 5 percent probability level. *Signifies that method of application resulted in significant differences in this average value. TABLE 4. HERBICIDE COMBINATIONS FOR WHICH METHOD OF APPLICATION PRODUCED SIGNIFICANT DIFFERENCES IN CONTROL OF CERTAIN WEEDS AS INDICATED BY LATE SEASON RATING, 1978-1980 AVERAGE Percent weed control, Pendimethalin + Pendimethalin + 2 Pendimethalin + Pendimethalin + Method of application flurometuron Prickly sida 97a 93ab cyanazine Large Redroot pigweed crabgrass diuron Fall panicum Large crabgrass Fall 100a 98a norflurazon Large crabgrass panicum Preemergence Overlay Preplant incorporated 'Rating of 80 or above is 2 Means within a column 72b 89a 82b 94a 92a 97a 75a 91a 99a 100a 93b 59b 93b 79b 88a 79b 79b generally considered commercially acceptable and 90 or above is considered excellent. followed by same letter are not significantly different at the 5 percent probability level. o00 TABLE 5. SEED COTTON YIELDS ACHIEVED FROM PENDIMETHALIN AND PENDIMETHALIN COMBINATIONS AS AVERAGE OVER ALL METHODS OF APPLICATION Treatment Cult. Lb. 2,130ab 2,050b Pendimethalin Pendimethalin + flurometuron 2,210ab 1,800b 2,340a 2,240a *2,010b 2,580a *2,210b Pendimethalin + cyanazine Pendimethalin + 2,280a 1,900b 2,600a *1,830c 2,280a *1,850b 2,390a diuron 2,320a 2,120ab 2,550a 2,250b 2,190ab 2,030b Pendimethalin + 2,230ab norflurazon *1,670b *1,630cd 1,250c 890c 1,410c Pendimethalin + 1,300c 1,110d perfluradone 490d 2,190b 2,350a 620e 2,080b 2,150ab 710e Check 1Means within a column followed by same letter are not significantly different at the 5 percent probability level. 2Signifies that method of application resulted in significant differences in this average value. 1978 Noncult. Lb. 1,410c 2,290a Cult. Lb. 2,430a 2,530a Seed cotton yield'/acre 1980 1979 Noncult. Noncult. Cult. Lb. Lb. Lb. 0 1,510d 2,080b 1,110c 2,360a 2,580a 2,310a Cult. Lb. 2,210b 2,300ab Average Noncult. Lb. 1,340d 2,410a 2,010b *1,760c 2,130b 1,210d 600e Pendimethalin + fluometuron (Prowl 4EC + Cotoran 80WP) This combination provided excellent (90 percent) full season control of all pertinent weeds, table 3. PRE and OL applications were generally rated superior to PPI. However, only in the late season rating of prickly sida was the PRE application measurably superior (p < 0.05) to the PPI, table 5. Overlay application provided intermediate control. Slight (although statistically unmeasurable) early season crop injury was detected primarily with the PRE and OL applications. The crop quickly recovered and no injury was visible by the later rating regardless of method of application. Yields from this herbicide combination were consistently among the highest of the entire experiment, table 4. The 3year-average seed cotton yield with and without cultivation was nearly identical, reflecting the wide range weed control and excellent crop safety of this combination. Under no circumstances could a difference in yield be attributed to the method of herbicide application. Pendimethalin + Cyanazine (Prowl 4EC + Bladex 80WP) This combination provided excellent early season control of redroot pigweed, fall panicum, and large crabgrass regardless of the means of application, table 3. Control of fall panicum remained excellent through the late rating regardless of method of application. Late season control of crabgrass remained in the excellent category only with OL application; with either PPI or PRE application, control dropped significantly over the course of the season, table 5. Likewise, control of redroot pigweed dropped substantially between the early and late ratings. Drop in control was greatest with preemergence application. These results were expected since TABLE 6. HERBICIDE COMBINATIONS FOR WHICH IN SOME YEARS METHOD OF APPLICATION PRODUCED SIGNIFICANT DIFFERENCES IN NONCULTIVATED YIELD OF SEED COTTON iMethod of Seed cotton yield'/acre Pendimethalin + diuron Pendimethalin + cyanazine 1978-80 av. 1979 1979 1980 1978 Lb. 1,870b Preemergence 1,810b Overlay 2,350a Preplant incorporated 'Means within a column followed percent probability level. Lb. 2,010b 2,610a 2,000b Lb. 1,710b 2,200a 1,580b Lb. 2,080a 2,180a 1,280b Lb. 1,880a 2,120a 1,570b by same letter are not significantly different at 5 [9] cyanazine is a short-lived herbicide. In general, the OL application provided greatest longevity of control. Noncultivated seed cotton yield, averaged over all 3 years, was 2,010 pounds per acre, which is significantly lower than what was achieved with pendimethalin + fluometuron. This reflects limited control of the total weed spectrum and the short duration of activity of cyanazine. In 1978, yields resulting from PPI were significantly greater than other OL or PRE applications, table 6. OL application produced the highest yields in 1979. However, in the 3-year average no yield differences could be attributed to method of application. In all years, cultivation enhanced yield. Pendimethalin + Diuron (Prowl 4EC + Karmex 80WP) This combination provided excellent season-long control of redroot