Bulletin 608 December 1990 Alabama Agricultural Experiment Station Lowell T. Frobish, Director Auburn University Auburn University, Alabama I- ~ t tk-s.. A'~~s IF" ~rl) we .- , " s . rwl 't- -.. CONTENTS Page INTRODUCTION.................................... MATERIALS AND METHODS............................................. .................... 3 4 RESULTS AND DISCUSSION............................................. 7 General Comments ............................................ Experiments at the Tennessee Valley Substation.................. Weed Control................................................ Crop Yields.................................................. Experiments at the Wiregrass Substation........................ Weed Control............................................... Crop Yields ................................................. SUMMARY AND CONCLUSIONS ........................................ LITERATURE CITED ................................................... 11 7 7 7 9 11 14 17 19 FIRST PRINTING 4M, DECEMBER 1990 Informationcontainedherein is availableto all persons without regardto race, color, sex, or national origin. Trade Name Common Name Treflan® Trifluralin ................................................................. Prowl® Pendimenthalin ............................................................. Metolachior..................................................................Dual® Atrazine...................................................................Aatrex® Poast® Sethoxydim ................................................................. Cyanazine..................................................................Bladex® Zorial® Norfiurazan ................................................................ Cotoran® Fluometuron ............................................................. Sencor® Metribuzin ................................................................ Blazer® Aciflurofen ................................................................ Bentazon ................................................................ Basagran® Bueno 6® M SMA .................................................................. Common and trade names of herbicides. Weed Control in Minimum Tillage Cotton Rotations MICHAEL G. PATTERSON, WILLIAM B. WEBSTER, HENRY IVEY, AND LARRY W. WELLS' INTRODUCTION servation tillage, has not been universally adopted by cotton (Gossypium hirsutum) farmers in Alabama or other Southeastern States (5). One reason for the reluctance to grow cotton in these tillage systems is the real or perceived problems associated with weed control. Primary and secondary tillage plus herbicide applications provide the basis for weed control in conventional tillage systems, and cotton growers have confidence in this system. Primary tillage and cultivation are generally reduced or eliminated in minimum tillage systems, and weed control is dependent on preplant foliar and broadcast herbicide applications. Several weed species cause economic losses in cotton (7). Annual grasses such as large crabgrass (Digitaria sanguinalis),broadleafweeds including several species of morningglory (Ipomoea spp.), and perennial weeds like johnsongrass (Sorghum halepense) and nutsedge (Cyperus spp.) infest cotton fields. Annual grasses are controlled in conventional tillage cotton primarily by using preplant incorporated treatments of trifluralin and pendimenthalin. 2 Herbicide incorporation is usually eliminated or reduced in minimum tillage systems, thus decreasing the activity of these herbicides. Postemergence herbicides are available for grass control in cotton, but these treatments are generally more expensive than preplant incorporated treatments. Broadleaf weed control in cotton is accomplished with preemergence herbicide applications and postemergence directed sprays in both conventional and minimum tillage systems. These treatments are generally applied to a band centered on the cotton row in conventional 'Respectively, Assistant Professor of Agronomy and Soils, Superintendent of the Tennessee Valley Substation, Belle Mina; Superintendent and Associate Superintendent of the Wiregrass Substation, Headland. 