Rhizosphaera Needle Cast

Rhizosphaera needle cast is the most common disease on spruce trees that is received in the Plant and Insect Diagnostic Clinic. Rhizosphaera needle cast is caused by fungal pathogens within the genus Rhizosphaera. This genus also infects several conifer species including; fir, cedar, spruce, and pine

Oak Wilt

Oak wilt is a serious disease that can infect many oak species. It is caused by the fungus, Ceratocystis fagacearum. Red oaks are very susceptible to the oak wilt fungus and can die within 4-6 weeks.  White and bur oaks are susceptible, but the symptoms develop slowly. Trees can be infected by the fungus through root grafts or by beetle vectors that carry spores to newly wounded trees. When a tree is infected it tree tries to protect itself by producing gummy material called tyloses which can clog the water conducting vessels. Water is prevented from moving to the canopy and leaves begin to wilt. Leaves of infected oaks can wilt, turn brown at the edges, and fall off. The outermost ring of sapwood sometimes turns brown and appears as streaks when the bark is peeled; or as a ring when the branch is cut in cross-section. Because oak wilt is often confused with other disorders, positive identification requires recovery of the causal fungus from the tree.

Dothistroma Needle Blight

Dothistroma needle blight is especially common on Austrian pines.

Diplodia Tip Blight and Canker

Diplodia tip blight is caused by the fungus Sphaeropsis sapinea.

Corn Smut


Corn smut is caused by the fungus ustilago maydis. When severe, the infection can impact the number and quality of corn ears. While forms of resistance are bred into many modern corn cultivars, heirloom and landrace varieties are incredibly susceptible to the fungus. Therefore, any home gardener should be aware of the threat of corn smut when selecting varieties.

Black Knot

This disease is caused by the fungus Apiosporina morbosa and typically affects both wild and cultivated cherry, chokecherry, and plum species. Black cherry and pin cherry are not susceptible to black knot.