University of Nebraska Cooperative Extension in Lancaster County

Dothistroma Needle Blight of Pines

Compiled by
Mary Jane McReynolds, Extension Associate
087-00
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One of the most common diseases of pines in Nebraska is Dothistroma needle blight.  This disease is responsible for much of the premature needle drop that occurs in windbreaks and ornamental pine plantings.  Austrian pine “Pinus nigra”, ponderosa pine “Pinus ponderosa” and mugo pine “Pinus mugo” are all attacked by this fungus, but Scots pine “Pinus sylvestris” is not severely damaged by it.

Symptoms
Symptoms on Austrian and ponderosa pines begin to develop during the fall of the year of infection. Yellow to tan spots appear on infected current year and older needles. These oval to oblong spots will darken and become brown or reddish brown.  Bands also form on infected needles.  These bands are often bordered by a second, yellow, chlorotic band. The fungus grows within these tissues, killing that portion of the needle beyond the lesion. The end portion of the needle turns light green, then yellow and dies while the base remains green. Needles may begin to change color within two to three weeks after the initial appearance of symptoms. As the disease progresses, the base of the needle dies and the needles drop.

Typically, clusters of needles within a shoot are infected. Infection is usually more severe on lower branches, but can occur over the entire tree. Infected needles may be shed during the winter, but the greatest loss comes during late spring or early summer. Second year needles usually drop before current year needles, which often are not shed until the summer after the year of initial infection. In some cases, severely infected trees retain only current year needles. If a tree is heavily infected for several years, many of its branches may be killed and the whole tree may eventually die. 

Cause
The fungus produces spores in fruiting bodies, which develop in the spots and bans below the needle surface and mature in the spring following the year of infection. The spores are released from the fruiting bodies during periods of rain from May through October. Germinating spores enter needles through natural openings and the infection process begins. Symptoms appear about three to four months after first infections, usually becoming visible in late fall. First year needles are initially resistant to infection, becoming susceptible in mid-summer. Second year and older needles are fully susceptible to infection throughout the season.

Control
Infection of susceptible needles can be significantly reduced by fungicides applied twice during the growing season. The first application should be made in mid May and the second in mid to late June. The first spray protects the previous season’s needles and the second spray is necessary for protecting newly developing current season needles. Make sure that all needles are covered thoroughly with the fungicide.

Fungicides
Liquid Copper, Tenn-Cop 5E
Bordeaux Mixture
Fixed coppers, copper sulfate
Mancozeb, Dithane T/O
Chlorothalonil, Daconil Ultrex
Chlorothalonil, Bravo 500

 

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