Wheat Midge Rate - Nozzle Insecticide Trial

Treatment Formulation	Rate Fl. oz/A	Nozzle	Ave. # Larvae per 10 Wheat Heads*	Ave. Yield* Bu/A	Ave. Test Weight* lb/bu
Untreated			12.25 a	37.47 a	58.29 a
Lorsban 4E-SG	8	XR 8001	6.50 ab	38.34 a	58.20 a
Lorsban 4E-SG	16	XR 8001	0.75 b	41.03 a	58.08 a
Lorsban 4E-SG	8	Twin-jet 8002	4.25 b	40.61 a	58.04 a
Lorsban 4E-SG	16	Twin-jet 8002	3.50 b	41.68 a	57.90 a

* Means within the same column are separated by Anova and Fisher's PLSD at a 5% significance level.

The variety Amidon HRSW was planted on May 26, 1999. The high risk planting period (200-600 degree days, base = 40F) for wheat midge infestation was April 30 to May 27, 1999 in the Minot area. So, the May 26 planting date was at the end of the susceptible planting period for wheat midge infestation. Insecticides were applied at late heading (80%) on the evening of July 17, 1999 using a handheld boom sprayer with a XR 8001 or a twin-jet 8002 nozzles (5 nozzles total), 40 PSI, and 18.5 GPA. Night visual observations for adult wheat midge were conducted on two nights by making six observations at 8 different field sites for a total of 48 counts. Night observations for adult orange wheat blossom midge varied - average 1 adult per 3 to 9 wheat heads depending on the field location. Wheat was in the heading to mid-flowering stage during the night observations. The threshold for spraying is 1 wheat midge per 4-5 wheat heads. So, the field was close to the economic threshold level. A total of 40 wheat heads per treatment (10 wheat heads per plot) were randomly collected on August 3,1999. Heads were later examined and counted for wheat midge larvae. Wheat was harvested on September 14, 1999 using a small plot combine.

All insecticides resulted in lower larval counts in wheat heads than the untreated check. Lorsban XR 8001 & 8002 at the 16 fluid oz. rate and lorsban 8002 at the 8 fluid oz. rate had significantly lower larval counts than lorsban 8001 at the 8 fluid oz. rate and the untreated check. There were differences in the yield among treatments, but they were not significant. In general, treatments with lower larval counts had higher yields. For example, the untreated check had a 11% yield loss compared to the highest yield, Lorsban 8002 at the 16 fluid oz. rate. The higher rate of lorsban, 16 fluid oz. rate, had higher yield than the 8 oz. rate of lorsban and the untreated check. At the lower lorsban rate, 8 fluid oz. rate, the twin-jet 8002 nozzle had lower larval counts and higher yields compared to the 8001 nozzle. This suggests that the 8002 nozzle may provide better coverage and protection at the lower rate. There were no significant differences in the average test weights among treatments. The cost to applied lorsban was estimated at $5.66 per acre for the 16 fluid oz. rate and $2.83 per acre for the 8 fluid oz. rate (based on 1999 prices).

We are very grateful to the grower, Travis Zablotney, who let us use his wheat field.


		Department of Entomology, 202 Hultz Hall North Dakota State University, Fargo North Dakota Extension Entomologist: Janet Knodel