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2002 Annual Report

Economic Injury Level of Winter Wheat Varieties to the Russian Wheat Aphid

M.D. Koch

PROBLEM: Russian wheat aphid Diuraphis noxia (Mordvilko) resistant hard red winter wheat varieties have been successfully introduced throughout the central Great Plains region. New varieties need to be tested before actual resistance in the field is known.

APPROACH: The experiment for 2002 compared a Russian wheat aphid (RWA) susceptible variety with three resistant varieties. Akron was the susceptible variety while Ankor, Halt and Stanton were the resistant. Experimental design was a split plot where infestation levels were grouped together for each replication. Eight replicates and three infestation levels were used. The infestation levels were 0x, 1x and 10x RWA. Infestation level 0x had a seed treatment of 8.3 ounces per hundred pounds of imidacloprid (Gaucho). They also were sprayed with 0.50 lb (AI) per acre of chlorpyrifos (Lorsban 4E-SG) on 14 May 2002 to ensure no aphid damage. Each plot was six foot by six foot. They were planted 22 September 2001 with a reduced tillage cone planter. Akron wheat was planted in all borders around the plots. Each replication was surrounded by a six foot border.

All plots had two subplots of paired one meter rows. These rows were used for sampling. One row was used to destructively sample by growth stage (stem elongation and boot) for determination of actual infestation levels. The other row was for yield analysis. Each paired row was artificially infested using the bazooka method on 10 April 2002. Total RWA on each of the 1x rows was calibrated to be 50 (49.4) and the 10x rate with 500 (486.8) aphids.

Destructive sampling of one half meter began on 02 May 2002 (Zadoks growth stage 30-32). The susceptible variety was showing symptoms of RWA damage. Total tiller counts were taken from each plot. Then counts were taken for the following: asymptomatic and no RWA, asymptomatic with RWA, symptomatic and no RWA, and symptomatic with RWA. After counting the tillers, samples were placed in Berlese funnels for 24 hours to extract the aphids from the plants. The RWA were then counted for each sample. The same procedure as above was followed exactly for the second half of the row meter. This began on 29 May 2002 (Zadoks 47-57) with high aphid pressure. Growth stage variability was largely due to drought conditions experienced throughout the growing season.

Harvesting was done on 01 July 2002 using scissors to cut the heads off of each row meter opposite the destructively sampled row. Total head counts were taken during harvest. Small paper grocery bags were used to store the heads until thrashing began 15 July. An Agriculex SPT-1 thrashing machine was used to separate grain from heads. Each sample was cleaned using a small Rapsco aspirator. Total seed weight was taken and the samples placed in a model 850-2 Old Mill Company seed counter. One thousand seeds were counted and weighed to determine test weight.

RESULTS: This experiment was repeated throughout eastern Colorado. The results in the table show yield comparisons at the Akron, Colorado site. For more information contact Mike Koch at the Central Great Plains Research Station, Akron, Colorado or Dr. Frank B. Peairs at the Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, Colorado. Results will be published in the Colorado Field Crop Insect Management Research and Demonstration Trials Technical Bulletin.

Means in the same column followed by the same letter(s) are not statistically defferent, SNK (%=0.10)