Managing Dothistroma and brown needle blight on pines

Scotch, Austrian and white pine are susceptible to several needle blights that cause needles to brown, shed prematurely and may eventually kill the tree.

The two most common needle blights Michigan State University Extension educators and specialists find on pines in Christmas tree plantations are Dothistroma and brown spot needle blights. Symptoms of these diseases are very similar and knowing the tree species and when you are seeing the symptoms can help you identify which one you may have.

Dothistroma needle blight

Dothistroma needle blight is caused by the fungus Mycosphaerella pini Rostr. This common pine pathogen kills needles of all ages and can weaken or kill Austrian pine trees. Recently, we have also found Dothistroma on white pine. The main symptom is dead needle tips beyond the yellow to tan needle spots. These spots enlarge to form distinct brown to reddish-brown bands.

Needle tips turning brown on Austrian pine.
Photo credit: Jill O’Donnell, MSU Extension

The black fruiting bodies of the fungus can be seen in the dead spots or bands on the needles. The spores spread by wind and rain and can infect needles throughout the growing season. New needles are susceptible once they emerge from the needle sheaths. The black fruit bodies appear in the fall; however, the spores are released the following spring and summer.

The best protection of new needles can occur when applying copper-based materials as the new needles emerge from the needle sheaths and as the spores are released from the fruiting bodies. To protect foliage from infection, apply a registered fungicide containing copper or mancozeb in mid-June through mid-July. This year (2013), you might start earlier since trees are ahead of normal. Repeat the application two or three times as needed at seven- to 10-day intervals.

Brown spot needle blight

Brown spot needle blight (Mycosphaerella dearnessii, syn. Scirrhia acicola) is relatively new to Scotch pine in Michigan. Needle spots can appear on needles at any time of the year, but most commonly we find them during August and September when the tree suddenly turns brown just before harvest.

Bottom of Scotch pine trees browning in August-September.
Photo credit: Jill O’Donnell, MSU Extension

Even though we see the symptoms in the fall, fungicide applications should be timed when the new needles are about half grown (May-June) and a second spray about three weeks later. In rainy conditions, the spray interval may need to be shortened. Several fungicide products with chlorothalonil, mancozeb or copper are labeled for control.

Black fruiting bodies on dead needles.
Photo credit: Jan Byrne, MSU Diagnostic Services.

Growers will also want to adjust their shearing practices to avoid moving spores into other plantations.

  • Do not shear infected trees during wet weather because spores released at this time may be carried from tree to tree on workers’ clothes or shearing tools.
  • Sterilize tools after shearing affected plantations by dipping in denatured alcohol for three minutes.
  • Shear healthy plantations first so spores will not be carried into them from affected plantations.

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