Farmall Cub

I have white worms/caterpillars eating the needles on my white pines again.
They only bother the smaller (under 10 ft) trees and are killed with a water and detergent mix. I have been spot spraying the groups with a hand sprayer and spraying the entire tree with a garden hose sprayer.
They are similar to the tent worms but don't build a tent. They don't bother the spruce or arbavitae(?) next to the pines.

Does anyone know a preventative measure to keep them away?

From a retired county agent:

You might want to consider this:

"WHITE PINE SAWFLY STILL ACTIVE. Joe Boggs received a sample of white pine sawfly larvae (Neodiprion pinetum) from an arborist from SE Indiana, just across the river from Cincinnati, Ohio. This sawfly is a pale yellow to white colored larva with a black head and four rows of black spots along its body. It feeds primarily on white pine but will attack red, Mugo, and other short-needled pines. Larvae are present between mid-June and late-July, and sometimes for a second generation between mid-August and late-September. The larvae feed on both old and new foliage, so their feeding may result in complete defoliation of branches. Depending on how severe the defoliation is, the tree might be able to grow new needles next spring or it might die before the next growing season. If the stripped branches do produce needles, the trees might look odd because of the lack of old needles behind the new needles.

Sawfly larvae can be managed with insecticides such as Orthene or Sevin. Treatment should have been made when larvae were small and first began feeding on needles. Older larvae are susceptible to these sprays, but the damage to the host plants is already done. This is a pest to watch for next season, beginning in July."

Good luck.

Bill

Thanks for the info, that sounds exactly like what I have had.
I usually see them real late July but more toward early Aug.
I will be prepared next year.