Winter moth and apple scab

Winter moth caterpillars may still not be very visible, but they are out there. Caterpillars are about half their mature size, so the next couple of weeks is when caterpillars do the most feeding and cause the most damage to shade trees. I expect caterpillars to start dropping to the ground to pupate in about 2 weeks.

Now is a good time to spray most landscape trees to control caterpillars. I prefer using a Bt insecticide such as Dipel because it kills only caterpillars and not other insects. The main problem with Bt insecticides is it lasts for only 3-5 days so additional sprays may be needed. Also, it is not as effective against large caterpillars, so it should be applied soon before caterpillars get much larger. Winter moth caterpillars are pretty easy to kill so most labeled insecticides are effective.

Some trees that are just leafing out have impatient caterpillars, like the pictured caterpillar on a white oak.


Looks like there could be an apple scab infection period on Thursday afternoon. With warm temperatures this week there is a lot of new growth and this should be protected with an fungicide before the next infection period.

Next Thursday, May 19th at 5:30 is our twilight meeting at Phantom Farms in Cumberland, RI.Phantom Farms is very easy to find. Take exit 11 off 295 for Route 114 north. Phantom Farms is 1 1/2 miles north on the left – you can’t miss it.

2920 Diamond Hill Road, Cumberland.

Rhode Island twilight meetings are free to RIFGA members ($40 yearly dues) or $20 for non-members. Two hours of pesticide recertification credits are available.