Importance. -- In forest stands these diseases are of minor importance
on oak (alternate host). However, they affect the aesthetic value of
shade trees and ornamentals. Fusiform rust on pine (primary host) is
the most important disease of pine in the Southeast, while eastern gall
rust is generally a minor pest.
the Fungi (figure 70). --
Both fungi develop brown, bristly spine-like structures on the underside
of the oak leaf.
the Injury. --
Small yellow spots develop on the leaf surfaces in spring. Some defoliation
may occur. Red, water and willow oaks are primarily affected. White
oaks are seldom affected.
Leaf rusts require two hosts to complete their life cycle. Fungus spores
(aeciospores) produced on pine galls are windblown and infect young
oak leaves. Spores (urediospores) are produced on the oak leaf which
reinfect oak. Spiny-like hairs (telial columns) on the lower oak leaf
surface release teliospores which produce another spore stage (basidiospore)
that infects pine. This infection results in a gall with aeciospores,
and the cycle is completed.
No control needed on oaks as the damage is minor.