SWISS NEEDLECAST ( Phaeocryptopus gaeumanni )
Swiss Needlecast is caused by a fungus which attacks only Douglas-fir. Infection occurs during Douglas-fir budbreak and shoot elongation. The fungus produces minute, spherical, black, fruiting bodies which erupt through stomata on the undersides of the infected needles and release spores to infect the new growth. It may look as if there are two tiny rows of soot on the underside of each infected needle.
Although the fungus infects the newly expanding needles, it usually does not kill needles until they are 2 to 3 years old. At that time, infected needles start to turn yellow and be cast from the tree. Infection occurs mainly near the base of the tree and may leave the lower foliage looking thin and unattractive, with many branches having only the current years growth remaining.
The black fruiting bodies may be found on the undersides of infected needles in the spring after infection occurs. This is the only definitive sign of infection you will be able to find, and the best place to search is in the lower crown. Fruiting bodies may also be found on needles which have already begun to turn yellow or brown but they may be from secondary fungi that resemble the Swiss needlecast fungus. Nevertheless, looking for discolored needles near the base of the trees may help you to find the disease. Scout for this fungus on a day that is cloudy or overcast as shadows accompanying bright sunlight make it difficult to see the discolored needles or fruiting bodies.
Fig. 1. The black soot-like spots on the undersides of these needles are the fruiting bodies (pseudothecia) of the Swiss needlecast fungus.
Swiss needlecast can be controlled with early season applications of a registered fungicide. Three applications are generally recommended with the first when at least 50% of the buds have broken and the new growth is 1/2 inch long. Make additional applications at 2-3 week intervals.
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