August 1, 2019
Issue 7

More on thistle caterpillars.    Thistle caterpillars may be more numerous this year because of spring weather systems that moved more of the moths from the southern US to the Midwest.
There may be a third generation in northwest Iowa - since a third generation occurs in the southern US. This third generation would likely occur over a larger time frame than the first and second generations.
Use an economic threshold of 20% defoliation on soybean plants before insecticide treatment is warranted.
Field Watch. Find the location of specialty crops, organic crops or registered bee hives by checking with Field Watch . You will have to register as an applicator to access this information.
You can then apply filters to find the needed information. Check 'Iowa' under 'Field Watch Map'. Then select 'all' under 'filter growing conditions'.   Select the crop type or beehives under 'filter crop types'.
Soybean gall midge. Check for soybean gall midge damage . Gall midge damage can be found in soybean fields on field edges. Look for wilted plants, dead plants and plants with brittle stems. Galls caused by the gall midge will be located slightly above the soil line.
Green snap in corn. This NDSU article describes some of the yield effects from brittle snap damage in corn. For example, 50% green snap at the V15 stage will reduce yields by 29%. 

Prepared by:
  Paul Kassel- Extension Field Agronomist


Phone:  (712) 262-2264


Serving Clay, Buena Vista, Dickinson, Emmet, Hancock, Kossuth, Palo Alto, Pocahontas, Sac and Winnebago Counties



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