Western Australian cereal growers are being urged to destroy ‘green bridge’ cereals and grasses prior to sowing where they are at risk of disease threat by wheat streak mosaic virus.

Department of Agriculture and Food virologist Roger Jones said removing the ‘green bridge’ at least four weeks before sowing so that no grass plants were still surviving was the most effective means of limiting the impact of the disease.

He said growers should also not sow seed that has been saved from conspicuously infected crops and, in high risk situations, could delay sowing to avoid seedlings emerging in warm conditions that favoured greater vector mite activity.

Close up of wheat plants affected by wheat streak mosaic virus.

Dr Jones will update agribusiness and research leaders at the Department’s annual Agribusiness Crop Updates on 14-15 February, supported by the Grains Research and Development Corporation.

“Following the detection of wheat streak mosaic virus in the Merredin district in August 2006, the Department undertook an extensive survey of wheat crops and trials throughout the grainbelt,” Dr Jones said.

In the survey of wheat trials involving 4,016 samples, wheat streak mosaic virus was detected on 9 of 23 farms and in 13 of 44 trials.

In the survey of commercial crops, 7,630 random samples were tested and infection was found on 19 of 27 farms and in 27 of 75 crops.

“The virus was detected in many different wheat varieties in crops and trials at sites over a very wide area in all rainfall zones ranging from Esperance in the south to Dongara in the north,” Dr Jones said.

“However, infected sites were concentrated particularly in the eastern grainbelt districts that received considerable summer and autumn rains.”

Dr Jones said this distribution of infected sites indicated that a substantial ‘green bridge’ before the growing season favoured high infection in following wheat crops.

He said the virus was detected in alternative hosts including volunteer wheat, barley, annual ryegrass, barley grass, windmill grass and wild oats.

“Examples particularly from the Merredin district indicated that, where this ‘green bridge’ was not adequately controlled, major crop loss could result,” he said.

A seed testing service for seed samples sent in by growers will be available from AGWEST Plant Laboratories from February 2007.