|Biology and Symptoms
Sphaeropsis shoot blight, formerly called Diplodia shoot blight, is worldwide in distribution and can infect many conifer hosts. Although many pine species are reported hosts, this disease causes severe damage only to trees that are predisposed by unfavorable environmental conditions. Non-native, exotic pine species growing outside their natural range are especially vulnerable to attack. Other predisposing environmental factors include poor site, drought, hail or snow damage, compacted soils, excessive shading, insect activity or other mechanical wounding. In the north-central United States, the most common hosts are Austrian, Scotch, mugo, red and jack pines grown in ornamental and windbreak plantings.
Straw-colored shoots with stunted needles are diagnostic symptoms of Sphaeropsis shoot blight (Figure 1). Resin often exudes from infected shoots, gluing needles in place. In trees that are relatively free from stress, this disease kills only current-season buds and
|shoots, and 2nd-year cones. Older twigs and branches are damaged only if they are mechanically wounded or the tree's natural defenses are impaired by environmental stresses. Symptoms can be distinguished from insect damage by the persistent needles and absence of insect tunnels and frass.|
Under weather conditions favorable for infection, the fungus penetrates succulent stems through the intact epidermis and enters needles through stomata. The fungus may also infect through fresh wounds inflicted by insects, hail or other damaging agents. Cankers develop on infected shoots, branches and main stems and appear as elongate, sunken areas (Figure 2). Cankered tissue is resin-soaked, discolored and often exudes resin. Cankers may girdle branches or the main trunk, resulting in top killing and individual branch dieback. Tiny, black pimple-like spore producing structures form on infected needles (Figure 3), shoots, and cones (Figure 4). Infected cones become literally covered with these spore producing structures and become important sources of inoculum that causes new infections. The fungus overwinters within these structures and releases spores the following year during wet weather. Peak infection occurs after bud break in the early spring and during shoot and needle elongation. Infections that occur in the spring will first become evident in early to mid summer.
Since pine trees under stress are prime targets for attack, maintaining trees in good vigor is the best line of defense. Match the tree species to the proper site. Take care to avoid wounding trees, and do not prune or shear in wet weather when spores are being released. Water trees during dry periods to alleviate drought stress. Prune out and destroy dead shoots and branches, cutting back to a branch node and at least 12 inches ahead of any signs of infection. Severely damaged branches should be pruned back to the main stem. Remember, all pruning should be done during dry weather when bark surfaces are dry.
Fungicides are labeled for control, but they must be applied at least twice during the spring; once at budbreak and repeated at 2 week intervals until needles are fully elongated. Adequate chemical coverage on large trees is difficult and often requires specialized spray equipment. For the Midwestern States of MN, MI, WI,
|IA, IN and IL, fungicides containing the active ingredient thiophanate methyl, including trade names such as Clearys 3336, Fungo, and Domain, are labeled for control. Bordeaux mixture is also labeled for control. Check with your State Extension Service or local Extension office for further information on fungicides labeled for your specific area.|
improperly can be injurious to human beings, animals, and plants. Follow the
directions and heed all precautions on labels. Store pesticides in original
containers under lock and key - out of the reach of children and animals - and
away from food and feed. Apply pesticides so that they do not endanger humans,
livestock, crops, beneficial insects, fish, and wildlife. Do not apply
pesticides where there is danger of drift when honey bees or other pollinating
insects are visiting plants, or in ways that may contaminate water or leave
illegal residues. Avoid prolonged inhalation of pesticide sprays or dusts, wear
protective clothing and equipment, if specified on the label.
If your hands become contaminated with a pesticide, do not eat or drink until you have washed. In case a pesticide is swallowed or gets in the eyes, follow the first aid treatment given on the label, and get prompt medical attention. If a pesticide is spilled on your skin or clothing remove clothing immediately and wash skin thoroughly.
NOTE: Some States have restrictions on the use of certain pesticides. Check your State and local regulations. Also, because registrations of pesticides are under constant review by the U.S. Environmental Protection Agency, consult your local forest pathologist, county agriculture agent, or State extension specialist to be sure the intended use is still registered.
|Author:||Jill D. Pokorny, Plant Pathologist|
|For additional information contact:||Northeastern Area, S&PF
USDA Forest Service
Forest Health Protection
1992 Folwell Ave.
St. Paul, MN 55108
Phone: (651) 649-5262
FAX: (651) 649-5238