Brown spot or brown spot needle blight is caused by the fungus _Scirrhia
acicola_. Brown spot occurs in all the coastal states from Virginia to
Texas, and inland to Arkansas and Tennessee. All southern pines are
attacked by the fungus, but only longleaf pine seedlings are seriously
damaged.
[Illustration: Brown spot needle blight on longleaf pine
reproduction.]
Initial infection of pine needles results in the development of small,
circular spots of grey green color, which later turn brown. As the
fungus continues to grow, a necrotic area encircles the needle,
appearing as a brown band. The infected area will then increase in size,
eventually resulting in the death of the needle. Fruiting bodies, called
acervuli, develop in the dead areas of the needle. Spores are extruded
from the acervuli in a water soluble gelatinuous matrix throughout the
entire year. The spores are washed apart and splashed short distances by
rain drops. These spores spread the disease from seedling to seedling.
During the winter and early spring, the sexual stage of the fungus is
produced on dead needles. Ascospores, produced in a fruiting body called
a perithecium, are light and wind-disseminated. These spores are
responsible for disease spread. During the grass stage, seedlings often
become heavily infected by the brown spot fungus, resulting in partial
to complete defoliation. Seedlings which are nearly defoliated every
year remain in the grass stage and eventually die. Three successive
years of complete defoliation will result in death. The disease is very
damaging during wet years, especially in areas where the fungus has
become well established in the absence of controls.
The disease can be reduced by control burning during the winter months.
On seedlings, fire burns the diseased needles and reduces the amount of
available inoculum for reinfection, leaving the large terminal bud
unharmed. Often a single prescribed burn reduces the disease intensity
to such low levels that vigorous seedling height growth begins the
following year. Fungicide sprays will also reduce brown spot on high
valued trees.