In last week's Bulletin (issue no. 8, May 16, 2003), we provided suggested management strategies for stalk borers and an update on heat unit accumulations for this insect pest. Dispersal of stalk borer larvae (generally fifth to seventh instars) from weed hosts begins when approximately 1,100 heat units (base 41°F) have accumulated since January 1. Heat unit accumulations depicted in Figure 2 indicate that movement of stalk borer larvae from their weed hosts is under way across the southern one-half of Illinois. In extreme southern Illinois, decisions regarding the need for an insecticide treatment should be made in the very near future.
For a complete discussion regarding the management of stalk borers, please take a look at last week's Bulletin (issue no. 8, May 16, 2003).--Mike Gray