Progress 07/01/01 to 06/30/07
Outputs
OUTPUTS: Studies were conducted to: 1) evaluate the impact of PRE herbicides on April-planted soybean; 2) determine optimum timings for POST glyphosate applications in Roundup Ready soybean planted at various dates; 3) evaluate the impact of postemergence metolachlor, tillage, and row spacing on late-season annual grass infestations in early-maturing soybean; 4) assess the impact of single glyphosate applications, sequential glyphosate applications, and glyphosate tank mixtures on control of different sized pitted morningglory plants; 5) evaluate flame cultivation for weed control in organically grown soybean; and 6) evaluate the impact of postemergence metolachlor, tillage, and row spacing on late-season annual grass infestations in early-maturing soybean. Full rates of Canopy XL and Sencor reduced yield. Reduced rates of PRE broadleaf herbicides alone generally did not reduce yield. PRE broadleaf herbicides mixed with Prowl or Dual often increased injury and sometimes reduced yield. Many treatments did not reduce yield but impeded growth and development, which would likely reduce crop competitiveness with weeds. Weed control was higher with 15-inch row spacings than with 30-inch row spacings. Sequential applications were often necessary with 30-inch rows to achieve weed control similar to single applications in 15-inch rows. Maximum yield was achieved with glyphosate applications made 4 to 6 and 3 to 4 weeks after planting in late-March to April-planted and May-planted soybean, respectively. Annual grass biomass was 31 to 38% lower in plots treated with 0.84 kg/ha glyphosate + 1.8 or 1.3 kg/ha s-metolachlor compared to plots treated with glyphosate alone. Annual grass biomass at harvest was not influenced by tillage, but was 51% less in 38-cm rows compared to 76-cm rows. Glyphosate at 0.94 and 0.75 lb ae/A was required to provide maximum control of vining morningglory plants and 3- to 5-leaf plants, respectively. Control with 0.75 lb ae/A fb 0.56 lb ae/A was generally similar to the best single applications. Tank mixing chlorimuron or cloransulam with 0.56 lb ae/A glyphosate generally did not improve control compared to 0.56 lb ae/A glyphosate alone. Using 0.94 or 1.12 lb ae/A glyphosate as a single application or a sequential application of 0.75 lb ae/A fb 0.56 lb ae/A essentially eliminated seed production. In April-planted studies, flame weed control produced soybean yields of 48 bu/A that were similar to the 50 bu/A that was achieved with two applications of glyphosate. In May plantings, soybean yields with flame cultivation equaled those achieved with the glyphosate-resistant program only 1 of 2 years. Soybeans grown organically using flame weed control would have to be sold for a premium of approximately $2 per bushel to equal returns that would occur using the glyphosate only system. Annual grass biomass was 31 to 70% lower in plots treated with 0.84 kg/ha glyphosate + 1.8 or 1.3 kg/ha s-metolachlor compared to plots treated with glyphosate alone. There was 51 to 63% less grass biomass in 38 cm rows than in 76 cm rows. PARTICIPANTS: No Participant information reported. TARGET AUDIENCES: No Target Audiences information reported. PROJECT MODIFICATIONS: No Project Modifications information reported.
Impacts
Reducing PRE herbicide use and rates in early-planted soybeans or matching tolerant varieties to herbicide programs should improve yield in early-planted soybeans and improve the crop's ability to compete with weeds. Sequential glyphosate applications may not be required for Roundup Ready soybeans planted in narrow rows prior to May 1 some years. Early planting dates will allow producers more time to make POST herbicide applications making it easier to farm larger acreages with less labor and equipment. By narrowing row spacings and/or using post metolachlor applications in early-maturing soybean, producers can reduce late-season grass infestations in early-maturing soybean 30 to 50 percent thereby increasing harvest efficiency and reducing the likelihood of using pre-harvest desiccants. Glyphosate rates of at least 0.94 lb ae/A will provide consistent control of all sizes of pitted morningglory and significantly reduce the number of pitted morningglory seed in the soil seed bank. Flame weed control can be used to profitably produce organically grown soybean thereby creating a specialty market for small producers.
Publications
- Poston, D.H., V.K. Nandula, R.M. Griffin, and C.H. Koger. 2007. Texasweed (Caperonia palustris) control in soybean with postemergence herbicides. Weed Technology 21:670-673.
- Nandula, V. K., D. H. Poston, T. W. Eubank, C. H. Koger, and K. N. Reddy. 2007. Differential response to glyphosate in Italian ryegrass (Lolium multiflorum) populations from Mississippi. Weed Technology 21:477-482.
- Nandula, V. K., K. N. Reddy, A. M. Rimando, S. O. Duke, and D. H. Poston. 2007. Glyphosate resistant and susceptible soybean (Glycine max) and canola (Brassica napus) dose response and metabolism relationships with glyphosate. Journal of Agricultural and Food Chemistry 55:3540-3545.
