[Illustration: Galls on 1-0 pine nursery stock.]
[Illustration: Damage caused by fusiform rust infection.]
Fusiform rust, caused by _Cronartium fusiforme_, is one of the most
important diseases on southern pines. This rust is found from Maryland
to Florida and west to Texas and southern Arkansas. The rust’s most
important impact is in nurseries, seed orchards, and young plantations.
Loblolly and slash pines are very susceptible to this rust. Pitch and
pond pines are moderately susceptible, longleaf pine is fairly
resistant, and shortleaf pine is highly resistant.
The most easily recognized symptom is the spindle-shaped canker on the
pine branches or main stem. In early spring these swellings appear
yellow to orange as the fungus produces powdery spores. As host tissue
is killed, older stem cankers may become flat or sunken. Cankers often
girdle trees and wind breakage at the canker is common. Fungus spores
from the pine infect oak leaves. Brown hair-like structures, produced on
the underside of the leaves in late spring, are the most conspicuous
signs. These projections produce spores which in turn reinfect the pine
trees, completing a “typical” rust cycle.
[Illustration: Fruiting fusiform-shaped canker on main stem of
southern pine.]
Silvicultural practices may lessen the incidence of infection in
plantations. Avoid planting highly susceptible species such as slash and
loblolly pines in areas of known high rust incidence. In these areas
more resistant species such as longleaf or shortleaf pine should be
planted. Pruning infected branches will prevent stem infection in young
plantations. Rust-resistant pines should be readily available from the
nurseries in the near future. Culling out seedlings with obvious galls
before outplanting will reduce the disease incidence in new plantations.