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Annual Report of Progress
to the
MISSISSIPPI SOYBEAN PROMOTION BOARD
for 1998

 
Project Title: Assessment and Optimization of Efficacy and Economics of Herbicide-Tolerant Weed Control Programs
Project Leader: David R. Shaw, Plant and Soil Sciences Department
Other Participants:

 

 Charles E. Snipes, Delta Research and Extension Center
David H. Laughlin, Agricultural Economics Department

Objectives

  1. Compare Roundup Ready weed control/variety systems to conventional systems for efficacy and economics.
  2. Determine the potential of Roundup-, Liberty-, and sulfonylurea-tolerant soybean cultivars as weed management tools in Mississippi soybeans compared to conventional herbicide systems in various row spacings and tillage Systems.
  3. Determine efficacy of Roundup on the perennial weeds redvine and yellow nutsedge in Roundup Ready soybeans in the season of application, on tuber and root viability, and on infestations the following year.

 

Significant Accomplishments

1.

Studies were conducted in 1997 and 1998 to evaluate the efficacy and economics of Roundup Ready and conventional soybean Systems. The three highest yielding Roundup Ready and conventional soybean cultivars were chosen each year for two Mississippi locations: Shelby (irrigated, Sharkey clay soil) and Brooksville (non-irrigated, Black Belt clay soil). Cultivars were selected based on the 1996 and 1997 Mississippi Soybean Variety Trials for these locations and soil types. Treatments within each cultivar herbicide system included untreated, reduced rate, labeled rate, and high level of input.

Pitted morningglory and hemp sesbania were the predominant species at all locations. Control of hemp sesbania was different between the two years at both locations. In 1997, Roundup controlled hemp sesbania more than the comparable conventional system in most instances. However, in 1998, control was higher with conventional herbicides. Within the Roundup Ready system, control was lower with reduced rates compared to labeled rates or high input levels. Within the conventional system, increased rates did not increase control of hemp sesbania in most instances. Control of pitted morningglory was greater in most instances when high levels of input were used in comparison to labeled and reduced rates, regardless of system. At Shelby, reduced rates of conventional herbicides controlled pitted morningglory more than the comparable Roundup Ready system. At labeled rates or high input levels, pitted morningglory control was at least 85%, regardless of the program. Reduced and labeled rates did not control pitted morningglory, regardless of the system involved.

 

2.

Field studies were conducted at the Delta Research and Extension Center at Stoneville, MS, to evaluate the effects of row spacing in Roundup Ready and Liberty Link weed management systems. Asgrow 5901RR, a Roundup Ready cultivar of the maturity group V, and Asgrow 5547LL, a MG V with the Liberty Link genetics, were used in this study. Treatments for the Roundup Ready System included various rates of Roundup alone or following l/2X or 1X Squadron, and Squadron followed by 1.5 pt/A Storm. Treatments for the Liberty Link system were similarly structured. Row spacing of 38 and 76 cm were used with both cultivars.

Sicklepod, pitted morningglory, and hemp sesbania were the predominant species throughout the study. Squadron followed by Roundup controlled pitted morningglory more than Roundup alone in both 38 and 76 cm rows 8 weeks after planting (WAP). Squadron followed by Liberty did not increase pitted morningglory control compared to Liberty alone in either row spacing. Squadron followed by Liberty controlled sicklepod more than any of the treatments of Liberty alone. Roundup at 1.5 pt/A followed by 1 pt/A controlled more sicklepod than any of the Squadron followed by Roundup treatments. Hemp sesbania was controlled more with the conventional herbicide treatments compared to the Roundup treatments. Liberty at 0.38 lb/A followed by 0.38 lb/A Liberty controlled hemp sesbania more than the conventional herbicide treatment. There was no difference in yield between any of the treatments in the study.

