In 2017, ISU is reporting black cutworm (BCW) peak flights by county and providing degree day resources for more personalized cutting prediction dates using actual accrued degree days for a specific location. We first reported on BCW peak flights in the ICM News in early May. As an update to that article, the reported peak flights in Iowa from April 1 thus far are below (Table 1.) The counties with the earliest peak flights (Marshall, Muscatine, and Tama) have already reached the scouting threshold. Woodbury county will reach the scouting threshold within the next few days. We continue to see low numbers of moths in traps in Iowa.
Table 1. Reported black cutworm peak flight dates from April 1 through May 23, 2017 in Iowa.
|County||Peak flight date|
Next, use this degree day calculator to determine when 300 degree days is approaching for your area based on any nearby peak BCW flights. Make sure the “Iowa Long Term Climate Sites” is selected for Available State and “Growing Degree Days (base=50)” for Select Parameter. Then input the peak flight date for the first set of dates and today’s date for the second set before clicking on the “Make Plot” button. The resulting map will show you how many degree days have elapsed since the peak flight.
As the resulting numbers get closer to 300, keep a close eye on the map as you will want to be scouting a few days before the actual 300 scouting threshold in case your fields have experienced slightly different temperatures than the reporting stations on the map. Iowa counties near the border of Illinois should probably pay attention to IL cutting dates, which are posted at the University of Illinois’s The Bulletin: http://bulletin.ipm.illinois.edu/?p=3865.
It is important to remember that just because a peak flight has not been reported for your area, it doesn’t mean that fields won’t be injured by BCW larvae. Conversely, high trap captures don’t necessarily translate to high injury potential.
For information on Scouting, Identification, and Thresholds, see this recent ICM News article.