This fungal disease was originally called Diplodia blight, changed to Sphaeropsis blight, and is now, once again, named Diplodia blight. You may find it as Diplodia pinea or Sphaeropsis sapinea in the literature.
Diplodia blight is one of the most common landscape diseases on pines in Illinois. The fungus is an opportunistic or stress pathogen. Drought, heat, shade, frost, and insect damage may all predispose trees to infection. It is having a heyday this year. It does not take much effort to find a pine with this disease. Most pine species grown in Illinois are susceptible to Diplodia blight, especially Scotch, Austrian, and mugo pines. White pine is rarely affected.
The Diplodia fungus infects healthy, unwounded new needles, as well as trees that are experiencing stress. A characteristic symptom of this disease is the blighting of all needles at branch tips. When this occurs, most of the needles in the terminal 4 inches of growth turn brown, dry out, and may remain attached to the stem throughout the season. Often the tree develops new growth below this dead area, resulting in a zigzag pattern of stem growth. Look now for dead needles holding onto stem tips. Diplodia may also cause sappy stem cankers. If the canker girdles the stem, the tissue beyond the canker dies. This disease is not known to cause tree death but can cause some very unsightly damage.
Symptoms alone may not be distinct enough to confirm disease diagnosis. Some common look-alikes include drought, other canker disease, Dothistroma blight, and pine wilt disease. The presence of fruiting bodies of the causal pathogen clinches the diagnosis. Look for black, pinheadsized fruiting structures of the fungus on brown needles at the affected branch tips, on stems, and on cones. These structures do not rub off. They are embedded in the affected tissue, often more prominent at the base of needles, under the sheath.
It is not an easy task to control this disease completely. Cultural controls play an important part in the management of Diplodia blight. To reduce disease inoculum, prune and remove the dead wood or needles from the pine. To reduce the spread of the disease, removal of the dead tissue should be done in the early spring before buds open but when the foliage is dry, or during the dormant season. Removing all of the infected cones helps prevent pathogen overwintering, thus reducing disease inoculum the following spring. If possible, it is a good practice to alleviate any stress to your pine, especially by watering during times of drought.
Systemic fungicides are available to control this disease; however, if used, they should be applied only in conjunction with the cultural controls just listed. Fungicides for use against Diplodia are listed in the Illinois pest management handbooks. There is some debate in the literature as to their usefulness once a tree is infected. For more details about this disease, read the Report on Plant Disease, no. 625, “Sphaeropsis Blight or Diplodia Tip Blight of Pines,” available in University of Illinois Extension offices or on the Web at http://www.ag.uiuc.edu/%7Evista/. Bosnian pine (Pinus heldreichii) has been touted as a good replacement for Austrian pine because of its resistance to Diplodia blight.