Agronomic Crops Team On-Farm Research Projects 1999

Special Circular 176-00

Evaluation of Corn Herbicides on Roundup Ready Corn

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 Corn.

Nine different herbicide treatments and an untreated control were replicated four times in a randomized complete block design. Individual plot size was 10 feet wide x 40 feet in length. The preemergence and postemergence applications were applied on May 8 and June 8, respectively. Treatments were applied with a CO2 pressurized backpack sprayer. The plots were visually evaluated for control of annual grasses, common lambsquarters, and giant ragweed on August 9. The weed pressure was moderate to heavy at this site. The weed control ratings for each treatment were averaged across the four replications.

Results

Weed control results are listed in Table 1.

Summary and Notes

Preemergence treatments received little rainfall during May. Rainfall received from May 3 - 17 totaled 0.5 inch. This was not enough rainfall to properly activate the preemergence treatments, thus causing them to provide ineffective weed control. All postemergence treatments provided excellent weed control, except Distinct for annual grass control. The preemergence herbicides that were followed by Roundup Ultra provided little benefit to weed control achieved under this year's conditions. With the dry weather after the total postemergence application, these treatments provided excellent control that is not always expected when using a non-residual herbicide in corn. The total postemergence Roundup Ultra treatments had the lowest herbicide cost. However, many producers are concerned about the additional cost of the technology fee associated with Roundup Ready corn.

Table 1. Evaluation of herbicide programs for use in Roundup Ready Corn

			Weed Control Ratingc (%)
Herbicide Treatmentbd	Rate/A	Treatment Typed	Annual Grasses	Lambs-quarters	Giant Ragweed	Herbicide Cost ($/A)	Total Costsa ($/A)
Roundup Ultra + AMS	1 qt 17#100 gal	POST	100a	99a	98a	9.55 0.71	14.26
Balance + Aatrex Roundup Ultra + AMS	1 oz. 0.75 lb. 1.5 pt. 17#/100 gal	PRE   POST	100a	98a	98a	7.99 2.18 7.16 0.71	26.04
Balance + Aatrex + Princep	2 oz. 1.5 lb 1.0 lb	PRE	84b	88ab	69b	15.98 4.35 3.93	28.26
Balance + Aatrex Distinct + Surfactant + 28% Nitrogen	1.5 oz 0.75 lb 6.0 oz 0.25% v/v 1.25% v/v	PRE   POST	89b	97a	100a	11.98 2.18 13.12 0.45 0.17	31.90
Balance	2.5 oz	PRE	84b	85ab	76ab	19.98	23.98
Harness Xtra	2.4 qt	PRE	92ab	74b	59b	24.73	28.73
Axiom + Aatrex	18 oz 1.5 lb	PRE	85b	80b	59b	18.60 4.35	26.95
Epic + Aatrex	12 oz 1.5 lb	PRE	88b	88ab	71b	24.00 4.35	32.35
Balance Roundup Ultra + AMS	1.0 oz 1.5 pt 17#/100 gal	PRE POST	99a	100a	98a	7.99 7.16 0.71	19.86
LSD (0.05)			9.3	16.4	24.2
CV			7.1%	12.5%	20.5%
Treatment means followed by the same letter are not significantly different at P = 0.05. a Application cost of $4.00/acre is included per treatment. Prices used were in-season retail prices. b Preemergence treatments were applied on May 8 and received little rainfall during May. Rainfall received was: May 3 - 17 = .5, May 18 - 31 = 1.95. The postemergence treatments were made on June 8. G. Ragweed was 6-10 inches tall and annual grasses (mostly giant foxtail, but some barnyardgrass and fall panicum) were 4 inches. Corn was in the 2-3 collar stage. c Weed control ratings equal percent of weeds controlled relative to untreated check. It is the average of four replications. d Abbreviations: AMS = ammonium sulfate, PRE = preemergence, POST = postemergence.

*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