Cotton leaf rust
Cotton leaf rust or southwestern rust is caused by the fungus Puccinia cacabata. The aecial stage of the rust occurs on cotton and causes bright yellow to orange spots on the leaves, bracts and bolls during the summer rainy season. P. cacabata also infects several species of grama grass which are the alternate hosts for the fungus. Teliospores, the over-wintering stage of the fungus, are produced on grama grasses. During summer rains, teliospores germinate and produce basidiospores that infect only cotton. Since the repeating stage (urediniospores) of this rust occurs on grama grasses, infections of cotton occur only after spore showers originate from infected grama grasses. Disease is erratic because it is so dependent on moisture, but can be prevented by protective applications of mancozeb fungicide.
