BROWN RUST
SYMPTOMS
Brown rust is mainly a disease of the leaf.
The earliest symptoms are small, elongated yellowish
spots that are visible on both leaf surfaces. The spots
increase in length, turn brown to orange-brown or
red-brown in color, and develop a slight, but definite,
chlorotic halo (Figure 1). Lesions typically range
from 2-10 mm in length but occasionally reach 30
mm. They are seldom more than 1-3 mm in width.
Infections are usually most numerous toward the leaf
tip, becoming less numerous toward the base.
Pustules, which produce spores, usually develop on
the lower leaf surface (Figure 2). Certain cultivars,
however, may have some pustules on the upper
surface. Pustules may remain active over a considerable
period of time and spore production is highly
dependent upon climatic conditions. However,
eventually lesions darken and the surrounding leaf
tissues become necrotic.
On a highly susceptible variety, considerable
numbers of pustules may occur on a leaf, coalescing
to form large, irregular, necrotic areas. High rust
severities may result in premature death of even
young leaves. Severe rust has caused reductions in
both stalk mass and stalk numbers, thereby reducing
cane tonnage.
