Net Blotch of Barley

Lesions first appear as tiny spots that may be dark green and water soaked initially but turn to light brown as they mature. Symptoms later 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 the disease is severe, the lesions spread over the entire leaf and kill it. Lesions may occur on the spikes as the crop matures.

Net blotch of barley affects only domestic and wild barleys (Hordeum spp.). The fungus survives between growing seasons on barley residue, volunteer barley plants, some grasses, and seed. Barley residue and volunteer barley plants are the main sources of inoculum 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. Humid and cool spring weather favor disease development.

To control this disease, rotate to a crop other than barley and reduce residue by harvesting straw and incorporating stubble. Destroy volunteer barley and grass hosts. Avoid early plantings (October to November) in known infested fields because when conditions favor disease development, late plantings (December to January) are less damaged. Use clean seed and resistant cultivars (see barley cultivar information).