Scald is common disease of barley in temperate regions. It is caused by the fungus Rhynchosporium secalis and can cause significant yield losses in cooler, wet seasons.
Scald is a foliar disease of barley affecting the leaves and sheaths of the plant; however, lesions may also occur on coleoptiles, glumes, floral bracts and awns. Initial symptoms are oval, water-soaked, grayish-green spots, 1.0-1.5 cm long. As the disease develops, the centers of the lesions dry and bleach, becoming light gray, tan, or white with a dark brown margin. The lesions are not delimited by the leaf veins and often coalesce.
The fungus can infect and survive in barley seed. It exists as mycelium in the pericarp and hull of infected seeds. Infection of the coleoptile occurs as it emerges from the embryo. Optimal infections occur at soil temperatures of 16C. At soil temperatures of 22C or higher, very little infection occurs.
In spring cropping systems, the fungus overwinters on the crop debris and stubble of previous diseased barley crops. The fungus produces abundant conidia on wet lesions during cool, damp weather after the leaf tissue has become necrotic. Conidia, spread by wind and splashing rain, infect young leaves of spring- planted grain. Optimum temperatures for sporulation and infection range from 10-18C. Hot, dry weather reduces the rate of disease development.