2 Common and some trade names of all the chemicals mentioned in this study can be found on page 2. MINIMUM TILLAGE, also known as reduced, limited, or con- 4 ALABAMA AGRICULTURAL EXPERIMENT STATION tillage systems. Since cultivation is often eliminated in minimum tillage, all preemergence and directed treatments are normally broadcast from row to row. This increases herbicide expense accordingly. However, some of this increase in herbicide expense is offset by a reduction in primary tillage. The benefits of crop rotation are well documented for conventional tillage cropping (2,3,4,6). Currently, rotating crops also implies the rotation of herbicides (8). Certain weeds which may be impossible to control in one crop can be easily controlled in another. Although much information is available for conventional tillage rotations, little is known about the long-term effects of weed control and crop yields in minimum tillage cotton rotations. The objectives of the studies reported herein were to evaluate weed control and crop yields from minimum (strip) tillage cotton grown in rotation as well as continuously cropped, and compare these data to the results from the same rotations under conventional tillage. MATERIALS AND METHODS Field experiments were conducted for 4 years (1985-88) at the Tennessee Valley Substation, Belle Mina, and the Wiregrass Substation, Headland. Cotton was grown continuously or in rotation, using strip tillage and conventional tillage. Rotational sequences are listed in table 1. TABLE 1. ROTATIONAL SEQUENCES FOR EXPERIMENTS AT BELLE MINA AND HEADLAND' Location 1985 Belle Mina 1986 corn soybeans cotton cotton peanuts sorghum cotton cotton peanuts Crop 1987 soybeans cotton corn cotton sorghum cotton peanuts cotton peanuts 1988 cotton corn soybeans cotton cotton peanuts sorghum cotton peanuts cotton corn soybeans cotton .......................... Headland ........................... cotton peanuts sorghum cotton peanuts 'All crop rotations were grown in strip and conventional tillage. Crops were grown on 30-foot-long plots which were 12 rows (40 or 36 inches) wide for cotton and peanuts and 16 rows (30 inches) wide for corn, soybeans, and grain sorghum. Four replications of each treatment were used in a randomized complete block design. Crops were planted WEED CONTROL IN MINIMUM TILLAGE COTTON 5 during the period from April 15 to May 25 each year. Land preparation for conventionally tilled plots included moldboard plowing, disking twice, and leveling with a field cultivator. Preplant incorporated herbicides were incorporated with the field cultivator for cotton and soybeans and with the second disking for peanuts. Strip tillage plots were planted to wheat in the fall preceding each growing season. Paraquat at 0.5 pound a.i. (active ingredient) per acre was used to kill the wheat cover crop in March prior to planting. Plots were prepared 2 weeks before planting using a Ro-Till3 machine which provided a tilled strip approximately 18 inches wide over the row. Crops were planted in these strips after rainfall had settled the tilled soil using Max-emerge 4 planters. Pendimethalin was used as a preemergence herbicide in strip-tillage cotton, soybean, and peanut plots and applied just before the Ro-Till operation. Pendimethalin was used as the preplant incorporated herbicide in conventional tillage cotton, soybeans, and peanuts. The herbicide programs used for each crop are listed in table 2. Crop varieties were selected based on yields from Alabama Agricultural Experiment Station variety trials. At the Tennessee Valley Substation, Deltapine 50 cotton, Essex soybeans, and Pioneer brand 3320 corn were planted. At the Wiregrass Substation, Deltapine 90 cotton, Florunner peanuts, and Funk's 522 DR sorghum were planted. Predominant weed species at the Tennessee Valley Substation were annual grasses [large crabgrass and fall panicum (Panicum dichotomiflorum)], annual morningglories [pitted (I. lacunosa) and entireleaf (I. hederacea)],and prickly sida (Sida spinosa).Predominant species at the Wiregrass Substation were annual grasses [Texas panicum (Panicum texanum) and large crabgrass], sicklepod (Cassia obtusifolia), annual morningglories [pitted and smallflower (Jacauemontia tamnifolia)], and Florida beggarweed (Desmodium tortuosum). All production inputs, including soil fertilization, liming, and disease and insect control, were maintained for optimum crop production. An N-P starter fertilizer solution (20-20-0) was used with strip tillage cotton plots at the Wiregrass Substation, which appeared to provide good growoff of seedling plants. Weed control ratings were obtained in August each year after all herbicide treatments had been applied. Crop yields were obtained at harvest and are reported on a per acre basis. 