We may see winter moth eggs hatching at the end of this week. Using The Weather Channel growing degree days (GDD)calculator and their weather predictions, it looks like we will reach 114 GDD, base 40 at the end of this week. This is assuming 114 GDD is a good target number for winter moth eggs hatching and assuming weather predictions are accurate. Here are when some towns reach 114 GDD or predicted to exceed 114 GDD the next day.
4/16/15 Bristol 108 GDD 02809
4/16/15 Cumberland 107 GDD 02864
4/16/15 Greenville 107 GDD 02828
4/18/15 Kingston 112 GDD 02881
4/20/15 Little Compton 113 GDD 02837
4/20/15 Middletown 113 GDD 02842
4/17/15 North Kingstown 114 GDD 02852
4/19/15 Westerly 113 GDD 02891
You can check look up GDD at your zipcode at:
Enter your zipcode
Select base temperature 40
Select start date – use March 1st
Select end date – use yesterday’s date to see what GDD we are up to, or put in a future date to see what
Click on Calculate
We will continue to monitor for eggs turning from orange to blue and then hatching at 5 locations. Eggs turn blue a couple of days before hatching. No monitored eggs have turned blue yet.
If you are planning to spray oil to help control winter moth eggs, this is a good week to apply oil since we are close to eggs hatching and night time temperatures are predicted to stay above freezing. Dormant oil applications can suffocate eggs before they hatch. Dormant oil can also be mixed with most insecticides.
I still think it’s a good idea to wait to spray an insecticide until eggs begin to turn blue. Most insecticides will control winter moth caterpillars if applied right before eggs hatch and caterpillars move inside buds. Bt insecticides (Bacillis thuringiensis) such as Dipel will not control winter moth caterpillars when they first hatch but is effective once buds open.
If you look closely at this picture you can see small, orange eggs among the green lichen. These eggs are congregated like this because I set up tree wraps in the fall which encouraged female winter moths to lay eggs under the band.