David Owens, Extension Entomologist, owensd@udel.edu
Congratulations to Joe Streett for correctly identifying last week’s Guess the Pest challenge as cabbage white, also known as the imported cabbageworm. Joe won a heavy duty sweep net for catching the butterflies and will be entered for the end of season raffle along with all others who submitted correct answers. This is one of the early harbingers of spring. I saw my first April 1 and it is now the most common butterfly out. It is a Brassica specialist. Females lay eggs on wild mustard, brassica cover crops like turnip or radish, and cultivated brassicas such as broccoli and cabbage which are being transplanted now. Larvae are green, about an inch long, and fuzzy. They are easiest to find when ‘hiding’ on the leaf’s upper midrib. Pre heading, brassicas can tolerate a good deal of defoliation (30% infested plants), but once heading initiates, thresholds for this and other defoliating worms drop to 5%.