3 Bush-Hog 4 Corp., Selma, Alabama. John Deere Tractor Co., East Moline, Illinois. 6 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 2. HERBICIDE PROGRAMS USED FOR CROPS GROWN CONTINUOUSLY OR IN ROTATION AT BELLE MINA AND HEADLAND' Crop Cotton Tillage conventional Herbicide 1\ I ; Rate, lb. a.i./acre 0.5 2.0 0.5 2.0 0.5 1.0 2.0 0.5 2.0 0.5 0.38 0.38 0.5 1.0 0.38 0.38 1.0 2.0 0.125 0.5 0.5 1.0 2.0 0.125 2.0 2.0 0.5 2.0 2.0 2.0 2.0 0.5 2.0 2.0 0.25 Application method preplant incorporated preemergence, band postemergence, directed postemergence, directed preplant foliar preemergence preemergence postemergence, directed postemergence, directed preplant incorporated preemergence, band postemergence preplant foliar preemergence postemergence postemergence prelant incorporated preemergence postemergence postemergence preplant foliar preemergence preemergence postemergence preemergence preemergence preplant foliar preemergence preemergence preemergence postemergence preplant foliar preemergence postemergence postemergence, directed Pendimethalin Fluometuron Cyanazine MSMA Paraquat Pendimethalin Fluometuron Cyanazine MSMA Pendimethalin Metribuzin Aciflurofen Paraquat Pendimethalin Metribuzin Aciflurofen Pendimethalin Metolachlor Paraquat Bentazon Paraquat Pendimethalin Metolachlor Paraquat Metolachlor Atrazine Paraquat Metolachlor Atrazine Metolachlor Atrazine Paraquat Metolachlor Atrazine Paraquat Cotton strip Soybeans conventional Soybeans strip Peanuts conventional Peanuts 2 strip Corn Corn conventional strip Sorghum Sorghum conventional strip 'All conventional tillage plots were cultivated twice during the growing season. Postemergence applications of sethoxydim (0.28 lb. a.i./acre) were used to supplement annual grass control in continuous peanut plots during 1987 and 1988. 2 WEED CONTROL IN MINIMUM TILLAGE COTTON 7 RESULTS AND DISCUSSION General Comments Good cotton stands were obtained in strip tillage plots at both locations. The Ro-Till machine used on the clay loam soil at the Tennessee Valley Substation was equipped with modified subsoil shanks set for a depth of 6 to 8 inches. Standard shanks which run to a depth of 12 to 14 inches resulted in excessive amounts of subsoil clay being pulled to the surface. Standard subsoil shanks were used on the sandy loam soil at the Wiregrass Substation and worked well. Good corn stands were obtained with the strip tillage system at the Tennessee Valley Substation. Soybean stands in strip-tilled plots were lower than soybean stands in conventional till plots at that location. This may have been attributable to seedbed preparation associated with the Ro-Till machine. Conventional tillage provided a better seedbed, which resulted in more uniform placement of soybean seed. Good stands of cotton and peanuts were obtained with strip tillage planting at the Wiregrass Substation in all years. A poor grain sorghum stand in 1985 resulted in large skips and therefore unacceptable weed control and crop failure in both tillage systems. Experiments at the Tennessee Valley Substation Weed Control Annual grass control in both strip and conventional tillage cotton grown continuously over the 4-year study was greater than 90 percent, table 3. The combination of preemergence herbicides and postemergence directed sprays was effective in both tillage systems. Good pre- TABLE 3. WEED CONTROL IN CONTINUOUS COTrON GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT BELLE MINA' Weed species 2 Tillage 1985 Pct. Year 1986 Pet. Av. 1987 Pct. 1988 Pct. Pct. Annual grass Morningglory Prickly sida strip cony. strip cony. strip cony. 95 95 95 93 95 88 90 90 88 90 90 90 93 99 99 99 98 99 99 99 99 99 99 99 94 96 95 95 95 94 2Annual grasses = large crabgrass, fall panicum; morningglory = pitted and entireleaf. 