Remember the pine butterfly outbreak that hit Grant County and other parts of the region from 2009 to 2012? In some of the more heavily affected areas, such as south and east of Seneca, the clouds of white butterflies looked like a summertime blizzard, and thousands of acres of pine forests were heavily defoliated. After the butterfly populations suddenly crashed, everyone was relieved that, overall, trees seemed to recover well and mortality was light.
However, the 2018 aerial survey of tree mortality has indicated a notable increase in tree mortality, particularly in those areas that had experienced the most defoliation.
Dr. Dave Shaw, forest health specialist for Oregon State University Extension Service, came to John Day on Oct. 16 to investigate and lead a forest health tour for interested woodland owners. According to Shaw, the pine forests were sucker punched by the prolonged drought that followed the defoliation event, greatly exacerbating the stress on trees.
Other conifer tree pests are quick to take advantage of trees weakened by stress, and in this case, the western pine beetle (Dendroctonus brevicomis) has really moved in. Usually, WPB is a relatively low-level problem, compared to its infamous cousin the mountain pine beetle (Dendroctonus ponderosae) that has killed millions of acres of trees across the U.S. and Canada in recent years. But now we’re seeing large numbers of trees killed by the WPB.
Another concern is that there are indications of a growing Douglas-fir tussock moth (Orgyia pseudotsugata) population in the same region where the pine butterfly defoliation was high. The tussock moth is appearing in the higher elevation, mixed-conifer forest types, and we could not find extensive defoliation on our short tour, but it seems to be building in numbers and may be more evident by next year. The tussock moth is typically a short-term defoliator with populations rising sharply then dramatically crashing from the combined effects of parasites, predators, disease and starvation, but we’ll have to see how this outbreak develops.
Shaw chopped away the bark on some of the ponderosa trees to reveal the unique spaghetti noodle-like pattern that the WPB leaves on the surface of the wood by eating away the cambium layer. But further chopping at ground level and below revealed a distinct stain in the wood. Blue stain fungi is common in pine trees that have been killed by WPB and MPB, lowering the commercial wood value, but is a result, not a cause, of mortality. However, Shaw expressed concern that this stain resembled that of the black stain root disease, which is common in southwestern Oregon but usually not here. He took some samples to have the stain positively identified in the lab, and we’re waiting to hear the results. Stay tuned!
Bob Parker is the Baker and Grant County Extension forester. For more information about these and other forest pests, visit fs.fed.us/foresthealth/protecting-forest/forest-health-monitoring/monitoring-forest-highlights.shtml.