Diseases of... Conifer Foliage

Common Name:

BROWNSPOT NEEDLE BLIGHT

Grass stage longleaf pine seedling severely damaged by brown spot needle blight.

Pathogens:

Fungus Scirrhia acicola

Common Host:

Longleaf pine Pinus palustris

Significance:

Brown spot needle blight is regarded as the most serious disease affecting longleaf pine. Young, grass stage seedlings are particularly vulnerable to severe infections and may die as a result. More commonly, however, infected grass stage seedlings are stunted and grow poorly for years until they are able to outgrow the influence of the disease. Other pines and older trees, may be infected with the brown spot fungus, but the resulting infections are of little consequence.

Recognition:

Typical symptoms of this disease include small (3 mm) spots on needles that vary in color from straw yellow to light brown to brown with distinct purple or amber-yellow margins. Infected needles are often green at the base, dead (brown) at the needle tip, and mottled with spots separated by definitive bands of green tissue in the middle. As needles die, they may appear to have been scorched by the heat of a fire. It is common for needles killed by brown spot needle blight to assume an embossed appearance since the live green bands of tissue often shrink more upon the death of the needles than do the symptomatic brown spots. In certain cases, brown spot symptoms and symptoms caused by certain needle cast fungi (esp. Lophodermium spp.) are identical and only laboratory analyses can be relied upon for specific diagnoses.

Infection Biology:

Spores of brown spot fungus are produced in two types of small (less than 1 mm), black fruiting bodies on symptomatic needles. These spores (called conida and ascospores) are liberated and spread by wind and rain. New infections may occur on longleaf pine throughout the year, but most infections occur between May and October.

Control:

Brown spot needle blight can be effectively controlled in nursery and ornamental environments with carefully applied fungicidal sprays. In commercial forest situations the use of genetically resistant planting stock is recommended. Perhaps the most effective control for this disease in commercial forestry is the use of prescribed burns. Well time (January - February) and carefully controlled fires destroy infected needles along with the brown spot fungus, thereby reducing the source of fungus inoculum as well as new infections. Although needles are scorched by fire, vigorous grass stage seedlings with root collars 1 or more centimeters in diameter are particularly fire resistant, and able to survive quite well. Controlled burns may also be useful as a sanitation or eradication measure before planting longleaf seedlings in previously infected areas.

Typical brown spots on needles of longleaf pine resulting from infection by Scirrhia acicola.

Fig. 11. Natural range of longleaf pine in Florida (green) and distribution of brown spot needle blight (striped). (Source: U.S. Forest Service)

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Bulletin No. 196-A | Printed October, 1983 | Contact the Forest Health Section

Florida Department of Agriculture and Consumer Services