'Tillage treatments were maintained on the same plots each year. 8 ALABAMA AGRICULTURAL EXPERIMENT STATION emergence herbicide activation each year and timely directed sprays provided weed control until the crop canopy closed. Pitted morningglory and prickly sida control in continuous cotton was excellent overall in both tillage systems. Annual grass, morningglory, and prickly sida control in rotational cotton was good to excellent during the 4-year period, table 4. Except for paraquat used to kill the wheat cover each spring, identical weed control programs were used in both continuous and rotational cotton grown under both tillage systems. This indicates that good weed control can be obtained in strip-tillage cotton with herbicides currently used in conventional systems. However, because herbicides were broadcast in strip-tillage plots, the cost of chemicals used in this system was approximately 200 percent greater than in conventional-tillage cotton. TABLE 4. WEED CONTROL IN ROTATIONAL COTTON GROWN WITH MINIMUM AND CONVENTIONAL TILLAGE AT BELLE MINA' Weed species 2 Tillage 1985 Pet. Year 1986 Pct. 1987 Pct. 1988 Pct. Av. Pct. Annual grass Morningglory Prickly sida strip cony. strip con. strip con. 95 95 95 95 90 84 90 90 83 90 90 90 93 99 99 99 98 99 99 99 99 99 99 99 94 96 94 96 94 93 'Rotation sequence: cotton - corn - soybeans - cotton. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Annual grasses = large crabgrass, fall panicum; morningglory = pitted and entireleaf. Weed control in rotational corn was good under both tillage systems, table 5. Metolachlor and atrazine were used for weed control in both tillage systems. No herbicide carryover from atrazine to rotational soybeans was observed. Herbicide cost for corn in strip tillage was only slightly higher than conventional tillage since atrazine is normally broadcast in both systems. Banding metolachlor in conventional tillage can reduce the cost; however, the cultivations used in conventional tillage add some additional weed control costs to this system. Weed control in rotational soybeans was good to excellent in conventional-tillage plots during all 4 years, table 6. Annual grass control in 1986, morningglory control in 1985 and 1986, and prickly sida control in 1985 were poor in strip-tillage plots. This can be explained in part by the poor soybean stand obtained using strip tillage in these years. WEED CONTROL IN MINIMUM TILLAGE COTTON 9 Drought conditions in 1988 prevented many weed seed from germinating, resulting in excellent weed control. No herbicide carryover to rotational cotton was observed during any year. TABLE 5. WEED CONTROL IN ROTATIONAL CORN GROWN WITH MINIMUM AND CONVENTIONAL TILLAGE AT BELLE MINA' Weed species" Tillage 1985 1986 Pct. 90 90 90 90 90 90 Pct. 95 93 81 78 79 80 Year 1987 Pct. 92 99 96 99 98 99 1988 Pct. 99 99 99 99 99 99 Av. Pct. 94 95 91 91 91 92 Annual grass Morningglory Prickly sida strip conyv. strip cony. strip conyv. 'Rotation sequence: corn - soybeans - cotton - corn. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Annual grasses = large crabgrass, fall panicum; morningglory = pitted and entireleaf. TABLE 6. WEED CONTROL IN ROTATIONAL SOYBEANS GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT BELLE MINA l Weed species 2 Tillage Year 1985 Pet. 93 89 60 843 69 843 1986 Pct. 58 903 68 903 78 88 1987 Pct. 89 99 99 95 99 99 1988 Pct. 95 95 95 95 95 95 Av. Pct. 84 93 80 91 85 91 Annual grass Morningglory Prickly sida strip conv. strip cony. strip cony. 'Rotation sequence: soybeans - cotton - corn - soybeans. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Annual grasses = large crabgrass, fall panicum; morningglory = pitted and entireleaf. 3Significant difference between tillage treatments at the 5% level. Crop Yields Seed cotton yields from strip and conventional-tillage continuous cotton were approximately equal over the 4-year period, table 7. However, a trend toward reduced yields with strip tillage, although not significant, was evident. Cotton yields from rotational plots followed a similar pattern, but significant decreases were observed in strip tillage plots in 1987 and 1988. Cotton maturity in strip tillage plots was approximately 2 weeks behind conventional tillage cotton in all years. This can 10 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 7. SEED COTTON YIELDS FROM CONTINUOUS AND ROTATIONAL COTTON GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT BELLE MINA' Tillage Yield/year/acre 1985 Lb. 1986 1987 1988 Lb. 1,265 1,483 1,177 1,6522 Av Lb. 1,876 1,995 1,792 2,110 Strip .......................... Conventional ................. Strip .......................... Conventional ............... 