August 15, 2019
Issue 8

Third generation thistle caterpillars. There is likely to be a third generation of Thistle caterpillars . There are current reports of thistle caterpillar larvae in southern and central Iowa.
Continue to check fields for defoliation from other insects as well and use an economic threshold of 20% defoliation .
Soybean aphids. The yield benefit for treatment for aphids declines after the late R5 stage/early R6 stage. The R5 stage is where the soybean seed is 1/8 inch long at one of the top four nodes and is 15 days in duration. The R6 stage is where the soybean seed completely fills the pod at one of the top four nodes.
Thresholds are less clear at the late R5 stage/early R6 . Info from the University of Minnesota suggests that treatment for aphids at the early R6 stage can be beneficial if dry soil conditions are prevalent.
US Drought Monitor . The first level of drought - referred to as abnormally dry - has worked its way into the area. Check the Drought Monitor for the latest soil moisture conditions.
Corn root ratings. Check corn fields for damage from corn rootworm feeding. The late spring and cool soil temperatures delayed the egg hatch of corn rootworms. Some early June planted corn has shown damage from rootworm feeding. Dig and wash roots to evaluate damage. Assess the amount of damage use this interactive website .

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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