pigweed, fall panicum, and large crabgrass, table 3. However, control was strongly influenced by method of application. This trend was especially evident in the late season rating of grass weeds. PPI application resulted in significantly less control of both fall panicum and large crabgrass than either PRE or OL applications, table 5. Substituted urea herbicides, which include diuron, are known to lose activity when incorporated into soil because of excessive soilherbicide binding. Early season control of pitted morningglory was acceptable with all methods of application; however, late season control was poor regardless of application method. Acceptable early season prickly sida control was obtained with PRE and OL but not with the PPI application. Late season control was poor with all methods. Noncultivated yields from this combination were significantly less than what was obtained with pendimethalin + fluometuron, table 4. In all years, cultivation enhanced yield. Again, this reflects incomplete control of the weed spectrum. Pendimethalin + diuron was the only combination in this study where the means of application affected the 3-yearaverage noncultivated yield. In 2 of the 3 years (and with the combined average), yield from PPI application was significantly less than from OL application, which was consistently superior. [10] Pendimethalin + Norflurazon (Prowl 4EC + Zorial 8OWP) This combination provided excellent season-long control of redroot pigweed, fall panicum, and large crabgrass regardless of method of application, table 3. PRE application provided excellent full season control of prickly sida. This combination produced significantly greater early season crop injury than any other combination tested except pendimethalin + perfluridone. Injury was significantly greatest with PRE application; however, by the late rating, no injury was detectable regardless of means of application. Average noncultivated seed cotton yield for the 3-year period was 2,130 pounds per acre, table 4. This is significantly lower than yields obtained with pendimethalin + fluormeturon. In all years, cultivation enhanced yields approximately 100-300 pounds per acre, which reflects incomplete control of the weed spectrum. In no year could a significant difference in yield be attributed to method of application, nor could any trends be identified. Pendimethalin + Perfluidone (Prowl 4EC + Destun 50WP) 4 This combination provided excellent full season control of redroot pigweed, fall panicum, and large crabgrass, regardless of method of application, table 3. As evidenced by the late ratings, this combination had no appreciable activity on pitted morningglory or prickly sida. All methods of application resulted in "moderate" (29 percent) crop injury. Injury was significantly greater with OL application. Average yields with and without cultivation were 1,410 and 1,210 pounds per acre, respectively, table 4. These yields, which were the lowest observed in the study (except the noncultivated check), reflect injury from which the crop never fully recovered. Cultivation enhanced weed control in all years. Averaged across all years, method of application had no effect on yield. 4 Destun was removed from the market in 1980 due in part to excessive crop injury. [11 1 SUMMARY Excellent control of each of these weed species, except fall panicum, was attained only with herbicide mixtures. Of the combinations evaluated, pendimethalin + flurometuron was the most effective. Only this combination provided excellent full season control of both pitted morningglory and prickly sida. Pendimethalin + norflurazon was statistically equal to pendimethalin + flurometuron in terms of prickly sida control; however, this combination had no appreciable activity on pitted morningglory. All combinations except pendimethalin + cyanazine provided excellent control of redroot pigweed. However, the addition of cyanazine to pendimethalin provided no greater control than pendimethalin alone. Excellent control of large crabgrass was achieved with pendimethalin + flurometuron or norflurazon regardless of method of application, and with pendimethalin + cyanazine or diuron depending on method of application. The 3-year-average noncultivated yields from pendimethalin ± flurometuron and norflurazon were comparable to the cultural weed-free checks, indicating the superiority of these two combinations. For pendimethalin alone and most pendimethalin combinations, the method of application had no bearing on weed control or crop injury. For a few combinations, notably pendimethalin + fluometuron for control of prickly sida and pendimethalin + diuron for control of fall panicum and large crabgrass, the method of application comprised the difference between acceptable and nonacceptable control. In these cases, an overlay invariably gave the best control. Results demonstrate that in most cases pendimethalin alone or combined with other herbicides, applied as a single PPI or PRE treatment, gave control comparable to separate applications.