So, winter moth caterpillars are finished or nearly finished for the year, but we are not finished with caterpillars. I’ve been frantically trying to answer emails and phone calls, but what I need to do is alert more people about what is going on in our caterpillar-infested state. Please look at attached pictures to help you identify caterpillars.

Winter moth caterpillars were not as bad as expected – though some locations had large populations and blueberry and apple trees suffered a lot of damage. I do not know the status of the parasitic fly, Cyzenis albicans. I collected winter moth caterpillars at all 7 RI sites where the fly was released in previous years to check for parasitism. Results about parasitism will not be available for several months.

Gypsy moth caterpillars are about mid-size right now and just becoming obvious to many people. I’ve heard reports in North Smithfield and Cape Cod about gypsy moth caterpillars covering houses. It was pretty dry in May, but I’m hoping we’ve had enough wet weather to allow the 2 diseases to spread and start killing gypsy moth caterpillars soon. The diseases don’t start spreading until caterpillars are at the 3rd instar stage, which is what I think most gypsy moth caterpillars are right now. I haven’t seen any dead gypsy moths yet.
gypsy moth caterpillars 3rd or 4th instar

Eastern tent caterpillars have been numerous this year, but these feed only on wild black cherry, apple, and crabapple (perhaps they feed on a few other shrubs, but not many). Eastern tent caterpillars are finished feeding for the year and are now wondering around looking for a spot to form a cocoon. Eastern tent caterpillars have one pale stripe down their backs.
Eastern tent caterpillar

Forest tent caterpillars are poorly named because they do not form tents. They are closely related to Eastern tent caterpillars, but forest tent caterpillars are forest defoliators. Forest tent caterpillars are defoliating trees in Richmond, Charlestown, and South Kingstown. If you are seeing defoliation from forest tent caterpillars in other towns please let me know. Forest tent caterpillars feed primarily on oaks, but once they are big – like now – they feed on many hosts. Forest tent caterpillars should be mostly finished in a week or so. Forest tent caterpillars have 2 blue stripes and many pale diamonds (or foot prints) in a row down their backs. They may be found singly or many gathered together on branches and tree trunks.
forest tent caterpillar forest tent caterpillars together

As for control – no need to control winter moth or Eastern tent caterpillars. Forest tent caterpillars are nearly finished for the year and I don’t think a Bt insecticide will work now since the caterpillars are so large. Other insecticides may be effective controlling forest test caterpillars, but I think it is best to wait for them to be finished.

Gypsy moths will be feeding for another few weeks and are starting to damage trees. I think gypsy moth caterpillars are still small enough to be controlled by a Bt insecticide (such as Dipel), but I’m not sure. Bt insecticides work best controlling small caterpillars. Other insecticides labeled for gypsy moth will also be effective, but of course there are other risks using pesticides.

Soon gypsy moth caterpillars will be climbing up and down tree trunks daily. They will feed in trees at night and walk down trunks to be in shade during the day. For this reason, sticky tree bands or burlap wrapped around a tree trunk can catch gypsy moth caterpillars. If you put burlap around a tree, you need to check under the burlap each day and remove caterpillars and kill them. And if you use a sticky band, you will probably need to remove stuck caterpillars daily.

Good luck and take an umbrella if you walk in the woods to keep the frass off.
Other apple pests:
Please watch your apples and blueberries for caterpillars. Yesterday in Richmond I saw some blueberry bushes totally destroyed by forest tent caterpillars. Spray accordingly!

For tree fruit growers:
According to Orchard Radar, Plum Curculio will finish migrating into orchards by June 5 in the Greenville area and June 11th in Newport County. Pesticide applications made 7 days or fewer from these dates should provide adequate coverage to control plum curculio. If you are worried that rain on Monday washed off too much insecticide, scout fruit on trees near woods or stone walls for fresh plum curculio scars. If you don’t find fresh damage you shouldn’t need to spray.

Apple scab primary season is over. I haven’t seen ANY scab lesions this year, but I haven’t looked very much either. Jon Clements from UMass did report finding scab lesions. Over the next week look thoroughly for scab lesions, and for fire blight strikes. Let me know if you find some of either.