• Pine wilt is a lethal disease caused by a parasitic native nematode (tiny roundworm), carried to trees by a wood borer insect–the pine sawyer beetle . 
  • The main visual symptoms are needles quickly turning straw colored or grey. 
  • Exotic pines including Scots, Austrian, and mugo are susceptible to infection by the nematode. 
  • Native pines are not susceptible to this disease. 
  • High summer temperatures are required for the nematode to develop in the beetle and within infested trees – usually manifests in late summer. 
  • The disease is now a threat in both eastern and western Colorado. 
  • It can be prevented by timely sanitation and chemical injections. 

  Variations of this question might include: why is my pine suddenly wilting? or why did my pine tree all of a sudden turn grey or straw colored?

Pine wilt can seem to appear overnight but can also turn more the needles over a gradual, month-long period. 

pinewilt cycle

I’m worried my pine trees might have or might get Pine wilt!

Contact ArborScape for a fast, no-obligation tree care consultation! 

Keeping your Austrian and Scots pines watered and if necessary, fertilized for proper nutrition, may make the tree’s natural immune system strong enough to prevent it from becoming a target. The sawyer insect itself will be attracted to certain tree species such as an Austrian pine (the target plant). However even if the species is the right target species, botanists have observed that the sawyer won’t attempt an attack on a young tree, less than ten years old, and one that is in a healthy condition.

Our PHC team will start discussing winter watering options with you as we head toward the end of the season. It’s our professional arborists’ advice that you consider this option, as proper watering in the winter is a make or break factor for many trees – especially non-native species that are prone to pine wilt.

See winter watering overview and benefits here.


  • Sanitation – Trees killed by pine wilt in late summer or fall should be removed and destroyed before the emergence of pine sawyers in late May of the following year.
  • Do not leave stumps above ground level and do not save infested wood for firewood or transport infested logs.
  • Diseased trees should be chipped, burned or buried. There is minimal risk in moving the nematode in wood chips; therefore chips can be used for landscaping purposes.
  • Because adult pine sawyers infested with PWN may be attracted to any freshly cut pine logs, even native pine logs, and the PWN can potentially persist and multiply in these cut logs by feeding on blue stain fungi, do not store any fresh pine wood (firewood, logs, etc.) near exotic pines.


Pine wilt resources:
Pine Sawyer Beetle fact sheet

Pine wilt article @ CSU Extension

Pine wilt fact sheet


a pine tree exhibiting symptoms of pine wilt
from American Phytopathological Society fact sheet


last updated:

Jul 12, 2019 @ 9:32 am


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