I expect winter moth eggs to start hatching this coming weekend. A few eggs have turned blue and hatched, but more than 95% of eggs are still orange – so not quite ready to hatch. With predicted warmer temperatures starting Friday I think most winter moth eggs will hatch between April 14-22. If you are protecting apple trees, pear trees, and blueberry bushes from winter moth caterpillars, it looks like Friday or Saturday could be a good time to apply an insecticide. Insecticides applied at egg hatch attempt to kill winter moth caterpillars as they hatch from eggs and walk into swollen flower buds.

Hopefully eggs will all hatch by April 22 requiring only one application of insecticide. Another possibility is cooler temperatures return which slows down and spreads out when eggs hatch. We will continue to monitor eggs and let you know.

Winter moth caterpillars are pretty easy to kill, provided they are not inside closed buds. Insecticide choices for caterpillars at egg hatch for fruit growers include, but are not limited to, spinosad, Imidan, Sevin, and Malathion. Spinosad product names are Delegate and Conserve (for commercial growers), Entrust (for organic, commercial growers), and Captain Jack’s Deadbug Brew (for backyard growers). Adding a dormant oil may be useful for the first spray of any of the listed insecticides, provided temperatures stay above freezing for at least 24 hours after application.

Landscape trees don’t need insecticides when eggs are hatching (and probably don’t need any insecticide at all this spring). The best time to spray a landscape tree is when leaves have emerged from buds, exposing winter moth caterpillars. This occurs generally in early May.

Orange eggs on tree bark and arrow showing one egg that has advanced to blue color, indicating it will soon hatch.