Net blotch (NB) is common throughout NZ, caused by the fungus Drechslera dictyoides, usually in autumn and winter. NB can seriously affect winter pasture.
Perennial ryegrass, tall fescue.
NB produces a fine network of short brown streaks on the underside of leaves. These later turn into dark brown, solid spots. In heavily infected plants, leaf tips will yellow and die back, imitating N deficiency. NB is more severe in long dense swards.
NB is spread on wind-borne spores produced by lesions. The fungus survives on infected stubble. Wet, humid weather favours NB spread.
Prevention and management
Graze pasture before it becomes long and rank to reduce the chance of NB and lower severity of the disease. Under severe infection, fungicides may be economical
Net blotch on ryegrass leaves.