Producers are being urged to check their grass leys for leaf spot as high levels have been seen in NIAB TAG variety and grazing trials.
NIAB TAG warned if unchecked, the fungal disease Drechslera leaf spot, could results in a reduction in the quality and value of late season grazing.
Trials manager Peter Burgis in Yorkshire said he has seen over 40% leaf area infected with the disease in variety plots, and significant levels of the disease in on-farm grazing trials.
“Cattle are rejecting the badly infected varieties, which leads to excessive growth and more disease build-up. Drechslera leaf spot can persist in cold weather leading to further winter damage. Infected material needs to be topped, or grazed more tightly with sheep before going into the winter,” he added.
There are several different species of Drechslera which can infect perennial ryegrasses, and typical symptoms include brown spots surrounded by yellowing tissues, or in some cases distinct brown netting lesions similar to those caused by net blotch on barley.
NIAB TAG pathologist Dr Jane Thomas added: “The disease can appear quite insignificant, though just one or two spots will often kill the entire leaf. However, when the disease increases to produce a widespread blight, the effects on the sward can be dramatic.”
She said susceptible grass varieties would need “appropriate management” and advised using them in mixtures with more resistant types to avoid serious infections.
Livestock producers looking for more information on the resistance of perennial ryegrass varieties, can get some from seed merchants contributing to the Grass Levy Scheme, which is supported by BSPB, EBLEX and DairyCo.