Twenty sites reporting this week. Eleven sites reporting European corn borer (ECB)-E. One site, Seneca Castle, had the high count with 159 moths.  ECB-Z was reported from six sites. Corn earworm (CEW) was caught at six sites with four sites high enough to require a 6 or 5 day spray interval (see spray table at bottom of post). Thirteen sites reporting Fall armyworm (FAW) and eighteen sites reporting Western bean cutworm (WBC). Eden had the high count for both FAW and WBC with 81 and 289 moths respectively.

Degree day accumulations for sweet corn trap sites range from 1082-1485 (modified base 50F) with an average of 1333. The second generation ECB-E are predicted to fly at 1400 degree days (see chart below). WBC emergence is predicted to be at 50% when degree day accumulations reach 1422 (chart below). We are currently well within the range for both of these to occur at several of the sites. It is also recommended that scouting for WBC begins when cumulative trap catches reach 100 moths, however egg masses have been found when trap catches were still in the single digits. WBC threshold for fresh market sweet corn is only 1%. It is important to scout late whorl and early tassel-emergence fields as these are most at risk. After hatching larvae will spend a few days feeding on the tassel before moving down to the ear.

J.W. Apple, Department of Entomology, University of Wisconsin-Madison

Percent WBC moth emergence, data from University of Nebraska