Ornamental & Tree Diseases
Brown Spot Needle Blight
Brown spot needle blight is a fungus-caused (Mycosphaerella dearnessii = Lecanosticta acicola) disease that occurs in all coastal states from Virginia to Texas and inland to Arkansas and Tennessee. All Southern yellow pines are attacked by the fungus, but only longleaf pine seedlings are seriously damaged. In the absence of disease management, seedlings are frequently infected in the grass stage. Repeated defoliations often results in death. The brown spot needle blight fungus is also responsible for significant losses in Scotch pine Christmas tree plantations throughout the midwestern and north-central states.
This fungus overwinters as mycelium, acervuli, and perithecia in infected needles. Beginning in early April, the fungus produces two types of spores in abundance during moist periods. They include greenish-brown, curved, one- to three-celled conidia from acervuli that are disseminated by splashing rain, and oblong, bicellular ascospores from perithecia, which are disseminated by wind. Hyphal strands from germinated spores penetrate needle tissues by growing through open stomata. Subsequent growth and development of the brown spot needle blight fungus in needle tissues cause death of mesophyll cells, resulting in characteristic symptoms.
Infected areas on needles initially appear as Brown Spot surrounded by yellow bands. Fungal growth in infected tissues is accompanied by enlargement of spots that frequently merge, resulting in death or blight of entire needles. Within 2 to 8 weeks after infection, the fungus produces acervuli and perithecia within infected tissues, which provide secondary inoculum throughout the year.
Management recommendations include:
1. Excluding the pathogen by planting only disease-free seedlings in regeneration areas.
2. Eradicating or reducing the pathogen by prescribed burning in young natural stands or plantations of longleaf pine that are still in the grass stage. Burning in established stands during the dormant period is recommended if infection exceeds 20 percent.
3. The application of recommended protective fungicides is widely used in nurseries.
4. Planting genetically resistant selections of longleaf pine. Limited supplies are becoming available.