Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
As field corn begins pollinating, watch for silk clipping from Japanese beetles. This past week, I have seen an increase of Japanese beetles in soybeans. What does this have to do with corn? Well, Japanese beetles also damage corn by clipping silks prior to and during pollination. With the earliest fields starting to silk, watch for Japanese beetle populations moving into corn and clipping silks.
Sample 10 plants in 10 locations throughout the field to determine the stage of pollination, number of beetles per ear, and the percentage of plants with silks clipped to less than ½ inch. As a general rule, treatment may be necessary if silks are clipped to less than ½ inch and less than 50% of the plants have been pollinated and 3 or more Japanese beetles per ear are actively feeding (information from Purdue University, https://extension.entm.purdue.edu/fieldcropsipm/insects/corn-japanese-beetles.php). Japanese beetle populations will typically be most concentrated on field edges so make sure you are also scouting the interior portions of the field when determining if a spray is necessary.
How can you tell when an ear has been pollinated?
Pollen shed for an individual tassel usually takes 2-7 days and 1-2 weeks for an entire field. So how can you determine when you have reached 50% pollination?
Here is an informative Youtube video by Dr. Bob Nielsen demonstrating how to perform an ear shake test to determine corn pollination progress: https://www.youtube.com/watch?v=K7DiwD4N0T0&feature=youtu.be
Please refer to our Field Corn Insecticide Recommendations if a control measure is necessary: https://cdn.extension.udel.edu/wp-content/uploads/2012/05/13055805/Insect-Management-In-Field-Corn-final-20171.pdf