DECEMBER 1972 BULLETIN 442 AGRICULTURAL EXPERIMENT R. Dennis Rouse, Director STATION/AUBURN UNIVERSITY Auburn, Alabama r ~ iI INFLUENCE OF SIMULATED EARLY -SEASON INSECT DAMAGE ON GROWTH AND YIELD OF COTTON CONTENTS Page PROCEDURES............ RESULTS AND DISCUSSION 5 5 7 19671968 1969 General Discussion 10 LITERATURE CITED 11 FIRST PRINTING 4M, DECEMBER 1972 Influence Of Simulated Early-Season Insect Damage On Growth And Yield Of Cotton D, JR.' F. R. GILLILAN, early-formed cotton squares have been considered essential for high (flower buds) generally cotton yields. Producers often attribute most early-season square loss to injury from insects such as the cotton fleahopper, Pseudatomoscelis seriatus (Reut.), tarnished plant bug, Lygus lineolaris (P. de B.) and boll weevil, Anthonomus grandisBoheman. However, square abscission can be, and often is, a response to many other factors including drouth, temperature extremes, plant diseases, excessive soil moisture, and hereditary factors (1,5). Fruit shed resulting from physiological stresses, i.e., natural shed, usually is slight early in the season while plants are young, but increases during the season. For a period of time after anthesis begins, flowering will greatly exceed shedding, but later in the season shedding of squares and young bolls may equal or outnumber the flowers produced (1). Several early workers, Eaton (3), Hamner (4), Dunnam et al. (2), showed that early defloration caused no significant reduction in cotton yields, and in some cases they recorded yield increases. However, despite these reports, many still subscribe to the practice of protecting all early-formed squares, regardless of cost. Thus, experiments designed to simulate early-season insect square damage by manual removal of squares were conducted to determine the impact of early-season square loss on growth and yields of modern cotton varieties. D EVELOPMENT AND MATURATION of 'Associate Professor, Department of Zoology-Entomology. 4 ALABAMA AGRICULTURAL EXPERIMENT STATION PROCEDURES These experiments were conducted at the Agricultural Engineering Research Unit near Marvyn, Alabama, in 1967, 1968, and 1969. The basic experimental method employed each year was similar; however, there were some changes each year in test procedures. Square loss in response to insect injury was simulated by manual removal of all squares at weekly intervals for 1 to 6 weeks. Each year treatments were initiated when at least 50 per cent of the plants had at least one easily visible square. This date was arbitrarily selected as the date on which fruiting began. Squares were removed from the plants by pulling, breaking, or pinching the square from the fruiting branch. Care was exercised not to break branches or otherwise injure plants. Squares were removed from Treatment 1 for 1 week, from Treatment 2 for 2 consecutive weeks and so on until Treatment 6 had squares removed for 6 consecutive weeks, Table 1. So that the effects of square loss would not be confounded with insect injury, injurious insect infestations were suppressed to very low levels throughout the test by regular applications of recommended insecticides. In 1967, Coker 413 cotton was used for the test. Plots were planted April 19 in a solid pattern on 40-inch rows. Each treatment was replicated three times in single-row plots 25 feet long. Subsequent to square removal plant height and fruiting were monitored. All plots were hand harvested on November 19. During the picking operation, care was taken to exclude burrs and other extraneous plant matter from the samples. In 1968, Coker 413 cotton was again used for the test. Plots were planted April 18 in the same pattern as 1967. Treatments TABLE 1. DESCRIPTIONS OF TREATMENTS IN SQUARE REMOVAL TEST, MARVYN, ALABAMA Treatment No. 1 2 3 .... 4---------------------------5-------------------------6 7 --------------------------------------All sq. All sq. All sq. All sq. All sq. All sq. C heck Description removed during first week removed at weekly intervals removed at weekly intervals removed at weekly intervals removed at weekly intervals removed at weekly intervals (N o. sq. removed). of for for for for for squaring 2 weeks 3 weeks 4 weeks 5 weeks 6 weeks INFLUENCE OF EARLY-SEASON INSECT DAMAGE 5 were replicated four times in single-row plots 10 feet long. The effect of square loss on plant height was assessed by measuring 25 marked plants in each treatment at weekly intervals for 7 weeks following the first date of square removal. All plots were hand harvested on December 13. In 1969, Auburn 56 cotton was planted on April 22 for the test, using the same planting pattern as the previous 2 years. Each treatment was replicated five