- Nandula, V. K., D. H. Poston, K. N. Reddy, and C. H. Koger. 2007. Formulation and adjuvant effects on uptake and translocation of 14C-clethodim in bermudagrass (Cynodon dactylon). Weed Sci. 55:6-11.
- Poston, D.H., V. K. Nandula, R. M. Griffin, D. R. Shaw, and M. C. Smith. 2007. Weed control alternatives in very early-maturing Mississippi soybean. Crop Management doi: 10.1094/CM-2007-0323-02-RS.
- Eubank. T. W., D. H. Poston, V. K. Nandula, C. H. Koger, D. R. Shaw , and D. Reynolds. 2007. Glyphosate-resistant horseweed control using glyphosate-, paraquat-, and glufosinate-based herbicide programs. Accepted in Weed Technology.
- Nandula, V. K., D. H. Poston, K. N. Reddy, and C. H. Koger. 2007.Formulation and adjuvant effects on uptake and translocation of 14C-clethodim in wheat (Triticum aestivum L.). Weed Biology and Management 7:226-231.
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Progress 01/01/06 to 12/31/06
Outputs
Averaged across locations, horseweed emerged primarily in the fall of the year, September through early November, when temperatures ranged from 16 to 23 C with subsequent emergence occurring from late January through early April when temperatures ranged from 5 to 16 C. No emergence to very low emergence was observed from late November through early March. Tillage in September followed by (fb) glufosinate in March was included as a comparison treatment because fall tillage fb chemical weed removal in the spring is a common practice in the Mississippi Delta. . Tillage in September fb glufosinate in March provided 100% horseweed control. Horseweed control with glufosinate in March and tillage in March was comparable. Percent horseweed groundcover in May averaged across locations was 0, 4, and 8% for tillage in September fb glufosinate in March, glufosinate in March, and tillage in March, respectively. Horseweed control with tillage in November and glufosinate in November
was comparable to tillage in September fb glufosinate in March at only 1 and 2 of 3 locations, respectively. Tillage in November failed to completely kill emerged horseweed at one location and new emergence following November tillage occurred at all locations. Glyphosate at 0.86 kg ae/ha alone provided 60 to 65% horseweed control 4 WAT. Control 4 WAT ranged from 73 to 74% when the glyphosate rate was increased to 1.25 kg ae/ha. Glyphosate + 2,4-D and glyphosate + dicamba were the best glyphosate-based treatments and provided 90% or better horseweed control 4 WAT both years. Soybean yields with glyphosate + 2,4-D and glyphosate + dicamba were equal to the best treatments both years. Control 4 WAT with paraquat alone ranged from 55 to 63% and control was not improved by increasing the rate from 0.84 to 0.98 kg ai/ha. In 2005 paraquat + metribuzin provided 94% horseweed control 4 WAT and reduced horseweed plant populations 96%. Horseweed control 4 WAT in 2006 with paraquat + 2,4-D and
paraquat + dicamba was 88 and 89%, respectively. Control with these treatments was significantly better than with paraquat + metribuzin, which provided only 79% control in 2006 4 WAT. Glufosinate-based burndowns provided 81 to 97% horseweed control and soybean yields were generally similar with all glufosinate-based programs. Soybean yields were generally best with herbicide programs that provided that highest level of horseweed control. Italian ryegrass with 3-fold tolerance to glyphosate has been identified. Glyphosate completely controlled a known-susceptible population. Control of resistant plants by glyphosate decreased from 80 to 98% for small sized plants to 44 to 79% for larger plants. Diclofop provided 38% control of small plants from one resistant population and was ineffective on large plants from all three populations. Control with mesosulfuron was >87% regardless of size or population. Glufosinate provided 90% or greater control of small plants but was less effective on
large plants especially with one glyphosate-resistant population. All three populations were highly susceptible (>95%) to clethodim, nicosulfuron + rimsulfuron, and paraquat.
Impacts
Addition of 2,4-D or Clarity to glyphosate will improve control of glyphosate-resistant horseweed and will increase yields 18 to 39% depending on year and horseweed density. The usefulness of glufosinate for early pre-plant burndowns for horseweed control may be limited by air temperature. Tillage as late as November may not sufficiently control later emerging horseweed. Follow-up chemical applications will still be required to remove flushes that emerge following tillage. Glyphosate tolerant Italian ryegrass could potentially pose a larger threat to crop production than glyphosate-resistant horseweed because there are few affordable control alternatives and many herbicides that are added to glyphosate to control resistant horseweed reduce the control of ryegrass.
Publications
- Poston, D.H., V.K. Nandula, C.H. Koger, and R.M. Griffin. 2006. Impact of preemergence herbicides on growth and yield of early-planted soybean in the Mississippi Delta. Weed Technol. In final stages of review.
