Reports received: 25 of 34 monitoring sites submitted data this week.

Trap catches this week:

• European corn borer (ECB-E): reported at 2 sites
• European corn borer (ECB-Z): reported at 7 sites
• Corn earworm (CEW): reported at 15 sites, 13 high enough to be on a 4,5, or 6 day spray schedule
• Fall armyworm (FAW): reported at 2 sites
• Western bean cutworm (WBC): reported at 1 sites

Even though ECB trap catch numbers remain low, feeding damage has been observed in the field.

Eggs take approximately 100 base 50 degree days to hatch. Egg masses will change from white to cream to black as they age. When they appear black they are in the “black head” stage and will most likely hatch with 24 hours (see photo).

For ECB feeding in the whorl it is important to time spray applications to target the larvae when they leave the tassel but before they bore into the plant.

Larvae feeding in the whorl are protected from insecticide applications and mortality will not be as high as at tassel emergence, when larvae feeding in the emerging tassel are exposed to the spray.  Larvae will leave the tassel as it opens up and no longer provides a moist, protected feeding environment, and move down the plant looking for protected places to feed.  Insecticide applications need to be timed to kill larvae before they bore into a new feeding location where again they will be protected from sprays.  In fields with very uneven development, two applications may be necessary, one when approximately 25-50% of the tassels have emerged, and again after 75-100% of the tassels have emerged, if the field is still over threshold.

J.W. Apple, Department of Entomology, University of Wisconsin-Madison

Table showing trap catch for 6.24.25 – 7.1.25.

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