3,019 3,003 2,910 3,076 Lb. Lb. Continuous 1,416 1,804 1,868 1,624 Rotational 1,804 1,277 1,6672 2,046 'Rotation sequence: cotton - corn - soybeans - cotton. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Significant difference between tillage treatments at the 5% level. be viewed as a detriment to strip tillage at the north Alabama location where the growing season is relatively short. Corn and soybean yields from rotational plots varied greatly over the 4-year period, table 8. Strip-tillage yields were significantly lower overall than conventional-tillage yields. Drought conditions affected corn yields in 1988 and soybean yields in 1987. During these years, strip-tillage yields were equal to or better than conventional-tillage yields. Part of the yield reduction in strip-tillage soybeans can be attributed to poor stand and the resultant poor weed control in these plots discussed earlier. TABLE 8. CORN AND SOYBEAN YIELDS FROM ROTATIONAL PLOTS GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT BELLE MINA' Tillage 1985 Bu. Yield/year/acre 1986 1987 Bu. Corn 54 1222 Soybeans 28 452 1988 Bu. 272 7 28 422 Av. Bu. 63 83 25 38 Bu. 92 117 18 15 Strip .......................... Conventional ................ Strip .......................... Conventional ................. 81 85 28 502 'Rotation sequence: corn - soybeans - cotton - corn. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Significant difference between tillage treatments at the 5% level. WEED CONTROL IN MINIMUM TILLAGE COTTON 11 Experiments at the Wiregrass Substation Weed Control Annual grass control in strip tillage continuous cotton was good to excellent in 1985 and 1986, table 9. However, control in 1987 and 1988 was poorer and can be attributed in part to the presence of Texas panicum in these plots. Texas panicum is a large seeded annual grass which is difficult to control even in conventional tillage systems where good herbicide incorporation can be obtained. Pendimethalin activity is significantly reduced on Texas panicum when this herbicide is used preemergence as was done in strip tillage. Conventional tillage grass control was only slightly better overall. Annual morningglory, sicklepod, and Florida beggarweed control was good to excellent each year in both strip and conventional-tillage continuous cotton. TABLE 9. WEED CONTROL IN CONTINUOUS COTTON GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT HEADLAND' Weed species2 Year Tillage 1985 Pct. 1986 Pct. 1987 Pct. 1988 Pct. Av. Pct. Annual grass Morningglory strip cony. strip 93 95 93 83 80 93 75 69 95 73 893 89 81 83 93 Sicklepod Florida beggarweed cony. strip cony. strip cony. 94 93 91 94 95 93 94 94 95 95 92 963 80 98 95 87 97 97 99 99 92 95 91 97 96 'Tillage treatments were maintained on the same plots each year. 2Annual grasses = large crabgrass, Texas panicum; morningglory = pitted and smallflower. 3Significant difference between tillage treatments at the 5% level. Annual grass control in continuous strip-tillage peanuts was good initially in 1985, but declined over the next 3 years, table 10. Although supplemental postemergence applications of sethoxydim were used in 1987 and 1988, grass control was less than ideal. Except for annual morningglory (primarily smallflower) and Florida beggarweed control in 1988, overall broadleaf weed control was good and approximately equal for both tillage systems. Weed control in rotational cotton was equal in both tillage systems over the 4-year period except for annual grass control in 1988, table 11. Annual morningglory control was good to excellent in all years. Sicklepod control equal to or greater than 90 percent was obtained each year 12 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 10. WEED CONTROL IN CONTINUOUS PEANUTS GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT HEADLAND' Weed species2 Tillage Year 1985 Pct. 91 95 93 95 90 89 76 86 1986 Pct. 76 74 82 84 71 75 78 81 1987 Pct. 83 94 88 93 95 91 953 83 1988 Pct. 69 983 53 873 75 82 63 913 Av. Pct. 80 90 79 90 83 84 78 85 Annual grass Morningglory Sicklepod Florida beggarweed strip cony. strip cony. strip cony. strip cony. 'Tillage treatments were maintained on the same plots each year. 2Annual grasses = large crabgrass, Texas panicum; morningglory = pitted and smallflower. 