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Extension > Garden > Yard and Garden > Trees and Shrubs > Dothistroma needle blight

Dothistroma needle blight

Rebecca Koetter and Michelle Grabowski

Importance

A.S. Munson USDA Forest Service, Bugwood.org

Young tree infected with Dothistroma needle blight has browning of older needles as well as bare branches from needle drop.

Dothistroma needle blight is a fungal disease that turns needles brown and results in early needle drop. Needle loss slows tree growth and severe infection several years in a row can result in tree death.

Pathogen and susceptible plants

Dothistroma needle blight is caused by the fungus Dothistroma septosporum (syn. Mycosphaerella pini). In Minnesota, plants most severely damaged by this disease include Austrian pine (P. nigra) and ponderosa pine (P. ponderosa) and to a lesser extent, mugo pine (P. mugo). Red pine (P. resinosa) and Scots pine (P. sylvestris) are generally resistant to this disease.

Identification

M. Grabowski, UMN Extension

Needle spots, bands and dead needle tips from Dothistroma Needle blight.

Biology

M. Grabowski, UMN Extension

Needle spots on current year needles and needle tip death on previous year's needles.

Dothistroma needle blight is a slow-moving disease that takes over a full year to complete its life cycle and several years to develop into a serious problem within the tree canopy. Spore producing structures known as stromata are produced within infected needles on trees. Spores are produced throughout the growing season whenever cool, wet weather occurs. These spores are windblown or rain-splashed to mature needles. Second year or older needles are susceptible to infection anytime during the growing season but new needles are resistant until they reach maturity in early to mid summer. At this point they become susceptible to infection. Several consecutive days of cool (41-77°F), wet weather are needed for successful establishment of new infections.

In Minnesota, symptoms do not typically appear until the fall when needles develop reddish brown spots. These spots expand into a reddish brown band that entirely girdles the pine needle. The needle beyond the band then dies and turns brown leaving the bottom portion of the needle green. Infected needles may remain attached to the tree for one or two years depending on the age of the needle at the time of the infection. Eventually infected needles turn completely brown and fall off prematurely. Tiny black fungal fruiting bodies appear in the bands or in dead areas of the needles. These fruiting bodies will release spores the following year to begin a new disease cycle.

Management


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