Several
reports of sawflies defoliating Valley pine in Lane and Yamhill counties were
received in May of 2003. This sawfly is a native species of Neodiprion whose
outbreaks are of short duration and cause little damage. The larvae feed
gregariously on the older needles of ponderosa pine in the spring causing the
foliage to turn brown and landowners to be concerned.
With damaged brown needles present and the
new shoots and needles not completely expanded, trees appear to be suffering
significant damage. However, sawfly outbreaks in ponderosa 
pine
last only one or two years and do not kill trees. In the worst case, sawfly
defoliation only reduces growth. Usually sawfly outbreaks collapse quickly from
the combined effects of predators, parasites and disease on the population. The
use of insecticide to control sawflies is not warranted under most
circumstances.
Reports of sawfly defoliation of pine in the Willamette Valley were quite rare ten years ago. Undoubtedly Neodiprion populations cycled up and down in the past, but with so few host trees present the outbreaks went largely unnoticed. As thousands of acres are planted to ponderosa pine, sawfly outbreak cycles will become increasingly visible to landowners and foresters.
