Guess the Pest! Weeks 7 & 8 Answer: Wireworm!

David Owens, Extension Entomologist, owensd@udel.edu

Entomologist, owensd@udel.edu

The last Guess the Pest was a bit of a headscratcher in a picture that, if seen in a field, probably would’ve been easier to figure out. Especially if a knife is fixed to the end of a sweep net handle to dig up suspect looking plants.

In several grass and grain crops, wireworm damage is called ‘dead heart’ where the whorl or emerging leaf dies because the wireworm has destroyed the growing point under ground. Larger plants might not be fed on entirely or the wireworm does not hit the growing point. These plants are more likely to show the blotchy yellowing of the leaves. Wireworms are susceptible to seed treatments and to pyrethroids in the furrow. Our northern neighbors in Canada are required to scout fields before a seed treatment can be legally applied. This past spring, I sampled a few fields with bait traps to assess wireworm presence. Bait traps can be time consuming, and the field shouldn’t be disturbed for the 2 weeks the bait is out, a tall order when soil temperatures warm. Cover crops may also interfere with bait attractiveness. Another scouting technique is the compact soil sample method, performed in either fall or spring. This consists of digging an 8 inch x 8 inch x 6 inch deep hole and relating numbers to action thresholds. The other reason I like this method is that a hole has to be dug if the field is being baited, so if there is an economic threshold, odds are you are going to identify it in the process of digging bait holes in addition to when the bait is checked about 2 weeks later.