Doug Johnson, Extension Entomologist, University of Kentucky.
Capture of Armyworm (AW) and Black cutworm (BCW) moths at
the UK-REC in Princeton have dropped back to near normal levels. This is to be expected and indicates the end of the migrator flight into Kentucky from further south. For both species we now wait and monitor for the appearance of the caterpillars.
Using our Biofix date of April 9th for both pests and another week of real weather data, our calculator predicts the appearance of armyworm caterpillars on or about 01 May and the appearance of 4th instar BCW caterpillars at about 10 May. It is important to remember that for AW we are predicting the very first instar (tiny caterpillars) while for Black cutworm we are predicting the 4th instar (larger caterpillars) that are able to cut corn plants. One may see 1st – 3rd instar larvae chewing on plant leaves in the weeks before. This is an indicator that the pest is present but not yet at the danger point. You may wish to refer to the earlier articles for economic thresholds for treatment.
Remember these predictions are based on data from Princeton (Caldwell Co.) KY. Other locations will vary depending upon the differences in temperature. Additionally, it appears that in this season, each week we run the model with real temperatures the arrival dates move earlier, indicating that it is getting warmer with each passing week. This projection is only telling you when it is the best time to look for the pests. It is possible that neither, both, or one or the other of these insects may appear in a given field.