Twenty-seven sites reported this week. European corn borer (ECB)-E was trapped at seven sites and ECB-Z was trapped at nine sites. Fifteen sites reported corn earworm (CEW) with ten sites high enough to be on a 4, 5, or 6 day spray schedule (see chart below). Fall armyworm (FAW) was trapped at two sites and Western Bean cutworm (WBC) was trapped at four sites this week.

Even though ECB trap catch numbers remain low, feeding damage has been observed in the field. If corn is in the tassel emergence stage the threshold is 15%. The threshold for silking corn drops to 5% infested plants. If the corn field is silking, scout for egg masses and larvae within the ear zone. The ear zone is the area between the two leaves above the top ear and one leaf below the bottom ear. ECB egg masses are usually located on the underside of the leaf along the midrib. The egg mass consists of 10-35 flattened eggs that overlap like fish scales. 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).

ECB egg mass – white stage
(photo from UNL Department of Entomology).

ECB egg mass “black head” stage
(photo from UNL Department of Entomology).

Many sites reported CEW this week. CEW is difficult to scout for but pheromone trap catches may be used to time sprays according to the table below. Add one day to the recommended spray interval if daily maximum temperatures are less than 80° F for the previous 2-3 days.