Diplodia tip blight management in trees

Diplodia tip blight can attack trees of any age. Time fungicide applications to protect new growth from bud break through full candle elongation.

Brown, stunted new shoots are a common symptom of Diplodia blight on Scots pine. Photo credit: Jill O’Donnell, MSU Extension
Brown, stunted new shoots are a common symptom of Diplodia blight on Scots pine. Photo credit: Jill O’Donnell, MSU Extension

Diplodia tip blight (Diplodia pinea) can kill the current year’s infected needles and stems of Scots pine (Pinus sylvestris), Austrian pine (Pinus nigra) and in some years we have even found Diplodia on spruce, Douglas fir and white fir. The fungal pathogen Diplodia pinea overwinters in pine shoots, bark and cones and infects growing and elongating shoots in the spring. The black fruiting bodies are relatively large and can be seen easily with a hand lens and even the naked eye. These black dots will be on the needles, usually under the sheath, as well as on the stems and on the cones’ scales. The most common symptom of Diplodia blight is brown, stunted, new shoots with short, brown needles.

The last few rainy springs we have found Diplodia shoot severely infecting many Scots pine fields. During rain and windstorms, these spores will disperse over long distances and conditions for infection will remain favorable during rainy and humid days. The new shoots are most susceptible to infection from bud break until the needles are fully elongated.

If you have had problems before with Diplodia, Michigan State University Extension recommends applying fungicides beginning as the candles are expanding and then two more applications at 10-day intervals. This prevents the spores that are now being disseminated from infecting the succulent new growth. If, later in the summer, more than 10 percent of the trees have severe shoot blight, consider a spray program again next spring.

Management of Diplodia includes removing infected pines in fence rows, wind breaks or nursery blocks. Also, when practical prune and remove infected twigs and branches during dry weather. Apply appropriate fungicides in early spring. Fungicide options include chlorothalonil plus thiophanate, methyl (Spectro 90), thiophanate-methyl (Cleary’s 3336, Topsin M, T-Methyl, etc.), mancozeb (Protect DF, Penncozeb, Dithane, etc.), and copper hydroxide plus mancozeb (Junction). The product you choose will depend on the site of the application such as Christmas trees, nurseries or landscapes. Make sure to read and follow label directions.

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