- Nandula, V.K., K.N. Reddy, A.R. Rimando, S.O. Duke, and D.H. Poston. 2006. Glyphosate metabolism in glyphosate-resistant and susceptible soybean and canola. Proc. Amer. Chem. Soc. San Francisco, CA.
- Prince, J.M., D.R. Shaw, L.A. Farno, D.H. Poston, C.H. Koger, T.W. Eubank, and C.J. Gray. 2006. Post-applied residual herbicide in an early-planted glyphosate-resistant soybean system. Proc. South. Weed Sci. Soc. 59:28.
- Eubank, T.W., D.H. Poston, C.H. Koger, V. Nandula, and M.E. Kurtz. 2006. Annual grass control in Mississippi soybean with KIH-485 and other residual herbicides. Proc. South. Weed Sci. Soc. 59:30.
- Jones, E.J., D.H. Poston, G.D. Wills, and R.E. Mack. 2006. Effect of chlorophenoxy-Roundup Weathermax tankmixes on glyphosate-resistant horseweed [Conyza canadensis (L.) Cronq.]. Proc. South. Weed Sci. Soc. 59:54.
- Koger, C.H., D.H. Poston, T.W. Eubank, and V. Nandula. 2006. Emergence patterns and residual weed control with Sequence. Proc. South. Weed Sci. Soc. 59:55.
- Nandula, V. K., D. H. Poston, T. W. Eubank, C. H. Koger, and K. N. Reddy. 2006.Differential response to glyphosate in Italian ryegrass (Lolium multiflorum) populations from Mississippi. Accepted (12/4/06) for publication in Weed Technology.
- Nandula, V. K., D. H. Poston, K. N. Reddy, and C. H. Koger. 2006. Formulation and adjuvant effects on uptake and translocation of 14C-clethodim in bermudagrass (Cynodon dactylon). Accepted (10/13/06) for publication in Weed Science.
- D. H. Poston, V. K. Nandula, R. M. Griffin, D. R. Shaw, and M. C. Smith. 2006. Weed control alternatives in very early-maturing Mississippi soybean. Accepted for publication in Crop Management.
- Poston, D.H., V.K. Nandula, R.M. Griffin, and C.H. Koger. 2006. Texasweed (Caperonia palustris) control in soybean with postemergence herbicides. Weed Technol. In final stages of review.
- Nandula, V. K., K. N. Reddy, A. M. Rimando, S. O. Duke, and D. H. Poston . 2006. Glyphosate resistant and susceptible soybean (Glycine max) and canola (Brassica napus) dose response and metabolism relationships with glyphosate. Submitted to Journal of Agricultural and Food Chemistry. In Review.
- Nandula, V.K., T.W. Eubank, D.H. Poston, C.H. Koger, and K.N. Reddy. 2006. Investigations into suspected resistance of Italian ryegrass to glyphosate in Mississippi. Proc. South. Weed Sci. Soc. 59:172.
- Eubank, T.W., D.H. Poston, C.H. Koger, V.K. Nandula, D.R. Shaw, and D.B. Reynolds. 2006. Germination and emergence of horseweed (Conyza canadensis) and its control utilizing tillage and herbicides. Proc. South. Weed Sci. Soc. 59:87.
- Eubank, T.W., V.K. Nandula, D.H. Poston, C.H. Koger, and K.N. Reddy. 2006. Factors effecting germination of horseweed. Proc. Weed Sci. Soc. Amer. 46:25.