3Significant difference between tillage treatments at the 5% level. TABLE 11. WEED CONTROL IN ROTATIONAL COTTON GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT HEADLAND' Weed species2 Tillage Year 1985 Pct. 92 95 89 95 93 90 95 95 1986 Pct. 68 71 90 89 77 83 94 95 1987 Pct. 78 72 96 95 96 92 99 94 1988 Pct. 77 933 84 92 96 97 98 99 Av. Pct. 79 83 90 93 91 91 97 96 Annual grass Morningglory Sicklepod Florida beggarweed strip cony. strip cony. strip cony. strip cony. 'Rotation sequence: cotton - peanuts - grain sorghum - cotton. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Annual grasses = large crabgrass, Texas panicum; morningglory = pitted and smallflower. 3Significant difference between tillage treatments at the 5% level. except 1986. Postemergence-directed sprays with cyanazine plus MSMA reduced Florida beggarweed populations for rotational peanuts following cotton. Although not used in this rotation, norflurazon could be included with fluometuron if additional broadleaf weed control was needed, without detrimental effects to the following peanut crop. Both annual grass and broadleaf weed control was better in conventional-tillage rotational peanuts than in strip tillage, table 12. Cultivation was especially beneficial for annual grass and annual morningglory WEED CONTROL IN MINIMUM TILLAGE COTTON TABLE 12. WEED CONTROL IN ROTATIONAL PEANUTS GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT HEADLAND' 13 Year Weed species' Tillage 1985 Pct. 1986 Pct. 1987 Pct. 1988 Pct. Av. Pct. Annual grass Morningglory Sicklepod Florida beggarweed strip cony. strip cony. strip cony. strip cony. 85 953 92 95 86 933 64 71 72 68 77 903 72 77 86 87 73 923 76 903 88 93 85 943 80 973 84 87 91 90 94 98 77 88 82 91 84 88 78 85 'Rotation sequence: - peanuts - grain sorghum - cotton - peanuts. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Annual grasses = large crabgrass, Texas panicum; morningglory = pitted and smallflower. 'Significant difference between tillage treatments at the 5% level. control. Except for sicklepod control in 1985 and Florida beggarweed control in 1987, control levels were equal for these species in both tillage systems. Paraquat applied over the top generally provided good contact kill of small weeds. However, paraquat is weak on crabgrass and smallflower morningglory and these species were present at harvest. Herbicide costs for strip tillage peanuts would compare favorably with conventional tillage since broadcast applications are normally applied in conventional systems. However, poor grass control from preemergence pendimethalin applications necessitated supplemental postemergence applications of sethoxydim, which significantly increased herbicide cost. A poor grain sorghum stand in 1985 resulted in less than ideal weed control from both tillage systems, table 13. Good stands in following years resulted in better weed control in both tillage systems. Except for annual grass control in 1987, weed control was equal in both tillage systems from 1986 to 1988. Postemergence over-the-top application of atrazine and postemergence-directed sprays of paraquat in strip tillage or cultivation in conventional systems provided season long control. A narrow row spacing (30 inches) combined with the competitive nature of grain sorghum aided weed control. Weed control costs for grain sorghum in both tillage systems are approximately equal since atrazine is normally broadcast in conventional tillage and the post-directed paraquat application compares favorably with cultivation. 14 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 13. WEED CONTROL IN ROTATIONAL GRAIN SORGHUM GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT HEADLAND' Weed species 2 Tillage 1985 1986 Pct. 91 95 95 95 95 95 95 95 Pet. 69 793 48 813 65 853 30 563 Year 1987 Pct. 51 693 89 88 62 58 92 89 1988 Pct. 88 94 89 95 93 87 94 98 Av. Pct. 75 84 80 90 79 81 78 85 Annual grass Morningglory Sicklepod Florida beggarweed strip conv. strip conv. strip conv. strip conv. 'Rotation sequence: grain sorghum - cotton - peanuts - grain sorghum. Each crop was established on separate plots in 1985 to start the rotation. Tillage plots were maintained on the same plots each year. 2 Annual grasses = large crabgrass, Texas panicum; morningglory = pitted and smallflower. 