Watch for Japanese beetle on “Silking” Corn.

Doug Johnson, Extension Entomologist



Japanese beetles feeding on corn silks.

 Japanese beetles have been emerging over the last couple of weeks. With the general rainfall we had last Monday (6/11/12) this emergence is likely to quicken. While this insect will feed on corn leaves, its’ only real importance is when feeding on emerging silks. This silk feeding can interfere with pollination resulting in incomplete kernel set. Figure 1.


These insects are metallic green beetles about ½ “ long. They have a row of white tufts on either side of the body below the bronze wing covers. The beetles will congregate (sometimes in very large numbers) on ear tips and feed on the silks, thus preventing proper pollination.

Normally, this insect is not a major pest of corn. However, in this year because of the mild winter and very warm spring the pest is emerging at an earlier date. Also, because of the dry soil conditions in the western part of the state, the emergence which is normally spread out in time, may occur over a much shorter period producing an unusually large number of beetles seemingly all at once.

Scout for this insect by examining several individual groups of 20 consecutive ears. Determine if the silks have been clipped to within 1/2” in length. Additionally, count the number of beetles per ear and average these numbers for the twenty ears per sample, then average all the samples taken in the field. Treatment may be necessary if silks have been clipped to ½” and there are three or more beetles per ear.

If pesticide application becomes necessary, pesticides useful for control of Japanese beetle can be found in ENT-16, Insecticide Recommendations for Corn-2012, which may be obtained from your County Extension Office or on line at:

http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html

Photo: ©D. Johnson, Univ. KY