(Kacey Birchmier) – Japanese beetles are back. Illinois reports indicate Japanese beetle populations are very high in some locations, says Kelly Estes, state survey coordinator for the Illinois Cooperative Agricultural Pest Survey Program, in the University of Illinois Bulletin.

“With corn starting to tassel and getting close to tassel, it’s important to remember, even though densities may appear to be extremely high, the average density of beetles across the field may be below levels of economic concern,” says Estes.


An insecticidal treatment should be considered during silking if:

  • There are 3 or more beetles per ear.
  • Silks have been clipped to less than ½ inch.
  • Pollination is less than 50% complete.

When it’s time to scout, remember there are usually clusters of Japanese beetles near field edges. If those are the only locations sampled, it will skew the numbers, warns Estes.

“It’s important to scout flowering soybean fields for the presence of Japanese beetles,” says Estes. “Insecticidal treatments should be considered when defoliation reaches 30% before bloom and 20% between bloom and pod fill.”

Get out there and scout during #grow17 for this pest! Below are images of Japanese beetles on crops across the Midwest.



(Mycogen Seeds) – Pollination often takes place over a week’s time or longer, and corn plants are most vulnerable to pollination stressors during the two weeks of pollen shed. Extreme heat and drought stress lead the list of factors that hinder effective pollination.

This is especially true when daytime temperatures exceed 95 F with low relative humidity and plants are experiencing drought stress during the critical pollination period. The greater the number of days the plants experience the described conditions, the greater the potential yield impact. In addition, temperatures above 100 F can seriously hinder and even kill pollination.


Most weather-related pollinator stress is caused by hot temperatures combined with a lack of rainfall. However, damage resulting from hailstorms during the tasseling stage can be equally harmful, further reducing the pollen source.

“During pollen shed, without any cooling at night, farmers will see the most issues,” says Jason Welker, Mycogen commercial agronomist for western Nebraska. “Unfortunately, we can’t control Mother Nature, but understanding how conditions can impact pollination can help us to determine potential yield loss.”

While growers are powerless against the forces of Mother Nature, there are steps to take to mitigate the effects of both insect feeding damage and environmental conditions. For example, applying irrigation during drought stress can help.

Managing pest populations is one way corn growers can improve pollination potential. Feeding by corn rootworm beetles and Japanese beetles can damage cornsilks, potentially decreasing the silks available for pollination.

Drought or heat stress during pollination can also result in zipper ears, or ears with missing kernel rows. Ears affected by zippering have kernels that developed poorly or more slowly than other kernels or have ovules that aborted shortly after pollination. Also, scout for silk-feeding beetles during pollination, and treat when population thresholds are reached.

“Understanding how heat and other environmental factors impact yield can help growers plan,” Welker adds. “If you know you’re a in drought- or heat-stressed geography, consider lower populations, a full-flexed ear type and even a stress-tolerant hybrid.”

Additional resources: