![]() ![]() “Swiss needle cast disease has been a problem in coastal Douglas-fir since the 1990s,” says Ahrens. The disease produces a pale overall appearance and sparse crown as individual needles turn yellow and drop. Swiss needle cast diseaseĭouglas-fir trees in some foothills around the Willamette Valley are afflicted with Swiss needle cast. Grand fir and noble fir are vulnerable to engraver beetles ( Scolytus ventralis), which attack true firs of all sizes. Insect pests that take advantage of drought-stressed trees include the Douglas-fir engraver ( Scolytus unispinosus) and the pole beetle ( Pseudohylesinus nebulosus). The cankers can coalesce to girdle branches or stems, and also can become sites of attack by bark beetles. Grand fir around the Willamette Valley is notorious for health problems due to drought followed by secondary agents such as bark beetles and fungi.Īhrens has observed that drought-stressed Douglas-fir trees are often afflicted with Dermea or Phomopsis stem canker fungi - normally weak pathogens that become damaging in trees under stress. Subsequent problems can ensue when secondary insects or diseases take advantage of a tree’s weakened condition.ĭouglas-fir is most commonly affected, but similar problems occur with other conifers including grand fir, noble fir, western redcedar and western hemlock. Heat and drought can kill trees outright or just put the trees under severe moisture stress. Similar drought damage events have recurred over the last 15 years, including in 2013. Possible stressors include long, dry summers ending with a hot period, followed by an early freeze and then a relatively warm winter.ĭrought-related injuries to the stem and leader are not always apparent when they occur, but often show up the following spring as the weather warms up and it’s time for trees to grow. Possible stressors include last year’s long, dry summer ending with a hot period, followed by an early freeze in November and then a relatively warm winter. ![]()
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