If you are having problems with the needles on pines turning yellow, check for Dothistroma Needle Blight (Mycosphaerella pini) as it has been very common this spring. Scots pine is considered resistant.
This fungal disease causes the tips of needles to turn yellow, and yellow to tan bands to form along the needle. The black fruiting bodies have erupted through the surface of the needle. Needle blight is most serious on Austrian and Ponderosa pines and also can affect Mugo pines.
Winter desiccation can cause these same needle-yellowing symptoms, including banding, but does not exhibit the black fruiting bodies. This also is very common this year likely due to the extreme cold we had on December 18.
Though less common this spring, there can be other causes of yellowing needles. Brown spot (Scirrhia acicula) looks much like Dothistroma but affects primarily Scots pine. Ponderosa pine also is susceptible to brown spot, but Austrian pine is resistant.
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.
Some copper-containing fungicides can be used for control of Dothistroma needle blight. 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 the 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 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 which problem you have, now would be a good time to take a sample to your local K-State Research and Extension office so they can send it to the K-State Plant Pathology Lab for positive identification. (Ward Upham)