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.

Austrian pine along the roadside with Dothistroma needle blight. Photo: Jill O'Donnell, MSU Extension.

Austrian pine along the roadside with Dothistroma needle blight. Photo: Jill O'Donnell, MSU Extension.

As spring arrives, we begin to see browning of pine needles in plantations, landscapes and along roadsides. There are several possible fungal pathogens that can cause these symptoms.

Dothistroma needle blight

Austrian pine is the primary species in Michigan where we see Dothistroma needle blight. The foliage of the lower half of the tree turns brown in March to April.

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.

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.

Dothistroma needle blight

Dead needle tips and needle base remains green. Photo: Jill O’Donnell, MSU Extension.

Brown spot needle blight

Brown spot needle blight (Mycosphaerella dearnessii, syn. Scirrhia acicola) is relatively new to Scots 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. Short-needled Scots pine varieties such as Spanish and French-green are more susceptible to fungal attack than the long-needled varieties.

Brown spot can be controlled by fungicidal sprays. The first application should be applied when the new needles are about half-grown (May-June), and a second spray three to four weeks later. The spray interval may need to be shortened in rainy conditions.

Brown spot needle blight

Brown spot needle blight symptoms on Scots pine. Photo: Jill O’Donnell, MSU Extension.

Black fruiting bodies

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

Lophodermium needlecast

Lophodermium is a severe needlecast of Scots pine, which in some cases can cause the entire tree to brown in spring. Even though we see the symptoms of Lophodermium in spring, the most important time to protect trees is from the end of July through September. This is when needles are infected from spores being released by the small, shiny, football-shaped, black fruiting bodies that form on the fallen needles. To break this disease cycle, the time to manage this disease with a fungicide is particularly in late July and throughout August, but maybe even into fall if it the weather stays warm and moist.

Lophodermium needlecast on Scotch pine.

Lophodermium needlecast on Scots pine. Photo: Jill O’Donnell, MSU Extension.

You can help identify the disease your trees have by knowing the species of pine and the time of year you first see the symptoms. To confirm which needlecast disease you have, send a sample to MSU Diagnostic Services. The cost for a sample is $20.

Pine tree disease overview

 Disease

Symptoms appear

Species

Timing of control

Dothistroma needle blight

March/April

Primarily Austrian but also on Red pine, Scots pine

May - July

Lophodermium needlecast

April/May

Primarily Scots pine but also found on Austrian and Red pine

August - September

Brown spot needle blight

August/September

Primarily Scots pine but also on Red pine, Austrian

May - June

Related Articles