Fusiform rust

Natural History
Fusiform rust gall
Photo credit: G. Blakeslee - SFRC, Univ. of Florida

Fusiform rust is a disease caused by a fungus. This disease deforms or kills pine trees throughout the South, including north Florida. Since the late 1950s and early 1960s, fusiform rust has caused extensive damage in slash and loblolly pine plantations. The disease is estimated to cause many millions of dollars in losses in Florida each year.

The fungus requires two living host trees, pine and oak, to complete its life cycle. The fungus cannot spread directly from pine to pine. Young oak leaves are infected in the spring by wind-borne spores produced on pine trees. The fungus does minimal damage to the oak leaves, but later in the spring wind-borne spores produced on the young oak leaves infect new pine growth. The fungus can stunt, deform, or kill pine trees. In many cases, the fungus weakens the tree causing branches to be easily broken off or the whole tree to be blown over by wind.

Two common, interesting symptoms of fusiform rust are galls and witches' brooms. Galls are abnormal growths and swellings that can be found on nearly every part of a plant. Galls can be caused by a variety of organisms including bacteria, fungi, nematodes, wasps, and mites. Fusiform rust often causes galls on the branches or main stem of pine trees.

A witch's broom occurs when a compact cluster of numerous twigs and branches shoots out from a common point, giving that section of the plant a broom-like appearance. Fusiform rust is just one of many factors that can create a witch's broom. This symptom can also result from various other sources including certain insects and diseases.


Identifying Characteristics

Identifying the disease: Infected pine trees bear spindle-shaped branch galls that, in the spring, are covered with yellow-orange blisters called "aecia." Infected oak leaves bear brown, fuzzy patches of fungus composed of hairlike structures called "telia." The spores that infect pine trees come from the telia and the spores that infect oak come from the aecia.
Susceptible trees: Of the commercially important pine species, slash, loblolly, and longleaf pines are susceptible. Over 20 of the southern oaks including water, laurel, willow, and southern red oak can be infected.



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