times in single-row plots 10 feet long. Twenty-five plants were tagged and measured each week for 6 weeks following the first date of square removal to assess the effects of square removal on plant growth. Plant fruiting subsequent to square removal was assessed by determining the type and number of fruiting structures present on September 8, i.e., 11 weeks after square removal began. Cotton in all treatments was hand harvested on October 17 and November 14. RESULTS AND DISCUSSION 1967 Although some variation in plant height within treatments was observed, the average plant height in all treatments where squares were removed was greater than for plants in the check, Table 2. The increase in plant height was most noticeable in those treatments where square removal occurred for 3 or more weeks. Counts of fruiting structures present 12 weeks after the first date of square removal also show the impact of complete defloration on the cotton plants, Table 3. Plants undergoing comTABLE 2. HEIGHT OF COTTON PLANTS SUBSEQUENT TO EARLY SEASON SQUARE Loss, MARVYN, ALABAMA, 1967 Treatment8/1 Av. plant height' 8/14 8/22 8/28 In. 1 2..... 3 4 5 6 7 2 In. 46 45 48 50 49 46 41 In. 45 47 49 48 50 54 44 In. 47 49 51 48 52 51 46 40 38 43 45 42 38 - 39 SSee Table 1 for description of treatments. Averages based on measurement of 30 plants. 6 TABLE 3. ALABAMA AGRICULTURAL EXPERIMENT STATION NUMBER OF FRUITING STRUCTURES PRESENT 12 WEEKS AFTER FIRST DATE OF SQUARE REMOVAL, MARVYN, ALABAMA, 19671 Treatment' 1--- -------------------------2------------3--------------------4--------------------------------------5--------------------------------------6.--------------------------1 Av. sq./acre No. 0 0 0 7,956 23,920 43,836 - ---------- 7------------------ -- 0 Av. boils/acre 3 No. 75,764 83,200 77,116 76,440 60,476 75,244 65,520 Av. cracked or open boils/acre No. 0 0 0 0 0 0 10,088 Data are based on complete counts of all on 9/12/67. Table 1 for description of treatments. were counted as bolls. fruiting structures in each replicate 2See 'Blooms plete square loss for 5 and 6 consecutive weeks were still developing squares whereas plants in the other treatments were devoid of squares. Boll counts indicated little differences in the number of boils present in all treatments. However, the bolls present in treatments where squares were removed for 5 and 6 weeks were still quite small, while the check and plots where squares were removed for 1 to 4 weeks had larger and more mature bolls. Only the check had bolls that had matured to the open stage. Yield data, Table 4, reflect the immaturity of the bolls found in the plots subjected to square removal for 5 or 6 successive weeks. Although harvesting was delayed until after cold weather had terminated boll maturation, many of the bolls produced by TABLE 4. YIELD OF SEED COTTON FROM SQUARE REMOVAL MARVYN, ALABAMA, 1967 TEST, 1 Tramn Yield per acre replicate'2 ramnt Mean Lb. Lb. 3 Lb. 1---------------------2,132 Lb. 2,366 2,756 2,418 a 2--------------------3--------------------4--------------------5--------------------6--------------------7------------------ _---2,262 1,950 2,548 2,366 1,664 1,170 2,444 2,444 2,314 1,742 1,534 2,392 2,964 2,184 2,678 1,690 1,118 2,470 2,454 a 2,392 a 2,454 a 1,700 b 1,274 b 2,376 a ' See Table 1 for description of treatments. 2 Hand harvested 'Means followed by same letter are not significantly different at the 5 % level. 11/19. INFLUENCE OF EARLY-SEASON INSECT DAMAGE TABLE 5. HEIGHT OF COTTON PLANTS SUBSEQUENT TO EARLY SEASON SQUARE 7 Loss, MARVYN, ALABAMA, 1968 Average plant height2 7/1 7/8 7/15 7/22 In. In. In. In. 22.0 27.2 31.8 37.4 1--------------------------------------2--------------------------------------21.4 25.0 30.0 36.8 3--------------------------------------21.0 26.4 32.8 38.6 30.8 37.2 4-------------------------------------20.4 27.0 20.8 25.6 30.6 37.8 5--------------------------------------6--------------------------------------- 21.6 25.8 30.2 35.6 33.0 38.8 7-----------_--------------------23.0 28.6 --- 7/29 In. 42.4 8/7 In. 46.2 43.2 46.4 48.6 50.4 44.0 44.2 41.4 43.6 48.6 48.8 45.6 47.8 See Table 1 for description of treatments. 2 Averages based on measurement of 25 plants per treatment. 1 plants in these two treatments did not mature. Whereas the check and plots subjected to complete square removal for 1 to 4 weeks showed no significant differences in yield, the yields from the plots subjected to 5 and 6 weeks of square loss were significantly lower. 