In early spring a bright orange powder often appears on pine trees. This powder is actually spores from a disease called “Fusiform Rust,” and it attracts attention to a particular area of a pine tree that is usually misshaped or swollen.

The orange spores are only produced in the spring, but the infected portion of the tree will grow throughout the year. Fusiform rust will cause individual branches to have an elongated swelling at the site of infection. Infection can also occur on the trunk of a tree causing cankers.

Severe trunk infections can weaken the tree structure. Trees that have severe trunk infections and are near structures may need to be removed. Individual limbs can be pruned without damaging the tree.

Fusiform rust is most damaging to slash and loblolly pines. The rust can infect longleaf pines to a lesser degree. Trees may have more than one area infected with fusiform rust, but each infection is separate. The disease is not translocated throughout the tree, but infections on limbs near the trunk can grow into the trunk.

The orange spores you see on pine trees are not the spores that infect pine trees. These orange spores actually infect oak trees which in turn produce spores capable of infecting pine trees. Water, willow, laurel, southern red, and several other types of oaks are part of the life cycle of fusiform rust.

Unlike pines, the fusiform rust disease does little or no harm to oaks. Infected oaks may have faint leaf spots on the leaves. Infected oak leaves develop brown, hair-like bristles on the undersides of their leaves. These bristles contain microscopic spores that are released in late spring.

The spores are carried by the wind to susceptible pines. The spores germinate and the fungus begins its growth. The entire cycle from orange spores on pines to infecting oaks that produce spores that infect pines only takes a few weeks each spring. Pines are infected in April or May.

There is no cure for pines once they contract fusiform rust disease. Seedling pines that are infected should be removed. Fusiform rust causes millions of dollars of damage to commercial pine stands each year.

Pine stands that are sparsely stocked are infected at higher rates than densely stocked stands. This seems in contrast to how many fungal diseases operate. The disease is also more of a problem when young trees grow rapidly.

Infections on limbs that are within 15 inches of the trunk should be removed so the infection will not enter the trunk. Do not try to cut out trunk infections because it will be very difficult to remove all the diseased tissue without causing structural damage to the tree.