Dothistroma Needle Blight of Pines
Mary Jane McReynolds, Extension Associate
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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 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
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.
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.
Liquid Copper, Tenn-Cop 5E
Fixed coppers, copper sulfate
Mancozeb, Dithane T/O
Chlorothalonil, Daconil Ultrex
Chlorothalonil, Bravo 500