Caterpillars on pine trees

Asked March 12, 2015, 11:21 PM EDT

I live in Florentine Estates in Florence, Lane County, Oregon. Community representatives have cautioned residents about caterpillars that are"back" and are damaging to pine trees. I am a new resident here so am just becoming aware of this. I want to know what types of pine trees are assaulted, what types of caterpillars, and what treatment? BT spraying was recommended as well as spraying off with a hose. I have lived in the east and Michigan and am aware of different kinds of caterpillars on pines; not all build webs. Some are very specific as to which pines they attack. Can you tell me which trees I should be watching? What is the window when these pests appear, and how I can get ahead of them? I have looked at tall pines in the neighborhood and some small shrubs and have seen nothing. I am looking at the newly formed growth.

Lane County Oregon

1 Response

Can you email me a picture of the caterpillars you are seeing? I can't be sure which caterpillars you are referring to without seeing them.

The most common caterpillar that is obviously eating foliage this time of year is the silver-spotted tiger moth caterpillar. These caterpillars are social and form tents. They are present all winter long, but don't become noticeable until late winter and spring. They usually only defoliate a localized patch on a tree. Here is a link to the Oregon Department of Forestry document on the insect: Silver-Spotted Tiger Moth

Does this look like your caterpillars? These are generalist eaters; they go for pine, spruce, Douglas fir, hemlock, grand fir, whatever it appears. They have a one-year life cycle and do a boom and bust, where some years they are very common and some years rare.

Damage is not too severe because they do not eat the buds, and the tree typically has no long-term effects.

Best control is to knock the caterpillars into soapy water, or prune out the tents when they are aggregated and burn or dispose of them.

Pesticides are not used too much because the trees usually do fine. They just look bad for a few months in late winter and spring.

But of course I've been discussing the usual caterpillar we hear about this time of year, and I've heard from many folks already about this, and so it appears to be a banner year for the silver-spotted tiger moth! Again, I can't be sure which caterpillars you are referring to without seeing them.

If you'd like to send pictures: dave.shaw@oregonstate.edu.