April 19, 2018

So what is happening with winter moth eggs, besides driving me crazy? Winter moth eggs have been turning blue and then hatching very, very slowly since around April 4th. In some locations in RI and MA all eggs are still orange (so not ready to hatch) and in other areas 50% of eggs have advanced to the blue color and most of these eggs have hatched. At URI in Kingston and Warwick, RI about 50% of eggs are blue or have already hatched. In Charlestown, 8 miles away and no closer to the coast than URI, only 13% of eggs are blue or hatched. Other areas are similarly confusing.

At all locations, there is not much difference in plant development – forsythia and daffodils are at early bloom, red maples are blooming, McIntosh apple trees are at the green tip bud stage. Since egg hatch has been so staggered and the weather has been so bad, it has been impossible to apply an insecticide and control a large percentage of hatching caterpillars so far. Perhaps an insecticide application within the next couple of days will help control hatching winter moths caterpillars.

The good news is winter moth populations are greatly reduced from previous years so hopefully not spraying at egg hatch will not be a problem. For fruit growers (apples, pears, blueberry growers) perhaps the best strategy is to skip the early spray at egg hatch and concentrate on checking buds in a couple of weeks to see if an insecticide application is needed at that time. A Bt insecticide (DiPel, Biobit, Thuricide, and others) is a good insecticide to use in a couple of weeks because Bt kills only caterpillars. Other insecticide choices include, but aren’t limited to, spinosad (Delegate, Entrust, Captain Jack’s Deadbug Brew), Malathion, or Imidan.

For landscape trees, wait until new leaves emerge and check for little green caterpillars. I don’t anticipate landscape trees needing to be sprayed for winter moth, but if they do, consider spraying a Bt insecticide or spinosad (Conserve).

Past messages can be seen at https://web.uri.edu/ipm/2018-2/