Winter moth caterpillars may still not be very visible, but they are out there. Caterpillars are about half their mature size, so the next couple of weeks is when caterpillars do the most feeding and cause the most damage to shade trees. I expect caterpillars to start dropping to the ground to pupate in about 2 weeks.

Now is a good time to spray most landscape trees to control caterpillars. I prefer using a Bt insecticide such as Dipel because it kills only caterpillars and not other insects. The main problem with Bt insecticides is it lasts for only 3-5 days so additional sprays may be needed. Also, it is not as effective against large caterpillars, so it should be applied soon before caterpillars get much larger. Winter moth caterpillars are pretty easy to kill so most labeled insecticides are effective.

Some trees that are just leafing out have impatient caterpillars, like the pictured caterpillar on a white oak.