Diplodia Tip Blight
Pest Management Fact Sheet #5102
This disease can be very destructive to two- and three-needle pines. Commonly attacked are Austrian, mugo, Scots and red pines, but all pines and some other conifers are susceptible. The causal fungus is Sphaeropsis sapinea (= Diplodia pinea), which commonly infects trees planted outside of their natural range. Damage to native trees is not commonly seen.
The most readily observed symptom is the curling and death of new shoots, that have become infected in the early spring. Before this, needles can be seen to yellow and turn brown before they have fully expanded. Fruiting bodies (pycnidia) of the fungus can be seen as black dots at the base of the needles, especially toward the end of the season. Pycnidia are often found under the needle sheaths and can also be found on the cone scales and the shoots. The disease tends to be most severe on older trees and is less common in the nursery. Although symptoms can be found in all parts of the crown, the lower branches tend to be more severely infected because of the manner in which the fungal spores are washed down through the tree by the rain. The fungus can also infect stems through wounds, leading to resinous cankers.
The spores of this fungus can germinate and infect the tree over a wide range of temperatures. Although the spores require free water, 12 hours of wetness is sufficient for infection. During a wet spring, spores will be produced in great numbers and are readily spread by the splashing of rain. Trees that are in poor health due to environmental or cultural stress are more susceptible to infection than are healthy trees.
Survival and Dispersal
The fungus overwinters in diseased needles, cankers, and especially in two-year-old cones, which accounts for the increased incidence of the disease in older trees. The fungus survives well on dead plant tissues and produces spores within a year after infection. These spores ooze out of pycnidia during wet weather and are carried to susceptible tissue by the splashing of rain. Especially vulnerable to attack are the newly developing needles and shoots as well as second year cones.
- Maintain the health of the tree by avoiding improper sites. Control insects, fertilize and water during droughts.
- Pruning infected shoots is of little value in preventing new infections, although the tree will look better. Avoid pruning during wet weather and sterilize pruning shears to minimize spore dispersal.
- Protective fungicides available for control of this disease must be applied during the spring just before bud break and periodically thereafter to protect new growth as it expands. Fungicides that are appropriate include: Bordeaux mix and thiophanate-methyl.
When Using Pesticides
ALWAYS FOLLOW LABEL DIRECTIONS!
Pest Management Unit
Cooperative Extension Diagnostic and Research Laboratory
17 Godfrey Drive, Orono, ME 04473-1295
1.800.287.0279 (in Maine)
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