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ProCrop |
Orange Wheat Blossom Midge Rate-Nozzle Insecticide Trial
1999 -
HRSW Benson County (Minnewaukan)
The variety Russ HRSW was planted on May 10, 1999. The high risk planting period (200-600 degree days, base = 40BF) for wheat midge infestation was May 2 to May 30, 1999 in the Baker area. So, the May 10 planting date was in the middle of the susceptible planting period for wheat midge infestation. Lorsban insecticide was applied at early heading (30%) on July 11, 1999; and at late heading (90%) on July 14, 1999. All treatments were applied with a backpack sprayer using a double swivel adapter containing XR 8001 or a turbo 8002 nozzles (5 nozzles total), nozzles angled 30� from horizontal and directed forward and backwards to the direction of travel, 40 PSI, and 18.5 GPA. Table 1 includes application information. The levels of Orange Wheat Blossom Midge were observed at 1 adult per 6 heads at the 90% headed stage. The threshold for spraying is 1 wheat midge per 4-5 wheat heads. So, the field was slightly below the economic threshold level. Ten heads per plot were sampled August 4, 1999. It appeared that some midge larvae may had left the heads due to a light rainfall the day before.
Results of the wheat midge counts are summarized in Table 2. There were no significant differences in the number of wheat midge larvae per head between treatments applied at the early 30% heading stage. This application timing was too early for effective control of wheat midge. In contrast, all insecticides applied at the late 90% heading stage resulted in significantly lower larval counts in wheat heads than the untreated check. Although there were no significant differences between insecticide rates, the half rate (8 fl. oz./A) of Lorsban had slightly higher larval counts compared to the full rate (16 fl. oz./A). There was also no significant difference between the type of nozzles. This indicates that both nozzles provided adequate coverage and protection at both rates. 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, Howard Schmidt, who let us use his wheat field. This work was supported by SBARE, North Dakota Wheat Commission, and Dow AgroSciences.
Table 1. Conditions during spray applications.
|
Application Date |
Relative Humidity |
Temperature |
Sky Conditions |
Wheat Growth Stage |
Wind Direction and Speed mph |
Time |
|
7-11 |
70% |
74� F |
Sunny |
30% headed |
East 0-5 |
8:30 pm |
|
7-14 |
75% |
75� F |
Sunny |
90% headed |
East 0-3 |
9:00 pm |
Table 2.
|
Treatment |
Rate |
Nozzle |
30% |
90% |
|
Ave. # Larvae per 10 Wheat Heads* |
||||
|
Untreated |
6.3 |
9.0 |
||
|
Untreated field samples (outside plots) |
4.0 |
-- |
||
|
Lorsban 4E-SG |
8 |
XR 8001 |
3.5 |
1.3 |
|
Lorsban 4E-SG |
16 |
XR 8001 |
3.5 |
0.0 |
|
Lorsban 4E-SG |
8 |
Turbo 8002 |
8.0 |
2.5 |
|
Lorsban 4E-SG |
16 |
Turbo 8002 |
4.8 |
0.8 |
|
MEAN |
5.0 |
2.7 |
||
|
C.V. % |
75.9 |
70.6 |
||
|
LSD 5% |
NS |
2.9 |
||
* Means within the same column are separated by Anova and Fisher�s PLSD at a 5% significance level.
Janet Knodle1 and Terry Gregoire2
1 North Central Research Extension Center, NDSU, Minot, ND
2 NDSU Extension, Devils Lake, ND
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