In the herbicide combinations research, soil-applied herbicides did not increase broadleaf signalgrass, sicklepod, or hemp sesbania control compared to the sequential glyphosate treatment. Canopy XL followed by Roundup controlled pitted morningglory better than Roundup alone. Conversely, soil-applied herbicides followed by one Roundup applications controlled sicklepod less than two applications of Roundup. At least 1.5 pt/A Roundup was required to control hemp sesbania when following a soil-applied herbicide. Two applications of Roundup controlled hemp sesbania as well as or better than soil-applied followed by Roundup.

 

3.

Field studies were conducted in 1998 at the Black Belt Branch Experiment Station, Brooksville, MS, to evaluate control of yellow nutsedge using conventional herbicide programs, as well as glyphosate at various rates and application timings. Conventional herbicide treatments applied were metolachlor alone, bentazon alone, metolachlor + imazaquin followed by bentazon, and metolachlor + sulfentrazone + chlorimuron followed by bentazon. Postemergence applications of bentazon were applied 7 weeks after planting (WAP). Two sequential applications of glyphosate were applied at 3 and 7 WAP at rates of 0.84 followed by 0.56 kg ai/ha, 1.1 followed by 1.1 kg/ha, and 0.42 followed by 0.28 kg/ha. Glyphosate was also applied using three sequential applications at 3, 7, and 10 WAP at rates of 0.84 followed by 0.56 followed by 0.56kg/ha, 1.1 followed by 1.1 followed by 1.1 kg/ha, and 0.42 followed by 0.28 followed by 0.28 kg/ha. Visual ratings were then used to determine control.

At 3 weeks after planting, metolachlor PRE controlled yellow nutsedge 65%. Other preemergence treatments controlled yellow nutsedge at least 81%. At 6 WAP, preemergence treatments controlled similar to the 3 WAP evaluation, while treatments containing one application of glyphosate controlled yellow nutsedge at least 91%. At 10 WAP, treatments containing two applications of glyphosate controlled yellow nutsedge 70-80%. At 13 WAP, treatments containing glyphosate with three sequential applications at 0.84 followed by 0.56 followed by 0.56 kg/ha and 1.1 followed by 1.1 followed by 1.1 kg/ha controlled yellow nutsedge at least 87%. Remaining glyphosate treatments controlled yellow nutsedge 73-80%. Metloachlor PRE or bentazon POST alone controlled yellow nutsedge approximately 63%. Control ratings for other PRE/POST combination treatments ranged from 71-77%.

Two experiments in the Mississippi Delta were designed as a two-year study conducted to evaluate control of redvine in Roundup Ready soybean. Data recorded include live redvine stem counts per square meter as well as percent groundcover for live plants. The objective of this study is to determine long term effects of glyphosate applied in-season using various rates and timings. Rates of Roundup Ultra range from 0.50 lb ni/A to 2 lb ai/A at application timings of 1 week preplant, post 3, 4, 5, and 7 weeks after planting, and preharvest applications. An additional treatment of 2 lb ai/A Banvel SGF was used as a pre harvest treatment. These treatments will not be applied the second year of the experiment. Additional stem counts and ground cover ratings will be conducted several times during 1999. The data will then be evaluated to determine the long-term effect of the various treatments.

Control from a short-term standpoint was determined on the basis of comparison to the untreated check for both groundcover and live stem numbers. The treatments containing Gramoxone Extra burndown and two applications of Roundup Ultra at 4 WAP and 7 WAP controlled redvine stems and groundcover 23% and 46%, respectively. Treatments containing Roundup Ultra burndown with the same post treatments controlled redvine stems 91% and reduced groundcover 90%. Treatments containing Roundup Ultra burndown followed by POST applications of Roundup Ultra at 3 WAP and 5 WAP (considered the standard application rate based on annual weed control research) reduced live stems by 71% and groundcover 88%. One trend noted was as the number of applications of Roundup Ultra increased, control of both live stems per meter and groundcover increased. Treatments containing the maximum labeled rate of Roundup Ultra for in-crop and preharvest applications controlled live stems and reduced groundcover 99% and 93%, respectively.