1968 During the early part of the 1968 test (until July 15), plants in the check plots were taller than plants in any of the plots where plants were deflorated, Table 5. By late July, however, plants in most of the treatments subjected to square loss had become taller than plants in the check. By August 7, the last day of plant measurement, two square removal treatments, 1 and 6, had plants shorter than the check. It was difficult to explain why plants subjected to 6 weeks of square loss were shorter than plants in the check. In 1967, plant measurements made on August 1 showed a similar situation; however, by late August plants in Treatment 6 were considerably taller than plants in the check, Table 2. Counts of the various cotton plant fruiting structures were not made in 1968. However, periodic observations of the test plots showed the check plots to be the first treatment to have open boils (August 10). In Treatment 1, open bolls were first observed on August 17, 56 days after squares were removed from the plants in those plots. Treatment 2, where squares had been removed for 2 successive weeks, had open boils on August 23. On this date, the check plots had an average of 145,600 bolls 8 TABLE ALABAMA AGRICULTURAL EXPERIMENT STATION 6. YIELD OF SEED COTTON FROM SQUARE REMOVAL MARVYN, ALABAMA, 1968 TEST, Treatment' 1 Yield per acre replicatedM 4 3 2 Lb. 1,326 1,014 1-----------------------------------------------------------2- Lb. 1,017 982 Lb. 1,131 Lb. 1,213 Lb. 1,171 ab 3---------------------------------------- 1,037 471 ------------------------4--5 --------------------------------------- 455 6- 668 467 476 430 950 845 692 514 407 1,699 1,017 935 751 601 542 1,185 991 be 871 c d 595 d 511 441 1,826 a ------_------------------- 385 d 1,257 7__---------------------2 1,187 1 See Table 1 for description of treatments. Hand harvested 12/11/68. ' Means followed by same letter are not significantly different at the 5 % level. per acre, 65 per cent of which were open. Plants subjected to 5 and 6 weeks of square removal (Treatments 5 and 6) were still blooming vigorously on August 23. Open bolls were observed in Treatment 3 on August 23 and in Treatments 4 and 5 on September 10. By this time (September 10), 100 per cent of the boils in the check plots were cracked or open; 80 per cent of the bolls in Treatment 1 were cracked or open; and 70 per cent of the boils in Treatment 2 were cracked or open. Yield data for the 1968 test, Table 6 again reflected the influence of early season square loss. However, unlike 1967, plots subjected to 2 or more weeks of square loss produced significantly less cotton than the check plots. Perhaps the relatively little rainfall at the test site in 1968, Table 7, inhibited the cotton plants demonstrated capacity to replace lost squares. 1969 Plant height data, Table 8, followed the pattern observed in 1967 and 1968. Early measurements, made prior to mid-July, TABLE 7. MONTHLY RAINFALL RECORDED AT THE SITE OF THE SQUARE REMOVAL SITE, MARVYN, ALABAMA YerJune In. JulyMot In. 9.01 8.37 Aug. In. 4.13 Sept. In. 8.70 2.05 7.00 1967-----------------1968-------_--2.90 1969 1.60 3.02 3.87 1.70 4.39 INFLUENCE OF EARLY-SEASON INSECT DAMAGE TABLE 8. HEIGHT OF COTTON PLANTS SUBSEQUENT TO EARLY SEASON Loss, MARVYN, ALABAMA, 1969 9 Treatment' 7/1 7/8 Average plant height' 7/15 7/22 7/29 In. 1--------------------------------------24.2 In. 25.2 In. 28.2 In. 29.0 In. 29.1 2--------------------------3----------------------------4----------------------------- ------------------------------ 24.6 24.4 26.4 23.6 25.2 24.8 27.6 25.5 29.3 27.6 29.7 27.0 30.4 28.4 30.3 28.3 30.8 29.2 30.4 28.5 8/5 In. 29.0 30.4 29.2 31.2 28.1 5--------------------------------------24.2 25.6 27.0 27.7 6.---------------------------------------- 28.8 7--------------------------------------1 28.8 24.4 26.0 27.4 28.0 27.8 27.8 See Table 1 for description of treatments. 'Averages based on measurement of 25 plants per treatment. showed plants in the check were taller or as tall as plants in plots subjected to square loss. However, by the first week in August, plants that had lost early season squares had become taller than plants in the check plots. Plants in all treatments fruited much more in 1969 than in the 2 previous years. Counts made 11 weeks after the first date of square removal, Table 9, showed that plants in all plots except Treatment 4 had considerably more than 200,000 fruiting structures per acre. Plants in the check plots (Treatment 7) had fewer total fruiting structures than several square removal treatments; however, all of the fruit in the check plots were bolls, 29 per cent of which were already cracked or open. Over one-third of the fruit in Treatment 6 (plants subjected to 6 successive weeks of square loss) were squares. TABLE 9. NUMBER OF FRUITING STRUCTURES PRESENT 11 WEEKS AFTER FIRST DATE OF SQUARE REMOVAL, MARYYN, ALABAMA, 1969 Treatment' Av. sq/acre No. 0 Av. bolls /acre' Av. cracked or open bolls/acre No. 20,800 No. 197,600 1----- ------------- -2---------------------------. 