Why are my pine trees turning brown?
Knowing the species of pine and the time of year you first see symptoms can help you identify the disease.
This year (2011), we are seeing severe Dothistroma needle blight in plantations, landscapes and along roadsides. Austrian pine is the primary species in Michigan where we see this disease. The foliage of the lower half of the tree turns brown in March to April (Photo 1).
Photo 1. Austrian pine along the roadside with Dothistroma needle blight.
Dothistroma needle blight is caused by the fungus Mycosphaerella pini. This common pine pathogen kills needles of all ages and can weaken or kill Austrian pine trees. Characteristic symptoms of Dothistroma infection is the presence of needles showing browning at the tip of the needle while the base of the needle remains green (Photo 2).
Photo 2. Dead needle tips and needle base remains green.
The black fruiting bodies of the fungus can be seen in the dead spots or bands on the needles. Dothistroma 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. This is usually June and July. Reports suggest that removal by pruning of infected branches helps reduce disease.
We have two other needlecast diseases where the symptoms closely resemble those of Dothistroma. These are Lophodermium needlecast and Brown spot needle blight.
Photo 3. Brown spot needle blight symptoms on Scots pine.
Photo credit: Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org.
Photo 4. Lophodermium needlecast on Scots pine.
Knowing the species of pine and the time of year you first see the symptoms can help you identify what disease your trees have. To confirm which needlecast disease you have, send a sample to MSU Diagnostic Services, http://www.pestid.msu.edu/. The cost for a sample is $20.
|Symptoms Appear||Species||Timing of control|
|Dothistroma needle blight||March/April||Primarily Austrian but also on Red pine, Scots pine||June - July|
|Lophodermium needlecast||April/May||Primarily Scots pine but also found on Austrian and Red pine||August - October|
|Brown spot needle blight||August/September||Primarily Scots pine but also on Red pine, Austrian||May - June|