Sphaeropsis blight (formerly Diplodia blight) is common on Scotch, Austrian, and mugo pines in Illinois. It is rare on white pine. Infected trees may show branch tip dieback, with needles remaining attached throughout the season. Limbs of affected trees may have damaging, sappy cankers. Often, an infected branch dies beyond the site of the canker, resulting in a very unpleasant-looking tree. Severely infected trees may be confused with those killed by pine wilt.
Management of this disease is difficult. Most infection takes place in the spring, as new growth emerges. This tender growth is very susceptible to infection, especially in wet weather, until about mid-June. Infection is occurring now. We can suggest several methods to reduce Sphaeropsis blight. It helps to remove dead wood and needles to reduce the amount of the fungus in the area. To avoid increased spread of the disease, this should be done when the tissue is dry. It also helps to remove cones from the site. Cones on infected trees are usually covered with fruiting bodies of the fungus. These can be seen as small, pinhead-sized black bodies embedded in bud scales. Fruiting bodies contain spores that serve as inoculum for additional infection. The final point is that drought-stressed trees are more susceptible to canker infection. For that reason, we recommend watering infected trees in periods of extended drought. Supply an inch or more of water per week to pines in drought-stressed areas. Prune out dead branch tips and cankered wood in the next dry period. Remove it from the site.
There are chemical options available to control this disease. The recommendation is to try to use a systemic product and to apply it three times, following label directions. Usually this is as buds begin to expand, just before new needles emerge from the sheath, and 10 to 14 days later. Recent research on this disease has shown that even foliage without symptoms is often already infected. That research questions the use of chemicals that are intended to prevent infection. It is still strongly recommended that you follow the cultural controls discussed above. In fact, cultural controls are more important than ever in managing Sphaeropsis blight. The use of chemicals may still be of benefit but should be used only in addition to cultural controls. Do not rely on chemical control alone. Choose a systemic product from those listed in the Illinois pest management handbooks and follow label directions precisely. A table at the end of disease chapters lists all chemicals mentioned in that chapter and provides information on chemical mobility. For details on this disease, consult 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/horticul.htm.