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Progress 01/01/05 to 12/31/05
Outputs
KIH-485 applied preemergence at rates of 0.15 lb and 0.225 lb ai/A and 2.54 lb ai/acre s-metolachlor generally provided better annual grass control than other treatments evaluated. Single postemergence applications of KIH-485 mixed with glyphosate were safe to soybean and provided late-season grass control and soybean yield comparable to two applications of glyphosate. Glyphosate resistant horseweed has been documented as far south as Greenville, MS. Glyphosate provided 60 to 74% horseweed control 4 WAT. The addition of 2,4-D or Clarity to glyphosate increased control to >90%. Glyphosate did stunt horseweed plants. When glyphosate burndowns were followed by 2 in-season glyphosate applications, soybean yields were similar to the treatments that provided the best horseweed control. More than 15 horseweed plants per square meter were required to reduce yields compared to the best treatments when glyphosate-based burndown programs were used. Horseweed plants treated with
paraquat quickly recovered and by 4 WAT paraquat alone provided only 55% control. Paraquat + Sencor was the only treatment that provided greater than 90% horseweed control and was consequently the highest yielding treatment. Paraquat + Clarity produced similar yields but did not provide equivalent weed control. Soybean yield was reduced more than 30 bu/acre when more than 15 paraquat-treated plants were allowed to compete with soybean. Glufosinate applied when the air temperature was 79 degrees F provided 96% horseweed control and soybean yields were similar with all glufosinate-based treatments evaluated. A survey of glufosinate applications made in 4 different trials revealed horseweed control ratings of 78, 86, 89, and 96% when applications were made at 64, 70, 73, and 79 degrees F, respectively. Horseweed control with glyphosate, paraquat, and glufosinate was 60, 40, and 76%, respectively. Control with paraquat and glufosinate tended to be better with AI nozzles. With glyphosate,
control did not differ significantly between nozzles. Better control with the contact herbicides using AI nozzles may be explained by canopy penetration by heavier droplets. Most horseweed germinated from September through November with smaller flushes emerging March through May. Tillage in March reduced horseweed populations 90% compared to 50, 70, and 80% with tillage in September, November, and January, respectively. Italian ryegrass with 3-fold tolerance to glyphosate has been identified. Glyphosate completely controlled a known-susceptible population. Control of resistant plants by glyphosate decreased from 80 to 98% for small sized plants to 44 to 79% for larger plants. Diclofop provided 38% control of small plants from one resistant population and was ineffective on large plants from all three populations. Control with mesosulfuron was >87% regardless of size or population. Glufosinate provided 90% or greater control of small plants but was less effective on large plants
especially with one glyphosate-resistant population. All three populations were highly susceptible (>95%) to clethodim, nicosulfuron + rimsulfuron, and paraquat.
Impacts
KIH-485 may provide the residual control needed to substantially reduce annual grass infestations at harvest in early-maturing soybean thereby reducing the need for harvest aids. Addition of 2,4-D or Clarity to glyphosate may be needed to control glyphosate resistant horseweed, which can reduce yield at a density of more than 15 horseweed plants per square meter. Paraquat alone did not provide adequate horseweed control. Addition of Sencor or Clarity increased control to acceptable levels. Yield reduction of 30 bu/acre was documented when 15 or more paraquat-treated plants competed with the soybean. The usefulness of glufosinate for early pre-plant burndowns for horseweed control may be limited by air temperature. Droplet size relative to canopy density may be more closely correlated to control with contact herbicides than the type of nozzles utilized. Tillage as late as November may not sufficiently control later emerging horseweed. Follow-up chemical applications
will still be required to remove flushes that emerge following tillage. Glyphosate tolerant Italian ryegrass could potentially pose a larger threat to crop production than glyphosate-resistant horseweed because there are few affordable control alternatives and many herbicides that are added to glyphosate to control resistant horseweed reduce the control of ryegrass.
Publications
- Nandula, V. K., K. N. Reddy, S. O. Duke, and D. H. Poston. 2005. Glyphosate-resistant weeds: current status and future outlook. Outlooks on Pest Management. Online Journal. DOI: 10.1564/16aug11
- Poston, D. H., C. E. Snipes, T. W. Eubank, and S. P. Nichols. 2005. Flame weed control for organically grown soybean in Mississippi. Proc. South. Weed Sci. Soc. 58:35.
- Poston, D. H., J. C. Sanders, T. W. Eubank, H. P. Wilson, D. M. Dodds, and D. R. Shaw. 2005. Interactions between manganese fertilizers and glyphosate. Proc. South. Weed Sci. Soc. 58:39.
- Sanders, J. C., D. H. Poston, D. M. Dodds, K. W. Bradley, T. W. Eubank, C. M. Whaley, H. P. Wilson, and D. R. Shaw. 2005. Influence of manganese formulations on glyphosate efficacy in soybean. Proc. South. Weed Sci. Soc. 58:37.
- Nandula, V., D. H. Poston, C. H. Koger, and T. W. Eubank. 2005. Horseweed control with glyphosate-, glufosinate-, and paraquat-based herbicide programs. Proc. South. Weed Sci. Soc. 58:40.
- Poston, D. H., C. H. Koger, and T. W. Eubank. 2005. Use of residual herbicides in pre-plant weed control programs for early-planted soybean in Mississippi. Proc. South. Weed Sci. Soc. 58:41.
- Eubank, T. W., D. H. Poston, and C. H. Koger. 2005. Remote sensing as a decision-making tool for desiccation of Mississippi soybean. Proc. South. Weed Sci. Soc. 58:46.
- Koger, C. H., D. H. Poston, and T. W. Eubank. 2005. Factors affecting germination of horseweed (Conyza Canadensis). Proc. South. Weed Sci. Soc. 58:218.
- Eubank, T. W., D. H. Poston, C. H. Koger, C. J. Gray, D. R. Shaw, and E. W. Palmer. 2005. Evaluation of Sequence applied post-emerge in early-maturing Mississippi soybean. Proc. South. Weed Sci. Soc. 58:73.