Publications

  1. Akin, D. S., D. R. Shaw, and G. W. Nice. 1999. Effects of Roundup Ultra and conventional herbicides on yellow nutsedge (Cyperus esculentus) in soybean. Proc. South. Weed Sci. Soc. 52:in press.
  2. Akin, D. S., D. R. Shaw, and J. L. Norris. 1999. Efficacy of ALS-inhibiting broadleaf herbicides tank-mixed with Roundup Ultra in Roundup Ready soybean. Proc. South. Weed Sci. Soc. 52:in press.
  3. Arnold, J. C., D. R. Shaw, and C. R. Medlin. 1998. Roundup Ready programs versus conventional programs: Efficacy, varietal performance, and economics. Proc. South. Weed Sci. Soc. 51:272.
  4. Arnold, J. C., D. R. Shaw, and J. L. Norris. 1999. Assessment of efficacy and economics in Roundup Ready versus conventional soybean programs. Proc. South. Weed Sci. Soc. 52:in press.
  5. Arnold, J. C., D. R. Shaw, and S. M. Schraer. 1997. Influence of application timing on efficacy of glyphosate in Roundup Ready¨ soybean. Proc. South. Weed Sci. Soc. 50:176.
  6. Bennett, A. C., D. R. Shaw, and D. S. Akin. 1999. Efficacy of diphenylether herbicides tank-mixed with glyphosate. Proc. South. Weed Sci. Soc. 52:in press.
  7. Bennett, A. C., D. R. Shaw, and S. M. Schraer. 1998. Effect of conventional herbicide programs and irrigation on glyphosate-tolerant soybean yield. Proc. South. Weed Sci. Soc. 51:270.
  8. Flint, S. G., J. C. Holloway, D. R. Shaw, and M. C. Smith. 999 Soil applied herbicide programs in a Roundup Ready system. Proc. South. Weed Sci. Soc. 52:in press.
  9. Medlin, C. R., D. R. Shaw, and A. Rankins, Jr. 1998. Preemergence herbicide systems in Roundup-Ready soybean. Weed Sci. Soc. Am. Abst. 38:1.11.
  10. Medlin, C. R., D. R. Shaw, and J. C. Arnold. 1998. Evaluation of pyrithiobac in STS systems. Proc. South. Weed Sci. Soc. 51:63.
  11. Medlin, C. R,., D. R. Shaw, and R. C. Scott. 1997. Herbicide tank mix combinations for weed control in Roundup-Ready¨ soybean. Weed Sci. Soc. Am. Abst. 37:244.
  12. Norris, J. L., D. R. Shaw, C. E. Snipes, and D. S. Akin. 1999. Influence of row spacing and residual herbicides on weed control in Roundup Ready and Liberty Link soybean. Proc. South. Weed Sci. Soc. 52:in press.
  13. Norris, J. L., C. E. Snipes, D. R. Shaw, and S. M. Schraer. 1999. Influence of row spacing in no-till and conventional soybean weed control programs. Proc. South. Weed Sci. Soc. 52:in press.
  14. Smith, M. C. D. R. Shaw, and M. W. Shankle. 1998. Optimization of glyphosate rate and application timing for weed control in Mississippi glyphosate-tolerant soybean. Weed Sci. Soc. Am. Abst. 38:1.22.
  15. Smith, M. C., D. R. Shaw, and A. C. Bennett. 1999. Interaction of glyphosate rate and initial application timing on season-long weed control in Roundup Ready soybean. Proc. South. Weed Sci. Soc. 52:in press.
  16. Smith, M. C., D. R. Shaw, and S. M. Schraer. 1998. Soybean weed control with Strongarm, FirstRate, and Frontrow. Proc. South. Weed Sci. Soc. 51:62.
  17. Smith, M. C., D. R. Shaw, and S. M. Schraer. 1999. Efficacy of soil-applied residual herbicides in Mississippi glyphosate-tolerant soybean. Weed Sci. Soc. Am. Abst. 39:in press.
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