Earlier we reported a peak of southern masked chafer adults at The Morton Arboretum the last weekend of June. Another huge number occurred there on July 7, when we normally expect this insect to emerge in northern Illinois. We will have to observe how long these beetles are present before predicting when larvae will have hatched. Last year, we had an extended emergence of these beetles in northern Illinois, with adults emerging late and being present over a six-week period. Because these beetles don't feed as adults, they die about two weeks after emergence.
Degree-day and plant phenology has been running about two weeks ahead of a normal year throughout this growing season at The Morton Arboretum in northeastern Illinois. Along the lakefront, the Chicago Botanic Garden measurements have indicated that they are about two and a half weeks ahead of normal. In central Illinois, we have been about one week ahead of normal.
In central Illinois, the adult annual white grubs appear to be declining. Their appearance is spotty, being heavy in some areas and light in others. This is why it is important for you to observe on your own as well as refer to these reports.