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Dothistroma Needle Blight
Need to know:
- Brown bands will appear on infected needles and the portion beyond the band will die.
- Infection usually occurs first on the lower branches of the tree and spreads upward.
- Symptoms are similar to brown spot needle blight, but Dothistroma occurs primarily on Austrian and ponderosa pine and brown spot is more common on Scots pine.
- Avoid planting the highly susceptible Austrian pine. Dothistroma needle blight can be prevented by keeping trees in good vigor through watering and mulching, and promoting air circulation through appropriate pruning, adequate spacing, and weeding.
- Fungicide sprays may be used if symptoms are found and are applied in the spring.
Overview of Dothistroma needle blight
Dothistroma needle blight is especially common on Austrian pines.
Symptoms of Dothistroma needle blight
Dothistroma needle blight is a common fungal disease that causes browning of needles of Austrian, ponderosa, and mugo pines. Affected needles have reddish brown spots or bands. The needle tips beyond the bands dry out and turn brown a couple weeks after the bands appear, while the bases remain green. Diseased needles may drop prematurely, several months after they are infected. Typically, the most severely affected branches are towards the bottom of the tree. An entire tree may progressively lose its needles, decline, and die over the course of a few years.
Dothistroma needle blight is caused by the fungus Dothistroma pini (also called Mycosphaerella pini). The fungus is active throughout the growing season and can infect any age of needle during wet weather. However, symptoms typically first appear in early fall, although they may not be noticed immediately.
Type of Sample Needed for Diagnosis and Confirmation
The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if you plant has this disease. Please see our website for current forms and fees. Contact information for each states diagnostic laboratory for U.S. residents. If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us
To confirm Dothistroma needle blight we need to examine a sample under the microscope. Samples should include symptomatic needles, living and still attached to a branch. Branches can be packed into a box with paper towel for shipping. DO NOT add water to the samples. If you are uncertain about the type of sample feel free to contact us.
Management of Dothistroma needle blight
The best way to avoid Dothistroma needle blight in Iowa is to avoid planting Austrian pine. Austrian pines are very susceptible to both this disease and another disease, Diplodia tip blight, such that they are not a good choice for this area.
Where Austrian pines are already planted, Dothistroma needle blight can be prevented by inspecting trees carefully for fruiting bodies before planting and rejecting diseased trees. Avoid planting susceptible species next to infected trees. Promote good air circulation through adequate tree spacing and weed control. Improve tree vigor through cultural practices such as mulching and watering, as needed. Do not shear trees when foliage is wet.
If symptoms appear, a fungicide spray program, such as with Bordeaux mixture, copper fungicides, or EBDCs, can protect trees from further infection. Proper timing and good coverage are critical. Two sprays are applied, with the first in mid-May and a second spray a month later. This protects the needles from the previous year and the newly emerging needles. Fungicide sprays can be discontinued when symptoms have disappeared
Fungicide applications may be avoided by following good Integrated Pest Management practices like those listed in this encyclopedia article. Often, the only preventative application is effective to manage plant diseases. If the problem requires a fungicide, state law requires the user to read and follow all labels accordingly. For more information, read Proper fungicide use.
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