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

 

Species affected

Perennial ryegrass, tall fescue.

 

Identification

NB produces a network of short dark brown bars which run across the leaf blades. These enlarge and become dark brown, solid spots. In heavily infected plants, leaf tips yellow and die back. NB is more severe in long dense swards in moist conditions.

 

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. Apply N based fertiliser after grazing to boost regrowth and reduce the incidence of NB. Under severe infection, fungicides may be economical.

 

Making silage will not remove NB; Instead, it will make the silage less palatable.

 

 

Net blotch on ryegrass leaves.