3Significant difference between tillage treatments at the 5% level. Crop Yields Seed cotton yields from strip and conventional-tillage continuous cotton were equal overall for the 4-year period at the Wiregrass Substation, table 14. Strip tillage outyielded conventional-tillage in 1987, and the reverse was true in 1988. Strip-tillage peanut yields were lower than conventional-tillage yields with continuous cropping in 1986 and 1988, and a trend toward reduced yield was apparent in 1987. Part of this decrease can be explained as a result of poor weed control in strip tillage plots during 1988. However, disease increases also figured into continuous strip-tillage peanut yield reductions (discussed later). TABLE 14. YIELDS FROM CONTINUOUS COTTON AND PEANUTS GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT HEADLAND' Tillage 1985 Lb. Strip .......................... Conventional ................. Strip .......................... Conventional ................. 3,443 3,201 2,481 2,659 Yield/year/acre 1986 Lb. 3,654 4,011 1,289 1,9362 1987 Lb. 2,1172 1,639 1,787 2,123 1988 Lb. 2,348 2,6382 1,519 2,3052 Av. Lb. 2,890 2,872 1,769 2,256 Seed cotton Peanuts 'Tillage treatments were maintained on the same plots each year. 2Significant difference between tillage treatments at the 5% level. WEED CONTROL IN MINIMUM TILLAGE COTTON 15 Average seed cotton yields in rotation were approximately equal for both tillage systems over the 4-year period, table 15. Higher yields were obtained from conventional-tillage plots in 1986 and 1987, while striptillage produced more cotton in 1988. Strip-tillage peanut yields in rotation were approximately equal to conventional-tillage yields overall during the 4-year period, table 15. Conventional tillage did outyield strip-tillage peanuts in 1987. Rotation TABLE 15. COTTON, PEANUT, AND GRAIN SORGHUM YIELDS FROM ROTATIONAL PLOTS GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT HEADLAND' Tillage 1985 Lb. Strip .......................... 3,618 Yield/year/acre 1986 Lb. 2,438 1987 Lb. 2,020 1988 Lb. 2,6142 Av. Seed cotton Lb. 2,672 Conventional ................. 3,467 Lb. 2,580 2,641 3,237' Lb. 2,348 2,263 Bu. 2,438' Lb. 2,205 2,9702 Bu. 2,263 Lb. 2,916 2,765 Bu. 2,851 Lb. 2,512 2,652 Bu. Peanuts Strip .......................... Conventional ................. Grain sorghum Strip .......................... Conventional ................. ---- 42' 36 25 21 116' 97 61 51 'Rotation sequence: cotton - peanuts -grain sorghum -cotton. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 'Significant difference between tillage treatments at the 5% level. provided greater overall peanut yields than continuous cropping in both strip (2,512 vs. 1,759 pounds per acre) and conventional (2,652 vs. 2,256 pounds per acre) tillage, respectively, tables 14 and 15. The advantages of rotation in strip tillage appears greater for peanuts than for cotton. Grain sorghum yields were higher in strip than conventional tillage in 1986 and 1988. Yields were not obtained in 1985 due to a poor stand. Volunteer peanuts are a problem in conventional-tillage culture, especially where peanuts are not rotated with other crops. Visual ratings of volunteer peanut control were obtained in continuous and rotational peanuts grown under both tillage systems, table 16. Good to excellent volunteer peanut control was obtained in both strip- and conventionaltillage rotational peanuts. Poor volunteer peanut control was obtained in strip-tillage continuous peanuts. Atrazine used in grain sorghum fol- lowing peanuts in rotation effectively controlled volunteer peanuts in both tillage systems. 16 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 16. VOLUNTEER PEANUT CONTROL IN CONTINUOUS AND ROTATIONAL PEANUTS GROWN WITH STRIP AND CONVENTIONAL TILLAGE AT HEADLAND Tillage 1986 Pct. Year 1987 Pct. Continuous 41 632 Rotational' 90 95 1988 Pct. 25 902 96 98 Av. Pct. 51 81 91 94 Strip ........................ Conventional ................. Strip ........................ Conventional ................. 86 90 87 90 'Rotation sequence: peanuts - grain sorghum - cotton - peanuts. