Look on the undersides of needles for brown female covers and white male covers. May. The crawlers currently observed are probably from the second generation. Treat heavily infested trees with a systemic insecticide like Merit. Yellow-necked Caterpillar has been reported on oak Adult moths of this shade tree pest appear in June and July and larvae are usually found from July through October. One report listed larvae at 30 mm now.
Caterpillars feed in clusters near branch terminals.
Small trees can be completely defoliated. Manually remove caterpillars in light infestations or soak with a spot spray of horticultural oil. An email dialog among extension specialists this week focused on pruning of Christmas trees. This is the recommended time to prune true fir and douglas fir, but growers were wondering if trees should be pruned now with our existing drought. The specialists agree with this concern and recommend no pruning now.