Insects and Diseases of Trees in the South

by Anonymous

SEPTORIA CANKER

Septoria canker on young cottonwood saplings.

Septoria canker is caused by the fungus Septoria musiva. Although this is a disease of poplars, native poplar species are not severely attacked. However, this is an important problem wherever hybrid or introduced poplars are grown. With the ever-increasing emphasis on poplar planting, this will probably become a much more important problem in the near future.

Young stem cankers usually develop around openings such as wounds, lenticels, or leaf scars, appearing first as sunken, dark areas of the bark. The infected area later becomes more depressed and darker as tissue dies, and often a black margin will be formed around the canker. Small, pink, hair-like spore tendrils are produced by the fungus around the canker margin, especially during moist weather. These tendrils contain spores which can cause further infection, and arise from small dark fungal fruiting structures called pycnidia. This cankered area is often invaded by insects and other fungi and is also a weakened area at which wind breakage may occur. The fungus also causes a gray to black leaf spot, which usually has a light colored center. These spots may coalesce on a severely infected leaf and involve the entire leaf surface. This leaf spot in itself causes slight damage, but acts as a source of fungus spores which can cause stem cankers, and thus is important in the overall consideration of the disease.

Defoliation in cottonwood caused by Septoria leafspot.

A control for this disease is to use native poplars or resistant hybrids wherever possible. Wider spacing in plantations may also reduce the humidity, decreasing the amount of infection.