Annual Report of Progress
to the
MISSISSIPPI SOYBEAN PROMOTION BOARD
for 1996

Objectives

1. Determine the relative density of the five most troublesome pre-harvest weeds necessary to require desiccation treatments.
2. Determine the impact of relative maturity and soybean height on requirements for desiccation treatments.
3. Evaluate alternative herbicide combinations to optimize efficacious and economical weed desiccation.
4. Determine the impact of weed densities, pre-harvest desiccation treatments, and soybean height and maturity on weed seed production, germination, and vigor.

Publications

Bennett, A. C., D. R. Shaw, W. L. Barrentine, J. M. Ellis, and A. Rankins, Jr. 1996. Effect of soybean pre-harvest herbicides on weed seed production and viability. Proc. South. Weed Sci. Soc. 49:28.

Bennett, A. C., D. R. Shaw, J. M. Ellis, and M. W. Shankle. 1997. Effect of cultivar and herbicide treatment on weed seed production and viability in Group IV soybean. Proc. South. Weed Sci. Soc. 50:in press.

Bennett, A. C., D. R. Shaw, M. C. Smith, andW. L. Barrentine. 1997. Effectofpreharvest herbicides on weed seed production and viability in Group IV soybean. Weed Sci. Soc. Am. Abst 37:in press.

Ellis, J. M., D. R. Shaw, W. L. Barrentine, and K. M. Bloodworth. 1996. Effect of non-competitive weed densities on soybean harvesting quality. Proc. South. Weed Sci. Soc. 49:190.

Ellis, J. M., D. R. Shaw, W. L. Barrentine, and E. P. Webster. 1996. Pre-harvest weed control in soybeans. Proc. South. Weed Sci. Soc. 49:29.

Ellis, J. M., D. R. Shaw, W. L. Barrentine, A. C. Bennett, and M. W. Shankle. 1997. The impact of relative rnaturity and soybean height on requirements for desiccation. Proc. South. Weed Sci. Soc. 50:in press.

Significant Accomplishments

Soybean seed counts were made before and after harvest from a 5 ft² area in each plot. Soybean seed weight (g/100 seed) was determined after harvest. Seed weight and the differences between seed present before and after harvest were used to det ermine the effect each density had on harvest efficiency. Percent foreign material, splits, and soybean seed damage was recorded. Also, soybean yield, moisture, test weight, and time to harvest each plot was evaluated.

Percent foreign material increased as weed densities increased. Soybean yield loss due to crop interference during harvest was not affected by increased densities, except for sicklepod. Combine speed was not significantly affected by weed density except f or common cocklebur at 1 per m of row. Increased densities resulted in higher moisture levels with common cocklebur and sicklepod, however; no effect was observed with hemp sesbania and ivyleaf morningglory.

Field studies were conducted at the Black Belt Branch Experiment Station near Brooksville, MS, Coastal Plain Branch Experiment Station near Newton, MS, and Delta Branch Experiment Station near Stoneville, MS to determine the effectiveness of several herbi cides alone or in combination for burndown of green weeds. Weeds evaluated were pitted morningglory, common cocklebur, spotted spurge, and sicklepod. Separate studies were also to determine the interactions between variety maturity and stature; early post emergence treatments, and pre-harvest treatments on weed control, soybean yield and quality, and weed seed production and viability.

Broadstrike/Dual was applied PRE and Poast Plus was applied POST to all plots to eliminate early season weed interference. Pre-harvest treatments included 0.25 lb/A Gramoxone Extra alone or with sodium chlorate at 3 or 6 lb ai/A; Roundup D-Pak at 1 lb ai/A alone or with sodium chlorate at 3 or 6 lb/A; Roundup D-Pak at 2 lb/A alone or with sodium chlorate at 3 lb/A; Goal at O.25and 0.5 lb ai/A; Goal at 0.25 lb/A with sodium chlorate at 3 and 6 lb/A; Buctril at 2 lb ai/A; Buctril at 1 lb/A with sodium ch lorate at 3 lb/A; and Ignite at 0.75, 1, and 1.25 lb ai/A. Burn-down applications were made two weeks before harvest and visual ratings were made one and two weeks after application. Soybean yield, moisture, and harvest time were recorded. Also, soybean s eed counts were made before and after harvest from a 5 ft² area in each plot. Soybean seed weight (g/100 seed) and the differences between seed present before and after harvest were used to determine the amount of soybean loss during harvest.

Soybean moisture was lowest when a preharvest desiccant was applied (14.0-14.3 %). Combine speed was greatest (3.4 km/h) when chlorimuron followed by paraquat plus sodium chlorate was applied, regardless of cultivar maturity or stature. Paraquat plus sodium chlorate increased soybean test weight except for the cultivar DK 4450 in 1996. Foreign material was significantly reduced in 1995 when chlorimuron was applied alone or followed by paraquat plus sodium chlorate for all cultivars. In 1996 this was only true for the cultivar Hartz 4994 and DPL 3478. There was no consistent increase or reduction in damaged soybean, soybean splits, combine ha rvesting efficiency, or soybean yield due to cultivar maturity and stature, weed management, and preharvest desiccation treatments.

Soybean cultivar had an effect on pitted morningglory seed production. Use of a late maturity, tall cultivar resulted in 65% greater pitted morningglory seed production compared to an early maturity, short soybean cultivar. EPOST application of chlorimuro n provided good hemp sesbania control, reducing seed production 70%. Cultivar affected seed weight of both pitted morningglory and hemp sesbania, with later maturing cultivars resulting in heavier, more mature weed seed being produced. Late maturity, short soybean caused at l east 35% higher pitted morningglory seed weight than the other cultivars. Hemp sesbania in late maturity soybean caused 75% higher seed weight than in the early maturity soybean cultivars. EPOST chlorimuron application decreased weed seed maturity at harv est, reducing the seed weight of pitted morningglory by 23% and hemp sesbania by 46%. Desiccation treatments did not affect either the seed production or the seed weight of either hemp sesbania or pitted morningglory.

Soybean cultivar and EPOST chlorimuron applications both affected seed production and seed weight. The reduction in seed weight is due to decreased seed maturity. Preliminary results indicate germination is lower in the low seed weight, less mature weed s eed. The combination of reduced seed production and decreased germination shows potential for reducing number of weed seed returned to the soil seedbank.

No differences between treatments in weight/100 were observed seed for either species Oxyfluorfen plus sodium chlorate, glyphosate plus sodium chlorate, and glyphosate alone reduced pitted morningglory germination 40 to 43% compared to the untreated. Glyp hosate plus sodium chlorate, paraquat plus sodium chlorate, glyphosate alone, glufosinate, and oxyfluorfen reduced seedling growth of pitted morningglory (germinated from seed collected from treated plants) 29 to 61%. Oxyfluorfen plus sodium chlorate and bromoxynil plus sodium chlorate reduced sicklepod germination by 77 and 70%, respectively. Glyphosate plus sodium chlorate, bromoxynil plus sodium chlorate, oxyfluorfen, and glufosinate reduced seedling growth of sicklepod (germinated from seed of treated plants) 45 to 75%.

Soybeans in Mississippi Mississippi Agricultural and Forestry Experiment Station  Mississippi State University Extension Service Division of Agriculture, Forestry and Veterinary Medicine

For information about this page, contact OAC Webmaster This site is made possible by the Mississippi Soybean Promotion Board and is maintained by the Office of Agricultural Communications at Mississippi State University.

< /body>