Ohio State University Research/Extension Bulletin

Agronomic Crops Team On-Farm Research Projects 1997

Special Circular 160-98


SOYBEAN

1997 Reduced Rates of Herbicides in Roundup-Ready Soybeans

Objective

Determine if reduced rates of herbicides can provide adequate weed control and show no yield loss in no-tillage soybean utilizing pre-emergence and post-emergence herbicide applications.

Cooperator: Jim Patton
County of Site: Logan
Nearest Town: Belle Center
Major Soil Type: Paulding Clay
Drainage (List Type): N/A
Irrigation: No
Tillage: None
Previous Crop: Soybean
Soil Test: pH N/A
P N/A
K N/A
Fertilizer Applied: N/A
Herbicide Program: Listed in table
Plant Population: 210,000 seeds per acre
Plant Population @Harvest: N/A
Variety: Asgrow 3301 (Roundup-Ready)
Planting Date: May 14, 1997
Harvest Date: October 15, 1997

Materials and Methods

The plot size for this study was 20 feet wide and 300 feet in length. Each treatment was replicated three times. 2,4-D ester at 1.0 pt/A plus Prime Oil (COC) was added to treatments 1-7 and applied alone to treatment 8 to control existing weeds 29 days prior to planting. The 1X Canopy rate was 6.0 oz/A and 1X Squadron rate was 3.0 pt/A. The post-emergence application of Roundup Ultra at 1X rate was 1.5 pt/A and applied based upon the broadleaf weed height listed in the table. Annual grass height was 1.25" for 1/4X rate, 3.5" for 1/2X rate, and 7.0" for 1X rate.

Results

application, LSD = least significant difference, NS = no significant difference.
Treatment
and Rate1
Treatment Timing1 Weed Control on August 4, 19971
(--- % ---)
Soybean
Yield1
(bu/A)
Treatment
Cost2
($/A)
Height
(inch)
DAP An. Gr. C. Rag.
1. Canopy (EPP) 1/2X- 29
(POST) 1/4X< 133871005323.78
2. Canopy (EPP) 1/2X- 29
(POST) 1/2X< 240981005226.00
3. Canopy (EPP) 1/2X- 29
(POST) 1X3-5491001005330.44
4. Squadron (EPP) 1/2X- 29
(POST) 1/4X< 13385925328.72
5. Squadron (EPP) 1/2X- 29
(POST) 1/2X< 24097965330.94
6. Squadron (EPP) 1/2X- 29
(POST) 1X3-54998995335.38
7. Squadron (EPP) 1X- 2977555229.16
8. Roundup (POST) 1X3-542981005223.21
LSD (0.05%) 6.57NS
1 Abbreviations: Height = broadleaf weed height,
DAP = days after planting, An. Gr. = annual grass (giant foxtail,
yellow foxtail, and fall panicum), C. Rag. = common ragweed, bu/A =
bushels per acre, EPP = early pre-plant application, POST = post-emergence
2 Treatment cost = cost of all herbicides and additives
(including burndown), application cost at $2.00/A/application, and
Roundup-Ready technology fee of $7.50/A.

Summary and Notes

The weed pressure in this study was light. The reduced annual grass control in treatments 1 and 4 is due to the lack of rapid soybean canopy closure after application, because the soybeans were only at the second trifoliate at application. Despite the lower weed control in treatments 1, 4, and 7, there was no significant reduction in yield.

For additional information, contact:

Jeff Stachler and Dr. Mark Loux
Kottman Hall
The Ohio State University
2021 Coffey Road
Columbus, OH 43210
614-292-1393 or 614-292-9081
stachler.1@osu.edu or loux.1@osu.edu


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