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Significant difference between tillage treatments at the 5% level. White mold (Sclerotium rolfsii) is a serious disease of peanuts (1). Rotation of peanuts in conventional tillage provides an effective means of reducing the incidence of white mold. Little is known about the effects of rotation in minimum tillage on the incidence of white mold. Ratings obtained in this study show white mold can be significantly reduced by rotation in a strip-tillage cropping system, table 17. The increase of white mold in continuous strip-tillage peanuts is apparent. The buildup of white mold in continuous strip-tillage peanuts would prevent this cropping system from succeeding. However, rotational peanuts could be grown in strip tillage without sacrificing yield, table 15. TABLE 17. INCIDENCE OF WHITE MOLD IN CONTINUOUS ROTATIONAL PEANUTS GROWN WITH STRIP AND CONVENTIONAL TILLAGE Hits/year/acre Tillage Av. 1986 Strip .......................... 2,9652 1987 Continuous 4,7802 1988 8,1682 5,304 Conventional ................ Strip ......................... Conventional ................ 2,178 1,815 1,694 3,509 Rotational' 3,146 2,360 3,872 2,541 3,7512 3,186 2,501 2,602 'Rotation sequence: peanuts - grain sorghum - cotton - peanuts. Each crop was established on separate plots in 1985 to start the rotation. Tillage treatments were maintained on the same plots each year. 2Significant difference between tillage treatments at the 5% level. WEED CONTROL IN MINIMUM TILLAGE COTTON 17 SUMMARY AND CONCLUSIONS Weed control in continuous or rotational cotton grown in long-term strip tillage can be successfully accomplished. However, broadcast herbicide applications required in this tillage system increase chemical costs approximately 200 percent above conventional tillage. Minimumtillage cultivation equipment now available may reduce herbicide costs, but this equipment must be evaluated before recommendations can be made. Cotton can be grown continuously in strip tillage without sacrificing yield. Rotation with corn and soybeans at the Tennessee Valley Substation did not provide any advantage for strip-tillage cotton yields. Corn and soybean yields were lower in strip than conventional tillage at that location. Peanut yields in strip-tillage rotation were equal to conventional-tillage yields. Supplemental postemergence grass herbicide treatments will increase weed control costs in strip tillage peanut production. Continuous strip-tillage peanut yields were adversely affected by the buildup of white mold. 18 ALABAMA AGRICULTURAL EXPERIMENT STATION WEED CONTROL IN MINIMUM TILLAGE COTTON 19 LITERATURE CITED (1) (2) AMERICAN PHYTOPATHOLOGICAL SOCIETY. 1984. Compendium of Peanut Dis- (3) (4) eases. Porter, D.M., D.H. Smith, and R. Rodriguez-Kabana (ed). COPE, J.T., JR., AND D.L. THURLOW. 1980. Corn-Wheat-Soybean Rotations and Their Response to Nitrogen, Phosphorus, Potassium. Ala. Agr. Exp. Sta. Highlights of Agr. Res. 27(3):16. HAUSER, E.W., C.C. DOWLER, M.C. JELLUM, AND S.R. CECIL. 1974. Effects of Herbicide-Crop Rotation on Nutsedge, Annual Grasses, and Crops. Weed Sci. 22:172-176. LEIGHTY, C.E. 1938. Crop Rotation. Pages 406-430. In USDA Yearbook of Agr. Soils and Men. MCWHORTER, G.C. AND T. N. JORDAN. 1985. Limited Tillage Cotton Produc- (5) (6) (7) (8) tion. Pages 61-76. In A. Weise (ed). Weed Control in Limited Tillage Systems. Monograph No. 2. Weed Sci. Soc. Amer. Champaign, Ill. NATIONAL RES. COUNCIL. 1989. Research and Science. Pages 135-194. In Alternative Agriculture. Nat. Res. Council. Nat. Acad. Press, Washington, D.C. PATTERSON, MIKE (chairman). 1988. Report of the Cotton Weed Loss Committee. Pages 392-395. In Proc. Cotton Prod. Res. Conf. National Cotton Council of Amer. Memphis, Tenn. WALKER, ROBERT H. AND GALE A. BUCHANAN. 1982. Crop Manipulation in In- tegrated Weed Management Systems. Weed Sci. Suppl. Vol. 30, pp. 17-34. Alabamia's Agricultural Experiment Station System AUBURN UNIVERSITY \\ith an tt .tgrclc h Ul Iit ki it11 i rect.Itl It -Auhuitn I n t\ trsit\ . fSreilxcthis tvscj)rl it tilg .iiicl hIUCllJro Reeach Ucin i I -''-l~tof zcu Main Sagrltral Exeimn StationAuburn. E.~ V. SitchReeac Cener So tr Mn ' 1 Tennesse Val ey Su tao Bel rll 2 Sandl Mountal Sustto Crsv nl\ 7 Ftry UcntCosa thent B)sI Pienon Subtat on.CapHl lbesrch 1 12 13 14 15 Unit Identification EprattimetSatoeuun Pratn Ag FprimentuFiel Black BeltaiSubstation. arossnciln Nth Alrnbaee HonriutrePlsaUion Sprimns Lower Coastal Plain Substation. Camied Forestry Uit, Barbour County. Forestry o Edu.CosaCton Cete oni prnglil 17 WhiloArega Suniulu onlHeadlan in Sbtat 19So7 20 OrnamentalubHorticulurCsat 14 GLfwe CoastaPi Substation ai mdene