Health Protection, Southern Region
caused by Cronartium quercuum f. sp. fusiforme
Importance. - Fusiform rust infections that occur on the main stem within the first 5 years of a tree's life normally cause tree death. Infections
that occur later in the life cycle of the tree weaken the stem, resulting in wind breakage at the canker or quality loss at rotation. Losses in individual nurseries can
exceed 80 percent. Loblolly and slash pine are the most susceptible species. Longleaf is fairly resistant, while shortleaf pine is highly resistant. Oak is the
Identifying the Fungus. - The fungus produces orange spores on the surface of fusiform-shaped pine galls in the spring. Orange spores
are produced on the lower surface of the oak leaves. Later, hairlike structures are also produced on the leaf.
Identifyingthe Injury. - Spindle-shaped swellings or galls develop on the branches or main stem. Main stem infections on older trees
are somewhat depressed on one side. Trees commonly break at the canker. In the spring, the galls turn orange. Infection on the oak host produces orange
leaf spots and hairlike telia, which can cause cupping and curling of the leaf.
Fusiform rust fruiting
on loblolly pine. (Click for detail. JPG 33K)
Fusiform rust damage to
main stem. (Click for detail. JPG 45K)
Biology. - Orange-yellow blisters form on the pine gall: the blisters produce aeciospores. In late spring, uredia are formed on the
underside of young oak leaves. During late spring or early summer, brown, hairlike structures (telia) form on the oak leaves. Spores produced on the telia
infect the pine.
Control. - The control strategies for fusiform rust are complex for forest stands and nurseries, and are too numerous to discuss
here. The user is referred to the Integrated Pest Management Decision Key (IPM-DK) for more information. Discuss this with a State or Federal forest
pest management specialist.