- Prince, J. M., D. R. Shaw, C. J. Gray, W. A. Givens, and D. H. Poston. 2005. Incorporating residual grass herbicides into early-planted glyphosate-resistant soybean production. Proc. South. Weed Sci. Soc. 58:75.
- Smith, K. L., L. E. Steckel, and D. H. Poston. 2005. Management challenges associated with glyphosate-resistant horseweed control in cotton and soybean. Proc. South. Weed Sci. Soc. 58:231.
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Progress 01/01/04 to 12/30/04
Outputs
Studies were conducted at Stoneville, MS and Painter, VA to determine the impact of various Mn fertilizer formulations on glyphosate efficacy. Postman Mn fertilizer formulation significantly reduced weed control by glyphosate and antagonism increased with Mn concentration. Increasing glyphosate rate overcame Mn antagonism to some extent. Glyphosate formulation did not influence weed control. Studies were conducted to evaluate flame cultivation for soybean weed control. In April-planted studies, flame weed control produced soybean yields of 48 bu/A that were similar to the 50 bu/A that was achieved with two applications of glyphosate. In May plantings, soybean yields with flame cultivation equaled those achieved with the glyphosate-resistant program only 1 of 2 years. Soybeans grown organically using flame weed control would have to be sold for a premium of approximately $2 per bushel to equal returns that would occur using the glyphosate only system. Studies were
conducted to evaluate the efficacy and economics of residual herbicides used as part of glyphosate-based burndown programs. Plots treated with residual herbicides + glyphosate consistently had less than 10% groundcover at planting. Soybean yields and net returns were highest where residual herbicides were used. Yield increased in nontreated plots with an at-planting burndown. Herbicide treated plots generally did not. Sequence applied post-emergence to early-maturing soybean at the V5-V6 growth stage provided better late-season annual grass control than applications made at V3-V4. Annual grass control was similar with sequence across all rates evaluated. Yields were similar in plots treated with 1 late application of glyphosate, 2 applications of glyphosate, and Sequence. Sequence-treated plots were cleaner at harvest than plots treated with glyphosate alone. Studies were conducted to evaluate control of glyphosate-susceptible horseweed with nonselective herbicide programs. Glyphosate
provided excellent horseweed control, whereas, glufosinate and paraquat required a tank-mix partner to provide complete control. Adding 2,4-D or dicamba to glufosinate provided complete horseweed control. Only the addition of dicamba to the paraquat treatment provided complete control. Flumioxazin and metribuzin reduced horseweed control by glyphosate, but provided greater than 90% control when mixed with glufosinate or paraquat. Treatments containing flumioxazin, [sulfentrazone + chlorimuron], or sulfentrazone provided the most consistent residual control. Field studies were conducted to investigate the effects of soil temperature, tillage timing, and non-selective herbicide timing on horseweed emergence. Extensive germination occurred in September and October of both years. Horseweed germinated when soil temperatures were above 10 C, and no differences were observed in germination patterns between susceptible and resistant populations. Tillage and fall tillage followed by a spring
burndown reduced densities compared to nontreated plots, but new flushes emerged following each program.
Impacts
Selecting the appropriate Mn fertilizer formulation will eliminate glyphosate antagonism. Flame weed control can be used to profitably produce organically grown soybean thereby creating a specialty market for small producers. Incorporating residual herbicides into glyphosate-based burndown programs for early-planted soybean in Mississippi could improve planting efficiency and potentially increase yields 5 to 8 Bu/Acre and net returns $22 to 34/A on highly productive soils. Using Sequence postemergence will reduce grass biomass at harvest in early-maturing soybean; thereby improving harvest efficiency and eliminating the need for pre-harvest desiccants. Based on horseweed emergence patterns, residual herbicides will likely be needed to prevent weed flushes between burndown and planting.
Publications
- Koger, C. H., D. H. Poston, and K. N. Reddy. 2004. Effect of glyphosate spray coverage on control of pitted morningglory (Ipomoea lacunosa). Weed Technol. 18:124-130.
- Spinks, B. L., D. H. Poston, and G. L. Sciumbato. 2004. Impact of foliar fungicides on soybean yield and net returns. Proc. South. Soybean Dis. Workers Conference.
- Snipes, C. E., D. H. Poston, and S. P. Nichols. 2004. Impact of flame weeding in cotton and soybean. Proc. South. Weed Sci. Soc. 57:346.
- Poston, D. H., C. H. Koger, M. A. Blaine, and B. L. Spinks. 2004. Winter weed management in early-planted Mississippi soybean. Proc. South. Weed Sci. Soc. 57:12.
- Poston, D. H., C. H. Koger, and B. L. Spinks. 2004. Pitted morningglory control, survival, and seed production following applications of glyphosate and glyphosate tank mixtures. Proc. South. Weed Sci. Soc. 57:280-281.
