Herbicide evaluations for controlling Wild Oats (Avena fatua L.)
in wheat grown in the Sacramento Valley of California.

Jerry Schmierer , Univ. of California Cooperative Extension
and Lorianne Fought, Bayer Corp.

During the 1998-99 growing season, a field trial was established in Colusa County to evaluate the effectiveness of several potential herbicides for control of wild oats, a common weed pest of wheat in the Sacramento Valley. The herbicides were applied when the wheat and wild oats were at the 3-4 leaf, 1-2 tiller stage of growth. Herbicides tested for wild oat control were Bayer MKH6561 and MKH6562, Axiom (FOE5043+ metribuzin), Puma (fenoxaprop+ mefenpyr), Horizon (clodinafop), Achieve (tralkoxydim), and the current standard, Hoelon (diclofop-methyl). Buctril (bromoxynil), MCPA and 2,4-D amine were added to several treatments to test for tank mix compatibility.

The trial was laid out in a randomized complete block design with 4 replications. Individual plots were 10 ft. by 25 ft. with a treated area in each plot of 6.67 ft. by 25 ft. This allowed for an untreated check area in each plot so that weed presence and density could be determined. All herbicide treatments were applied using a CO2 pressurized backpack sprayer. The application rate was 22 gallons per acre. This was accomplished by using four XR8002 flat fan nozzles spaced at 20-inch intervals on the spray boom and operated at 30 psi.

Visual weed control evaluations were made using a 0 to 10 rating scale when the wild oats and wheat were fully headed out. A 0 rating was no weed control, 10 was 100 % weed control and a rating of 8 was determined to be an economic control level that would be satisfactory to a commercial wheat grower. The wild oat population of each plot treated area was estimated by counting heads in a 2-sq. ft. sample area that was repeated 3 times in each plot. The results of the sampled area were extrapolated to the approximate treated area (175-sq. ft.) and reported in the tables. Grain yield was measured by harvesting an area of 5 ft. by 25 ft. in the treated area of each plot using a small plot grain combine. Most all of the herbicide treatments provided above economic control of the wild oats in this trial. Achieve and Axiom (when not in a tank mix combination) did not give significant wild oat control over the untreated check. MKH 6561 at the 0.018 lb. ai/A rate gave the lowest control rating (8.0) of those herbicides that worked, but was within the economic control range. There was no significant difference in yield, even from the untreated control. No wheat phytotoxicity was observed.

WHT98-4