3------------4---------------------. 5 ---------------------6---------------------. 7-------------------- 7,800 0 0 28,600 130,000 0 377,000 278,200 197,600 223,600 226,200 195,000 row feet on 0 0 0 0 0 78,000 ' Data based on counts of fruiting See Table 1 for description of treatments. structures/lO 9/8/69. 'Blooms were counted as boils. 10 10 ALABAMA AGRICULTURAL TABLE 10. EXPERIMENT STATION YIELD OF SEED COTTON FROM SQUARE REMOVAL TEST, MARVYN, ALABAMA, 1969 Treatment' 1 Yield per acre replicated 2 3 4 2 Mean' 5 Lb. Lb. Lb. Lb. 3,783 4,264 4,186 Lb. 3,627 3,172 3,757 Lb. 3,871 a 3,621 a 3,697 ab 3,770 4,407 3,770 1--------------------------------2--------------------------------3,029 4,420 3,224 3,653 3,328 3--------------------------------3,562 3,380 3,185 3,068 4._______________________________. 2,652 3,458 2,470 5--------------------------------2,197 1,872 2,522 6--------------------------------3,965 3,809 7--------------------------------3,536 3,055 2,639 2,743 3,016 2,691 2,678 2,184 3,075 bc 2,779 2,303 3,642 a cd d 3,887 1 See Table 1 for description of treatments. 'Hand harvested on 10/17 and 11/14. Data includes total for both harvests. 'Means followed by same letter are not significantly different at the 5%olevel. Yields in all treatments were much higher in 1969 than the 2 previous years, Table 10. Total early season square loss for up to 3 successive weeks did not result in any reduction in seed cotton yield. General Discussion The results of this experiment may well give cause for some reassessment of the importance of certain early-season insect festations. Obviously, the cotton plants have the capacity to replace all of the squares lost to early-season attack from such insects as plant bugs and boll weevil. However, the indication that some early-season loss of squares to insect injury might in- even be beneficial must be considered with caution. Adverse climatic conditions during the period following the loss of earlyseason squares could seriously inhibit capacity of cotton plants to compensate for the square loss. Also, in the event of an early onset of cold weather in the fall, a delay in the boll maturity, caused by the loss of early-season squares, might have a disastrous effect on yields. One must also consider the impact of providing an abundance of late season squares and developing bolls as food for the diapausing generation of the boll weevil and bollworm, Heliothis spp., during September and October. These considerations, however, should' not obscure the important point that can be made from the results of this experiment. That is, heavy infestations of square-feeding insects during the early part of the season (prior to the third week of squaring) should not necessarily be of great immediate concern. INFLUENCE OF EARLY-SEASON INSECT DAMAGE 11 LITERATURE CITED H. B., AND J. 0. WARE. 1958. Cotton. 3rd ed., 566 pp. McGraw-Hill. New York. (2) DUNNAM, B. W., J. C. CLARK, AND S. L. CALHOUN. 1943. Effect of the Removal of Squares on Yield of Upland Cotton. J. Econ. Entomol. 36: 896-900. (3) EATON, FRANK M. 1931. Early Defloration as a Method of Increasing Cotton Yields, and the Relation of Fruitfulness to Fiber and Boll Char- (1) BROWN, (4) HAMNER, acters. Jour. Agr. Res. 42(8): 447-62. A. L. 1941. Fruiting of Cotton in Relation to Cotton Fleahopper and Other Insects Which Do Similar Damage to Squares. Miss. Agr. Exp. Sta. Bull. 360: 1-11. (5) TnARP, W. H. 1960. The Cotton Plant. USDA Agr. Handbook No. 178: 1-17. OF ALABAMA'S LAND-GRANT UNIVERSITY With an agricultural research unit in every major soil area, Auburn University serves the needs of field crop, livestock, forestry, and horticultural producers in each region in Alabama. Every citizen of the Stae has a stake in this research program. since any advantage from new and more economical ways of prodiucing and handling farm products directly benefits the consumingi public. i 0 0 03 F 0 Research Unit Identification 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Voiley Substation, belie Mina Sand Mountain Substation, Crossville. North Alabama Horticulture Substation, Cullmar. Upper Coastal Plain Substation, Winfield. Forestry Unit, Fayette County. Thorsby Foundation Seed Stocks Farm, Thorsby Chilton Area Horticulture Substation, Clanton. Forestry Unit, Coosa County. Piedmont Substation, Camp Hill. Plant Breeding Unit, Tallassee Forestry Unit, Autauga County. Prattville Experiment Field, Prattville Black Belt Substation, Marion Junction Tuskegee Experiment Field, Tuskegee. 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 Tennessee