April 4th Winter Moth Update

We’ve been blessed with cool weather – at least that’s the way I look at the last few weeks with regards to slowing down the growing season and winter moth egg hatch. I’ve heard from many people monitoring eggs and I monitor hundreds of eggs, and nearly all eggs are still orange – so not hatching yet. A few eggs have turned from orange to blue, but I think these eggs are outliers, and not of concern. For those of you intending to apply insecticides when eggs start hatching, we want to time the application when about 10% of eggs have turned blue and start hatching. Generally it takes only a day or two for eggs to hatch once turned blue. The average date for winter moth egg hatch is April 10.

Night time temperatures for the next week are forecasted to be too cold to apply dormant oil. Temperature should remain above freezing for at least 24 hours following an oil application or you risk damaging buds.

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 remain above freezing.

Training workshop for egg monitors in spring 2016.
Photo Tawny Simisky, UMass