Memorial Day Weekend, and Winter Moth Caterpillars are well into their “free feeder” stage. They are highly mobile now, as you may have noticed them dripping down out of larger trees on silken threads. This time can be especially frustrating for arborists looking to manage these pest and prevent them from mauling the trees and shrubs we take care of because they will feed on anything they hit on the way down to the ground. So even when we’ve gotten all our plants protected in a timely manner, caterpillars from neighboring untreated plants often come blowing in and start feeding all over again. Only now they are in their fifth instar, are huge, and can devour a lot of foliage in a single day. This is one of the main reasons we need 2 spray visits to manage them well.
My observations this year are that the really dense and truly destructive population concentrations are highly localized and very plant specific. I am seeing many situations where several trees have relatively light damage but are surrounded by fully defoliated plants all within a few hundred feet from each other–what’s the rhyme or reason? I don’t know, but vigor definitely plays a role. They are very focused on all the ornamental malus and prunus, they’ve always liked Norway Maples (and they can have them), and I’ve also seen a predilection for Green Ash this year. I look forward to the time when these guys are fully in the rear view mirror.