Timing Insecticide-Fungicide Trial 1999

Treatment Formulation	Rate Fl. oz/A	Crop Stage	Ave. # Larvae per 10 Wheat Heads*	% Scab Severity	% Leaf Disease Severity	Ave. Yield* Bu/A	Ave. Test Weight* lb/bu
Untreated			24.25 a	3 a	23 a	35.67 a	58.58 a
Lorsban 4E-SG	16	Late heading	4.75 b	4 a	21 a	38.82 a	58.36 a
Lorsban 4E-SG + Folicur 3.6F	16 + 4	Late heading	8.75 b	4 a	10 b	41.67b	58.80 a
Folicur 3.6F	4	Late heading	38.25 c	5 a	9 b	39.27 a	59.08 a
Lorsban 4E-SG	16	Early flowering	10.25 b	5 a	17 a	40.23 a	59.35 b
Lorsban 4E-SG + Folicur 3.6F	16 + 4	Early flowering	4.50 b	1 a	6 b	42.18 b	58.96 a
Folicur 3.6F	4	Early flowering	23.75 a	2 a	14 a	39.71 a	58.92 a
Lorsban 4E-SG	16	Mid flowering	8.25 b	5 a	19 a	39.76 a	58.87 a
Lorsban 4E-SG + Folicur 3.6F	16 + 4	Mid flowering	10.50 b	2 a	19 a	43.16 b	58.67 a
Folicur 3.6F	4	Mid flowering	31.00 a	1 a	17 a	39.88 a	58.80 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 = 40^BF) 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-fungicides were applied at late heading (80%) on July 17, 1999 for the first timing, at early flowering on July 19, 1999 for the middle timing, and at mid-flowering (50%) on July 21, 1999 for the late timing using a handheld boom sprayer with XR 8001 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 averaged 1 adult per 4 and 3 wheat heads on the nights of July 18 and 21, 1999, respectively. 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 at 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. Ten whole wheat plants were also collected per treatment plot on August 9, 1999 to determine the percent incidence and severity of scab and leaf diseases (tan spot and Septoria). Wheat kernels from each treatment were sent to Fargo for DON (vomitoxin) tests. Wheat was harvested on September 14, 1999 using a small plot combine.

All insecticides and insecticide-fungicide treatments resulted in significantly lower larval counts in wheat heads than the untreated check and the fungicide only treatments. The late heading and early flowering applications had the lower larval counts compared to the mid flowering application, but there was no significant differences among timings. Folicur has no negative affects on lorsban’s efficacy against wheat midge. For wheat scab (head blight), the incidence in the untreated check was 40% and averaged about 23% in the fungicide treated plots. However, there was no significant differences among treatments for percent severity of scab, probably due to the low level of scab pressure in the Minot area during 1999. DON levels (vomitoxin) were also very low (averaged # 0.5 ppm) in all treatments. In contrast, the leaf disease pressures were severe with a 100% incidence. The late heading and early flowering timings for fungicide applications had significantly lower percent severity of leaf diseases, except for the fungicide alone application during early flowering (lower but not significant). No significant differences were observed during mid-flowering, which indicates that this timing was too late for effective leaf disease control. There were significant differences in the yield among the treatments. Treatments with both insecticide+fungicides had significantly higher yields than the other treatments regardless of the timing. This suggests that the pressures from both wheat midge and diseases reduced the yield. The untreated check had a 18% yield loss or 7.5 fewer bushels per A compared to the highest yield, lorsban + folicur at mid-flowering. The estimated costs to applied the insecticide, lorsban, is about $5.66 per A and the fungicide, folicur, is about $9.14 per A; which would make lorsban+folicur about $14.80 per A (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