Disease

Sphaeropsis shoot blight and canker caused by the fungus, Sphaeropsis sapinea (formerly Diplodia pinea).

Importance

Sphaeropsis causus shoot blight and stem canker of red pine in nurseries (fig.23), plantations, windbreaks (fig.24), and ornamental plantings throughout the lake States. Although Sphaeropsis may attack healthy trees, the fungus usually attacks trees stressed by one or more of the following factors: poor site, drought, hail damage, snow damage, mechanical wounds, and insect activity. Sphaeropsis kills trees by killing the new foliage year after year or by initiating girdling stem cankers on stressed or injured trees.

Figure 23	Figure 24

Biology

Figure 25

Shoot blight (fig. 25) and branch and stem cankers (fig. 26) are the most common symptoms of Sphaeropsis. Shoot blight is common on trees of all ages, but cankers are more prevalent in saplings and pole-sized trees than in large trees. All symptoms are generally characterized by conspicuous amounts of resin. Sphaeropsis overwinters as mycelium or fruiting bodies in shoots, bark, cones (fig. 27), or litter. Spores (conidia) are disseminated during wet weather in spring through fall. Peak spore production and infection usually coincide with host bud break and shoot and needle elongation. The fungus first invades and kills succulent shoot tissue and then forms fruiting bodies on dead tissues (fig. 28). Spores from current-year infections may be disseminated in the same year or the following year. Infection can also occur through wounds caused by various agents such as hail and insect feeding. The fungus invades woody tissue under such conditions.

Figure 26	Figure 27

Figure 28

Management Guidelines

Prevention is the best way to control Sphaeropsis.

• Avoid planting red pine in areas where Sphaeropsis has been a problem.

• Do not plant red pine on poor sites, particularly sites subjected to periodic severe droughts.

• Prevent logging or other wounds, particularly during peak spore dispersal (May through August).

• Avoid planting red pine seedlings adjacent to infected conifer windbreaks.

• Do not shear infected Christmas trees while foliage is wet to avoid transferring Sphaeropsis spores to healthy trees by shearing tools.

• Plant red pine on the best sites. These trees will be more vigorous and their wounds will heal more quickly, reducing the chance for Sphaeropsis infection. If infection does occur, the impact of the fungus infection will not be as great as on a stressed tree.

Nicholls, T.H.; Ostry, M.E. 1990. Sphaeropsis sapinea cankers on stressed red and jack pines in Minnesota and Wisconsin. Plant Disease. 74 (1): 54-56

Palmer, MA.; Nicholls, T.H. 1983. How to identify and control Diplodia shoot blight, collar rot, and canker of conifers. St. Paul MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 8 p.

Palmer; MA.; Nicholls, T.H. 1985. Shoot bllght and collar rot of Pinus resinosa caused by Sphaeropsis sapinea in forest tree nurseries. Plant Disease. 69(9): 739-740.

Palmer, MA.; Nicholls, T.H.; Croghan, C.F. 1986 Fungicidal control of shoot blight caused by Sphaeropsis sapinea on red pine nursery seedlings. Plant Disease. 70(3): 194-196.

Peterson, G. W. 1981. Diplodia blight of pines. For. Insect and Dis. Leafl. 161. Washington, DC: U.S. Department of Agriculture, Forest Service. 7p.