Net blotch (NB) is common throughout NZ, caused by the fungus Drechslera dictyoides, usually in autumn and winter. NB can seriously affect winter pasture.

 

Species affected

Perennial ryegrass, tall fescue.

 

Identification

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.

 

Spread

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.