Managing Diplodia tip blight

Diplodia tip blight fungus can kill the current year shoots of Scotch pine, Austrian pine and, occasionally, spruce.

Diplodia tip blight (formerly known as Sphaeropsis) can kill the current year’s infected needles and stems of Scotch, Austrian pine and in some years we have even found Diplodia on spruce and white fir. The fungal pathogen, Diplodia sapinea, 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.

Diplodia symptoms
New shoot showing stunted and curled symptoms of Diplodia infection.

Diplodia fruiting bodies
Diplodia fruiting bodies in cones.

The last few rainy springs we have found Diplodia shoot severely infecting many Scotch 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. If you have had problems before with Diplodia you should consider 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.

Fungicide options include chlorothalonil + thiophanate-methyl (Spectro 90), thiophanate-methyl (Cleary’s 3336, Topsin M, etc.), mancozeb (Protect DF, Penncozeb, Dithane, etc.) and copper hydroxide + mancozeb (Junction). The product you choose will depend on the site of the application such as Christmas trees, nurseries or landscapes. Read and follow label directions.

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