It may not be winter injury on your Douglas fir
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
those of you growing Douglas fir Christmas trees, if you think you are
seeing browning or bronzing of needles on your trees when looking at
them from a distance, don’t assume its winter injury. Take a closer look
because it might be the needle casting disease called Swiss needle
cast, caused by Phaeocryptopus gaeumannii.
This needle cast disease can be infecting your trees for up to three years before you notice any symptoms; but whether it is the stress of winter, other stresses or a combination of events, we have seen this disease express its fruiting bodies with symptoms exploding on trees in early spring as the trees come out of winter. This infection can limit the trees’ market potential and you may need to apply sprays for up to three years in order to mask the damage. So, take a closer look at those brown or bronzing branches on your Douglas fir.
With the appearance of these fruiting bodies, a new cycle of Swiss needle cast begins when the fruiting bodies are formed in the spring. Look for two bands of little black specks along each side of the needle’s bottom surface. A whitish, waxy looking plug normally sits where the black fruit bodies erupt through the needle’s surface. Both the white plug and the black fruit body are easily seen with a magnifying lens. The white plugs are normal, but the black erumpent fruit bodies are a sign of the fungus indicating needle infection. Rainfall is essential for the microscopic spores to release from the fruit bodies. The disease is more common on needles located on the lower branches of the trees. Rainwater is essential for spore release and temperature plays a minor role, if any. Therefore, cool, wet springs and warm, wet springs will release Swiss needle cast spores in the plantation.
To prevent these spores from continuing their infection cycle, chemical preventatives should be applied when the new shoots are one-half to two inches long. A second application is usually required within two to three weeks. A third spray may even be necessary if the spring continues to be wet.
Dr. Fulbright's work is funded in part by MSU's AgBioResearch.