- Spinks, B. L., D. H. Poston and C. H. Koger. 2004. Managing annual grass populations in early-maturing Mississippi soybean. Proc. South. Weed Sci. Soc. 57:336-337.
- Koger, C. H., D. H. Poston, R. M. Hayes, and R. F. Montgomery. 2004. Glyphosate-resistant horseweed (Conyza canadensis) in Mississippi. Weed Technol. 18:820-825.
- Koger, C. H., K. N. Reddy, and D. H. Poston. 2004. Factors affecting seed germination, seedling emergence, and survival of Texasweed (Caperonia palustris). Weed Sci. 52:989-995.
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Progress 01/01/03 to 12/31/03
Outputs
Studies were conducted to assess the impact of single glyphosate applications, sequential glyphosate applications, and glyphosate tank mixtures on control of different sized pitted morningglory plants. Glyphosate at 0.94 and 0.75 lb ae/A was required to provide maximum control of vining plants and 3- to 5-leaf plants, respectively. Control with 0.75 lb ae/A fb 0.56 lb ae/A was generally similar to the best single applications. Tank mixing chlorimuron or cloransulam with 0.56 lb ae/A glyphosate generally did not improve control compared to 0.56 lb ae/A glyphosate alone. Using 0.94 or 1.12 lb ae/A glyphosate as a single application or a sequential application of 0.75 lb ae/A fb 0.56 lb ae/A essentially eliminated seed production. Field studies were conducted to evaluate the efficacy and economics of flame cultivation for weed control in organically grown soybean. Weed control with flame cultivation ranged from 75 to 93 percent depending on species evaluated. Control
with flame cultivation was generally higher than with cultivation only. Morningglories and annual grasses were the most difficult to control with flame cultivation. Morningglory and sicklepod control with flame cultivation was similar to or better than that provided by the Roundup Ready and conventional weed control systems, respectively. Cultivation and flame cultivation reduced labor costs associated with hand-weeding 18 and 39 percent, respectively. Soybean yields from April-planted studies on silt loam soils were 33, 50, and 63 Bu/A for untreated, flame-weeded, and Roundup Ready plots, respectively. Estimated returns from these studies look promising. Field studies were conducted to evaluate the impact of postemergence metolachlor, tillage, and row spacing on late-season annual grass infestations in early-maturing soybean. Annual grass biomass was 31 to 38% and 58 to 70% lower in plots treated with 0.84 kg/ha glyphosate + 1.8 or 1.3 kg/ha s-metolachlor compared to plots treated
with glyphosate alone in 2002 and 2003, respectively. Using residual grass herbicides postemergence in glyphosate only weed control programs may reduce annual grass populations in early-maturing soybean. There was 51 and 63% less grass biomass in 38 cm rows than in 76 cm rows in 2002 and 2003, respectively. Narrowing row spacings was the most cost-effective strategy to reduce late-season annual grass infestations. Studies were conducted to determine the efficacy and economics of twelve herbicide programs for winter weed management in April-planted soybean where a 3-pass production system (1-pre-plant burndown, 2-plant in April, 3-one postemergence glyphosate application) was utilized. Glyphosate + 2,4-D, glyphosate + sulfentrazone + chlorimuron, glyphosate + 2,4-D + oxyfluorfen, and glyphosate + flumioxazin provided greater than 90% control of all vegetation. Plots with these treatments had less than 10% green groundcover at planting in mid-April. Maximum net returns were achieved
with glyphosate + flumioxazin and glyphosate + sulfentrazone + chlorimuron. Averaged across years, the best application date appeared to be late February.
Impacts
Glyphosate rates of at least 0.94 lb ae/A will provide consistent control of all sizes of pitted morningglory and significantly reduce the number of pitted morningglory seed in the soil seed bank. Flame weed control can be used to profitably produce organically grown soybean thereby creating a specialty market for small producers. Incorporating residual herbicides into glyphosate-based burndown programs for early-planted soybean in Mississippi could improve planting efficiency and potentially increase yields 3 to 6 Bu/Acre and net returns $20 to 30/Acre on highly productive soils. Using metolachlor in tank mix with postemergence glyphosate applications or reducing row spacing compared to plots treated with glyphosate alone g from 30 to 15 inches in early-maturing soybean could reduce grass biomass at harvest by 50 percent; thereby improving harvest efficiency and eliminating the need for pre-harvest herbicide applications.
Publications
- Bailey, W.A., D.H. Poston, H.P. Wilson, and T.E. Hines. 2003. Manganese reduces weed control from glyphosate. Weed Sci. Soc. Amer. Abstr.43:82-83.
- Koger, C.H. and D.H. Poston. 2003. Control of pitted morningglory (Ipomoea lacunosa) is related to glyphosate spray coverage. Weed Sci. Soc. Amer. Abstr.43:77-78.
