Steve D. Ruhl*, Extension Agriculture and Natural Resources Agent
Jeff Stachler, Extension Associate in Weed Science
Objective: To evaluate the effectiveness of herbicide programs in Roundup Ready soybeans.
Background |
|
| Cooperator:
Nearest Town: Drainage: Major Soil Type: Tillage: Previous Crop: Fertilizer: Soil Test: |
Tom Weiler
Chesterville Tiled Systematically Sloan Conventional Corn None pH - 7.0 P - 23 ppm K - 154 ppm |
| Variety:
Planting Date: Planting Populations: Harvest Date: |
Golden Harvest 352 RR
May 4, 1999 204,000 seeds/ac October 4, 1999 |
The field chosen had tremendous weed pressure from giant ragweed, common lambsquarters, and giant foxtail along with some velvetleaf. Ten different herbicide treatments were replicated four times in a randomized complete block design including an untreated control. Individual plot size was 10 feet wide by 40 feet in length. The preemergence and postemergence treatments were applied on May 8 and June 11, respectively. Treatments were applied with a CO2 pressurized backpack sprayer. At the time of the postemergence application, giant ragweed was six to 10 inches tall, and giant foxtail was four inches tall. Soybeans were at the V4 stage. The treatments were visually evaluated for weed control on August 9.
Table 1. Evaluation of soybean herbicides in Roundup Ready soybeans.
| Weed Control Ratingc (%) | ||||||||
| Herbicide
Treatmentd |
Rate/A | Treatment
Timingd |
Giant Ragweed |
Lambs-quarters | Velvet-leaf | Giant Foxtail |
Herbicide Cost ($/A)a |
Total Costs ($/A)b |
| Canopy Roundup Ultra + AMS |
3 oz. 1 qt. 17#/100 gal |
PRE POST |
100a |
100a |
100a |
100a |
7.50 9.00 0.71 |
37.45 |
| Scepter Roundup Ultra + AMS |
1.4 oz. 1 qt. 17#/100 gal |
PRE POST |
94a |
100a |
100a |
100a |
6.73 9.00 0.71 |
36.68 |
| Roundup Ultra + AMS |
1 qt. 17#/100 gal |
POST | 100a |
100a |
96a |
100a |
9.00 0.71 |
25.95 |
| Dual II Magnum FirstRate + COC |
1.5 pt. 0.3 oz. 1.25% v/v |
PRE POST |
92a |
68cd |
90a |
0c |
17.25 6.88 1.01 |
33.14 |
| Steel Roundup Ultra + AMS |
1.5 pt. 1 qt. 17#/100 gal |
PRE POST |
99a |
100a |
100a |
100a |
7.50 9.00 0.71 |
37.45 |
| Canopy Select + COC + 28% Nitrogen |
6.0 oz. 6.0 oz. 1.0% v/v 4.0% v/v |
PRE POST |
40b |
58d |
48d |
100a |
15.00 8.06 0.84 2.64 |
34.54 |
| Domain Roundup Ultra + AMS |
0.5 lb. 1.5 pt. 17#/100 gal |
PRE POST |
92a |
98a |
90a |
100a |
5.63 6.75 0.71 |
33.33 |
| Python FirstRate + Select + COC + 28% Nitrogen |
1.0 oz. 0.3 oz. 8.0 oz. 1.0% v/v 2.5% v/v |
PRE POST |
87a |
61d |
92a |
100a |
8.31 6.88 10.72 0.84 1.65 |
36.40 |
| Roundup Ultra + AMS |
1.0 pt. 17#/100 gal |
POST | 81a |
92ab |
93a |
100a |
4.50 0.71 |
21.45 |
| Raptor + Cobra + Crop Oil |
5 oz. 10 oz. 1 qt. |
POST | 78a |
81bc |
94a |
66b |
25.50 9.53 1.05 |
40.08 |
| LSD (0.05) | 24.6 | 16.0 | 13.9 | 1.15 | ||||
| CV | 19.6% | 12.9% | 10.6% | 0.9% | ||||
| Treatment means followed by the same letter are not significantly different at P = 0.05.
a Prices used were in-season retail prices. b Application cost of $4.00/acre is included per PRE and per POST treatment. For treatments using Roundup Ultra, the total costs includes a technology fee based on a calculated cost between using seed from Roundup Ready and conventional soybeans with a spread of $9.00 for a 50-pound unit for a total of $12.24/acre. c Preemergence and postemergence treatments applied May 8 and June 11, respectively. Weed control evaluated on August 9. d Abbreviations: COC = crop oil concentrate, AMS = ammonium sulfate, PRE = preemergence, POST = postemergence. |
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The adoption of Roundup Ready soybeans has been rapid. It is reported that 50 to 60 percent of the soybeans planted are now Roundup Ready. However, there are a few weeds that Roundup Ultra doesn't control satisfactorily, and Roundup has no residual weed control. Another concern is having the weather and time needed to apply the Roundup Ultra in a timely fashion to allow for good weed control and no loss of yield due to early or late weed competition.
In this trial the preemergence herbicides did not provide effective weed control due to lack of rainfall. Rainfall received from May 3 - 17 totaled 0.5 inches. Regardless of rate, Roundup Ultra provided good to excellent control of all weeds in this study except giant ragweed at the 1.0 pint rate, although not statistically different. As observed in this study, there is no advantage to a preemergence herbicide application before a postemergence Roundup Ultra application in conventional tillage when the soil is dry at the time of the preemergence application and after the postemergence Roundup Ultra application. The Raptor plus Cobra program might have benefited from the addition of a nitrogen source as an adjuvant, and giant foxtail control was poor due to antagonism of Raptor by Cobra.
The total cost per acre ranged from $21.45 to $40.08 (this includes a technology fee for use of Roundup Ready soybeans) with the Roundup Ultra only treatments being the cheapest. Soybean producers need to weigh the strengths and weaknesses of the many possible herbicide programs to determine which system is most economical for them.
*For additional information, contact:
Ohio State University Extension, Morrow County
871 W. Marion Rd., Suite 102
Mt. Gilead, OH 43338
419-947-1070
ruhl.1@osu.edu