Sampling ryegrass to assess the risk of annual ryegrass toxicity

Most stock losses caused by annual ryegrass toxicity occur because stockowners unknowingly allow their stock to graze annual ryegrass (Lolium rigidum) infected with the bacterium Clavibacter toxicus. To help stockowners avoid losses we have developed criteria for a testing service to determine the risk of poisoning before the pasture is grazed. Low, medium and high risk categories were selected using samples of dry, mature ryegrass seedheads collected by stockowners from untreated, infected pastures in South Australia. The proportion of toxic paddocks in each risk category over all the seasons tested was 11%, 32% and 76%, respectively, and these accounted for 7%, 14% and 79% of total stock losses. The proportion of paddocks in which stock were poisoned did not vary significantly between years, was not affected by variation in sample weight, and did not vary between South Australia and Western Australia.