- Poston, D.H. and C.H. Koger. 2003. Pitted morningglory (Ipomoea lacunosa) survival following applications of glyphosate and glyphosate tank mixtures. Weed Sci. Soc. Amer. Abstr.43:70.
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Progress 01/01/02 to 12/31/02
Outputs
Studies were conducted to evaluate the impact of PRE herbicides on growth, development, and yield of soybean planted in April. DP 4748S appeared more tolerant than DP 3478 to most PRE broadleaf herbicides. Full rates of Canopy XL and Sencor reduced yield both years. Reduced rates of PRE broadleaf herbicides alone generally did not reduce yield. However, mixing PRE broadleaf herbicides with Prowl or Dual often increased injury and sometimes reduced yield. In 2001, yield was reduced 4% by Prowl and full rates of Sencor, Canopy XL, and Python reduced yields 13, 9, and 6% compared to the untreated control, respectively. Soil-applied weed management programs in early-planted soybean will likely involve matching tolerant soybean varieties to specific herbicide programs. PRE broadleaf herbicides should be applied at reduced rates and alone in April-planted soybean. Scepter and Python were the safest herbicides to use in conjunction with PRE grass herbicides in early-planted
soybean. Many treatments did not reduce yield but impeded growth and development, which would likely reduce crop competitiveness with weeds. Studies were conducted to determine optimum timings for POST glyphosate applications in Roundup Ready soybean planted at various dates. In 2001, weed control was 5 to 9% higher with 15-inch row spacings than with 30-inch row spacings. Sequential applications were often necessary with 30-inch rows to achieve weed control similar to single applications in 15-inch rows. Maximum yield averaged across row spacings was achieved with a single glyphosate application 6 and 5 WAP for March 27- and April 20-planted soybeans, respectively. For May 3-planted soybeans, maximum yield was obtained with single glyphosate applications 4 and 5 WAP in 15- and 30-inch row spacings, respectively. In 2002, maximum soybean yield occurred in April-planted soybean with single glyphosate applications made 4 or 5 WAP. In May-planted soybean, maximum yields occurred with
single applications made 3 or 4 weeks after planting. Sequential glyphosate applications may not be needed to maximize yield in soybean fields planted in narrow rows prior to May 1 in the Mississippi delta. Therefore, weed management costs could be considerably less in early-planted soybean systems compared to more traditional systems. Studies were conducted to evaluate the impact of postemergence metolachlor, tillage, and row spacing on late-season annual grass infestations in early-maturing soybean. Annual grass biomass was 31 to 38% lower in plots treated with 0.84 kg/ha glyphosate + 1.8 or 1.3 kg/ha s-metolachlor compared to plots treated with glyphosate alone. Annual grass biomass at harvest was not influenced by tillage, but was 51% less in 38-cm rows compared to 76-cm rows. Postemergence residual grass herbicides may be helpful in managing annual grass populations in early-maturing soybean. Initial results from this study indicate that the most immediate and effective strategy
for producers to implement to combat late-season annual grass problems in glyphosate-resistant soybean is narrow row spacings.
Impacts
Reducing PRE herbicide use and rates in early-planted soybeans or matching tolerant varieties to herbicide programs should improve yield in early-planted soybeans and improve the crop's ability to compete with weeds. Sequential glyphosate applications may not be required for Roundup Ready soybeans planted in narrow rows prior to May 1 some years. Soybean producers would save $5 to 7 million dollars in weed control costs annually if only one POST glyphosate application was made on 50% of Mississippi's early-planted soybean acres. Early planting dates will allow producers more time to make POST herbicide applications making it easier to farm larger acreages with less labor and equipment. By narrowing row spacings and/or using post metolachlor applications in early-maturing soybean, producers can reduce late-season grass infestations in early-maturing soybean 30 to 50 percent thereby increasing harvest efficiency and reducing the likelihood of using pre-harvest
desiccants.
Publications
- Griffin, R.M., D.H. Poston, M.A. Blaine, and D.R. Shaw. 2002. Postemergence Texasweed control in Mississippi soybeans. Proc. South. Weed Sci. Soc. 55:204.
- Griffin, R.M. 2002. Weed Control in Early-maturing Soybean Grown in MS at Various Row Spacings and Planting Dates. M.S. Thesis, Mississippi State University.
- D.H. Poston, R.M. Griffin, and R.T. Coleman. 2002. Influence of preemergence herbicides on growth, development, and yield of early-planted soybeans in the MS delta. Proc. South. Weed Sci. Soc. 55:41-42.
- D.H. Poston, R.M. Griffin, and R.T. Coleman. 2002. Interrelations of row spacing and glyphosate application timing in roundup ready soybeans planted at various dates in the MS Delta. South. Weed Sci. Soc. 55:150.
