Dothistroma needle blight
Have you been noticing premature needle drop on your pine trees? Are the needles turning yellow? If so, you probably have Dothistroma needle blight. This disease tends to be more severe in crowded plantings.
Dothistroma needle blight is a fungal disease that causes the tips of needles to turn yellow. Yellow to tan colored bands form along the needle. There will also be black fruiting bodies (fungal spore-producing structures) that erupted through the surface of the needle. The biggest indicator of this disease is the tip of the needle turns brown, but the base stays green for several months. This disease is usually the most severe in the lower part of the tree and on the interior older needles. Needle blight is most serious in Austrian and Ponderosa pines, but can also affect Mugo pines. Scots pine is considered resistant to this disease.
Dothistroma needle blight is often confused with other pine disease. Winter desiccation can cause these same needle-yellowing symptoms, including banding, but does not exhibit the black fruiting bodies. However, less common, brown spot looks much like Dothistroma but affects primarily Scots pine. Ponderosa pine also is susceptible to brown spot, but Austrian pine is resistant.
Tip blight
Tip blight, another disease, can affect Austrian, Ponderosa, Scots and Mugo pines, but Austrians are most susceptible. This disease normally kills tips of branches when the needles are about half-grown in the spring. This disease results in the death of the entire needle, not just the tips. If the tips of branches are dead and the needles on these branches are shorter than normal, suspect this disease.
A form of control of Dothistroma needle blight is copper-containing fungicides. A single fungicide application in early June normally will protect foliage from infection. There is some risk in a single application because susceptible older needles are not protected in late May. Two fungicide applications in mid-May and mid-to-late June provide a more complete and dependable control.
Make sure all needles are thoroughly covered with fungicide. It is a good idea to spray adjacent susceptible pines. It may take multiple years of application to bring the disease under control. Copper fungicides are suggested for control such as Junction, Kocide, Camelot, Bonide Liquid Copper Concentrate and Monterey Liqui-Cop. Collection and removal of diseased needles on the ground around individual trees may reduce the severity of infection the following year. Nevertheless, sanitation probably will not eliminate the disease because the diseased needles bearing fruiting structures of the fungus sometimes remain attached to the tree. Removal of dead needles is impractical in windbreak plantings. If you are unsure of which pine disease you may have or have any questions feel free to stop by or contact me in the Washington office at 785-325-2121 or [email protected].