Symptoms and Signs
Lesions first appear as tiny spots that may be dark green and water soaked initially, but turn light brown as they mature. Later, symptoms appear as narrow brown blotches with a netted or cross-hatched appearance. Surrounding tissue becomes yellow. In advanced stages a series of stripes with irregular margins extend in a parallel direction, sometimes the length of the leaf. When disease is severe, the lesions spread over the entire leaf and kill it. Lesions may occur on the spikes as the crop matures.
Comments on the Disease
Net blotch of barley affects only domestic and wild barleys (Hordeum spp.). The fungus survives between seasons on barley residue, volunteer barley plants, some grasses, and seed. Barley residue and volunteer barley plants are the main sources for new infections each season. After initial infections, spores are produced on lesions when humidity is near 100% and temperatures are mild, 60° to 80°F (16° to 27°C). Spores are windblown to other plants for secondary spread. If infected seeds are planted, coleoptiles can be infected after the seeds germinate. Free moisture and cool spring weather favor disease development.
Primary control measures include crop rotation (to any crop other than barley), removal or disposal of barley residue from the surface of the soil, and destruction of volunteer barley and grass hosts. Also, avoid early plantings (Oct. to Nov.) because when conditions favor disease development late plantings (Dec. to Jan.) are less damaged. Use clean seed and resistant cultivars (see BARLEY CULTIVAR TABLE).