- Griffin, R.M., D.H. Poston, D.R. Shaw, and F.S. Kelley. 2002. Weed control in maturity group IV soybean grown in MS at various row spacings and planting dates. Proc. South. Weed Sci. Soc. 55:150-151.
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Progress 01/01/01 to 12/31/01
Outputs
Studies were conducted to: 1) evaluate postemergence (POST) Texasweed control with conventional herbicides, glyphosate, and tank mixtures of glyphosate with conventional herbicides; 2) evaluate the impact of preemergence (PRE) herbicides on growth, development, and yield of soybeans planted in early-April; 3) determine optimum timings for postemergence (POST) glyphosate applications in Roundup Ready soybeans planted late-March, mid-April, and early-May in 15- and 30-inch rows; and 4) evaluate various herbicide programs in maturity group (MG) IV soybeans planted at various dates in 7.5- and 15-inch row spacings. Texasweed control 4 WAT with diphenylether herbicides was 76 -88% in 2000 when herbicide applications were made on cotyledon to 3-leaf Texasweed plants, but ranged from 50 to 71% in 2001 when applications were made on larger plants. Texasweed control with ALS-inhibiting herbicides was less than 60% both years. More consistent control over years was observed
with glyphosate and control was generally similar to control with diphenylether herbicides. Tank mixing conventional herbicides with 0.75 lb ai acre-1 glyphosate generally did not increase control except when plants exceeded the 3-leaf stage. Excellent control of 1- to 2-leaf Texasweed plants was observed with 0.5 to 1.5 lb ai acre-1 glyphosate, but 1.0 lb ai acre-1 or more was needed to control larger plants. Excellent (>90%) Texasweed control occurred with fomesafen except with low rates applied to 4-leaf Texasweed. DP 4748S planted in early-April was more tolerant to Canopy XL, Sencor, and Python than DP 3478. Harvest height of DP 3478 was reduced by nearly all PRE herbicides, but harvest heights for DP 4748S were not affected. Soybean yields were reduced 4, 13, 9, and 6% by full rates of Prowl, Sencor, Canopy XL, and Python, respectively. No yield reductions were recorded in plots treated with reduced rates of PRE broadleaf herbicides. In glyphosate timing studies, total weed
control was 5 to 9% higher with 15-inch row spacings than with 30-inch spacings. Weed control was 92% or greater with single glyphosate applications made 6, 5, and 5 WAP in soybeans planted in 15-inch rows on March 27, April 20, and May 3, respectively. With 30-inch row spacings, sequential glyphosate applications 5 fb 7, 3 fb 5, and 3 fb 5 WAP were required to achieve 90% or greater weed control for March 27-, April 20-, and May 3-planted soybeans, respectively. For March 27-planted soybeans, maximum yield averaged across row spacings was achieved with a single glyphosate application 6 WAP. For April 20-planted soybeans, maximum yield occurred with single glyphosate applications 5 WAP in 15- and 30-inch rows. For May 3-planted soybeans, maximum yield was obtained with single glyphosate applications 4 and 5 WAP in 15- and 30-inch row spacings, respectively. Postemergence treatments were required 35 days after planting (DAP) for the early-April plantings, 24 DAP for the mid-April
plantings, and 14 DAP for the early-May plantings. Earlier planting dates allowed postponement of postemergence herbicide treatments.
Impacts
Fomesafen and glyphosate will control Texasweed and possibly slow down the spread of this weed in rice and soybean fields. Savings in herbicide costs can be realized if herbicide applications are made to Texasweed plants at the 3-leaf stage or smaller. Reducing PRE herbicide use in early-planted soybeans or matching tolerant varieties to herbicide programs should improve yield in early-planted soybeans and improve the crop's ability to compete with weeds. Sequential glyphosate applications may not be required for Roundup Ready soybeans planted in narrow rows prior to May 1 some years. Soybean producers would save at least $5 million dollars in weed control costs annually if only one POST glyphosate application was made on 50% of Mississippi's early-planted soybean acres. Early planting dates will allow producers more time to make POST herbicide applications making it easier to farm larger acreages with less labor and equipment.
Publications
- Poston, D.H., Shaw, D.R., Smith, C., and Griffin, R.M. 2001. Weed control alternatives for maturity group III soybeans grown in Mississippi. Proc. South. Weed Sci. Soc. 54: 48.
- Griffin, R.M., Shaw, D.R., Poston, D.H., Grant, A.B. 2001. Effect of planting date and row spacing on group IV soybean weed control. Proc. South. Weed Sci. Soc. 54: 177.
- Griffin, R.M., Poston, D.H., Shaw, D.R., Blaine, M.A., and Flint, S.G. 2001. Postemergence control of Texasweed in soybean. Proc. South. Weed Sci. Soc. 54: 50.
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