Diseases that attack the needles, twigs and leaves of forest and shade trees often develop into spectacular events. With the exception of a few, most of these fungi do very little harm to the tree. Christmas tree growers may experience severe defoliation during wet springs.
The most serious needle disease of pine is caused by the brown-spot needle fungus, Scirrhia acicula (Figure 55). Longleaf pine seedlings can be seriously damaged. Severe needle blight on young seedlings can increase the length of time it takes longleaf pine to grow out of the grass stage (Figure 56). The disease affects both planted and natural seedlings in the field.
Infected needles in the early stages are irregularly yellow to brown spotted, with green tissue in between the spots. Needles are eventually killed by the girdling action of the fungus.
Brown spot can be controlled in nurseries by spraying with an approved fungicide. Prescribed burning is recommended for control of the disease in plantations. Burns should be made only when the disease is causing damage, and weather conditions are favorable for burning.
Leaf blister of oaks is perhaps the most conspicuous leaf disease of the pointed leaf oaks such as scarlet and southern red. Certain of the entire leaf oaks are also attacked. The disease is more prevalent during wet springs. Infected leaves will have blister-like eruptions. Premature leaf lull is common while the leaves are only partially dead. The fungus overwinters on twigs and dead leaves. Raking up and burning the infected leaves as they fall will destroy overwintering spores thus reducing the source of innoculum for next year. Applications of an approved fungicide can be made in the spring just as the buds are swelling.
A disease of flowering dogwood caused by the fungus Discula spp. was discovered in Georgia during the 1987 growing season by U. S. Forest Service pathologists. The disease was cultured from dogwoods growing on the Chattahoochee National Forest in northwest Georgia. Initial symptoms are a small, purple rimmed spots and large blotches on the leaves (Figure 58). Dieback of small twigs occurs initially with larger branches dying later. The dieback usually progresses from the bottom to the top of infected trees. Death of the tree may occur in one to three years. Susceptible trees appear to be those growing on droughty, shallow soils, low in organic material; and those that are in a general decline. Affected branches can be pruned. Yard trees should he watered, mulched and fertilized periodically to increase their vigor.
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