We have received many reports of Japanese beetles and other defoliators munching on soybean over the past few weeks with some reaching economic levels of defoliation. Like a few other insects Japanese beetles are “buffet style” eaters, they have many plants that they can feed on, including corn.
On corn, much of the feeding occurs on silks where they chew the silks back to the ear tip and can interfere with pollination.
Another well-known insect that can feed on silks is the adult corn rootworm (mainly the Western corn rootworm) that should begin emerging soon, if not already.
As tasseling begins and silk emerges, growers will want to make sure that the silk feeding does not reach economic threshold and impact pollination.
Common thresholds are:
- if 5 or more rootworms or 3 or more Japanese beetles are found per ear,
- if silks have been clipped to within 1/2 inch of the ear tip, and
- pollination is less than 50% complete.
As silk clipping is highest along the edges, growers should check at least 100 plants, (10 plants in 10 different areas) to sample the entire field for any signs of silk clipping.