Diplodia Tip Blight (Sphaeropsis Blight)

PP016 (5/03R)

By Dr. Sharon M. Douglas
Department of Plant Pathology and Ecology
The Connecticut Agricultural Experiment Station
123 Huntington Street
P. O. Box 1106
New Haven, CT 06504-1106

Telephone: (203) 974-8601 Fax: (203) 974-8502
Email: Sharon.Douglas@po.state.ct.us

Diplodia tip blight, also called Sphaeropsis blight, can be a destructive and devastating disease of pines, especially two- and three-needled species. Austrian, black, mugho, red, and Scots pine are very susceptible although many other species of pine are also affected, especially when growing under conditions of stress. Trees of all ages are susceptible, although older trees frequently sustain greater damage and disfigurement.

SYMPTOMS AND DISEASE DEVELOPMENT:
Diplodia tip blight is caused by the fungus Sphaeropsis sapinea. This fungus usually attacks only mature trees, although it is more damaging to trees that have been under stress from drought, excessive soil moisture, root restriction, other site problems or stresses. Symptoms often first appear on current-season needles since the fungus rapidly kills infected young, succulent shoots before the needles are fully elongated. Consequently, needles on such shoots are often stunted. Infected shoots turn yellow, gradually brown, and fruiting structures of the fungus are visible as small, black structures with conical beaks at the base of the infected needles. A diagnostic feature of Diplodia tip blight is the presence of stunted, straw-colored shoots with short needles and resin flow. In trees that are relatively free from stress, tip blight only kills the current-season buds and shoots and second-year cones. Older twigs and branches are damaged only if trees are predisposed by stress, especially due to drought. This results in blighting and deformation of branches and limbs. In extreme cases, Diplodia tip blight can result in tree death.

The Diplodia tip blight fungus can attack older shoots through wounds, including those caused by insect injury. These infections often result in perennial, bleeding twig and stem cankers but, in severe cases, can lead to girdling, branch death, and significant disfigurement of the tree. Recent research suggests that the fungus is capable of causing latent infections that can go undetected until the tree is exposed to periods of stress, at which time the fungus is activated and typical dieback symptoms develop.

Cones are also infected by S. sapinea. This usually occurs during their period of rapid growth in the spring. Although cone infections are inconsequential for the general health of the tree, they are important for their contribution to the spread and severity of the disease since they contribute considerable fungal inoculum. Fruiting structures of the fungus are readily seen as small, black bodies on the cone scales.

Diplodia tip blight is favored by wet spring weather, which promotes fungal growth and infection. Spores of the fungus are only spread during periods of rainfall and pines are particularly susceptible to infection in early spring. Once again, trees that are predisposed by stress are much more susceptible than their stress-free counterparts.

DISEASE MANAGEMENT:
The effects of Diplodia tip blight can be minimized by following a multifaceted approach to control that includes sanitary, cultural, and chemical methods. It is very important to prune and remove as many blighted twigs, branches, and cones as possible during dry weather in autumn. This helps to reduce the amount of the fungus available to infect the new growth in the spring. It is often necessary to sacrifice and remove severely symptomatic trees to reduce the amount of inoculum. Trees should also be kept as vigorous as possible by following sound cultural practices to maintain tree vigor, controlling insect infestations, and watering during periods of drought. All unnecessary stresses such as soil compaction or equipment injuries should be avoided, if possible. Fungicide applications can also supplement other control strategies. Among the compounds registered for use in Connecticut are copper sulphate pentahydrate, mancozeb, mancozeb plus copper hydroxide, propiconazole, and thiophanate methyl. Consult the label for dosage rates and safety precautions. Since these fungicides act as protectant materials, they must be applied to the new growth as it emerges in spring. The first application should be made before any bud sheaths have broken and two or three additional applications can be made at label intervals, as necessary.

Diplodia tip blight, also called Sphaeropsis blight, is caused by the fungus Sphaeropsis sapinea. This can be a destructive and devastating disease of pines. Austrian, black, mugho, red, and Scots pine are very susceptible although other species are also affected, especially when growing under conditions of stress. Symptoms first appear on young, succulent shoots and current-season needles, which develop a straw-colored appearance. This fact sheet discusses the symptoms, spread, and management options for this important disease.