The Department of Agriculture and Food, Western Ausgralia says Wheat Streak Mosaic Virus (WSMV) in-crop surveys have resulted in detections over a wide area of the wheat belt.

Principal plant virologist Roger Jones said WSMV had been found this spring from Esperance and Katanning districts in the south, Merredin and adjoining districts in the east and near Dongara in the north.

WSMV affected wheat

healthy wheat compared with WSMV affected wheat

WSMV is spread by means of infected wheat seed and a vector mite, the Wheat Curl Mite (Aceria tosichella).  It was first detected in autumn self-sown wheat and became apparent this season in wheat crops in WA for the first time. 

The symptoms appear as pale and green streaking on the leaves with yellowing of leaf tips and stunted and tufted growth.  The streaking is usually most obvious on older leaves towards their basal halvesd.

Dr Jones said that in most cases only scattered individual plants were showing the symptoms amidst a paddock of healthy wheat.

“In at least one instance there is 100% infection resulting in crop failure” he said.

“Excellent co-operation from agronomists and consultants has provided numerous samples as part of a WA Wheatbelt WSMV survey and the disease has now been detected over a large area.  Locations with positive detections to date include Dongara, Wongan Hills, Goomalling, Quairading, Kellerberrin, Koorda, Trayning, Burracoppin, Moorine Rock, Merredin, Hyden, Narembeen, Karlgarin, Corrigin, Nyabing, Lake King and the Esperance area (Gibson, Scadden, Yerritup),” Dr Jones said. 

“Agronomists also report seeing the characteristic symptoms in crops from which no samples have been tested, particularly in the Merredin area,” he said.

The Department of Agriculture and Food provides diagnostic services through AGWEST Plant Laboratories, and growers who suspect they may be seeing WSMV can send fresh samples for identification (chargeable).

Dr Jones said research indicated that dispersion through infected wheat seed stocks may account for the wide distribution of WSMV found in the 2006 growing season.

“It is important that seed from WSMV affected crops should not be retained for sowing.  Healthy seed is essential for WSMV management.  Farmers in affected areas should preferably source seed from low risk areas,” he said.

Dr Jones said a testing service for seed samples would be available for seed harvested in 2006.

“A seed test will help growers to evaluate the risk of establishing the disease from seed and sowing infected seed can be avoided if tests show a positive result,” he said.

Dr Jones said that a substantial ‘green bridge’ of volunteer cereals and grasses before the growing season favoured mite vectored infection of subsequent wheat crops.

“This is also the experience in New South Wales where more that 20,000 hectares are badly affected with WSMV this year.”

Dr Jones said the only known control options against WSMV were to control the ‘green bridge’, to sow healthy seed stocks of wheat, and to avoid early sowing when mild autumn temperatures favour the wheat curl mite vector. 

“Unfortunately, there is no effective miticide to spray against the vector, and there are no WSMV-resistant wheat varieties available.” Dr Jones said. 

For more information on WSMV and wheat curl mite refer to: NWS DPI - PrimeFact 99, WSMV and wheat curl mite