Wheat streak mosaic virus
- Southern Cross
Gary Kenward (Yilgarn Agencies) has reported wheat streak mosaic virus (WSMV) in wheat crops at Southern Cross. The wheat varieties infected are Mace, Magenta, Zen, Harper plus an admixture of Spear and other varieties. The paddock worst affected is the admixture paddock. The plants are at ear emergence (Zadok 57).
Wheat streak mosaic virus (WSMV) is seed-borne and spread by wheat curl mite (WCM). The WCM requires warm conditions to build up (23-28°C), and populations decrease quickly with cold temperatures. A gradient of infected (yellow) plants can often be seen across a wheat crop with the highest concentration of infected plants being near the volunteer wheat green bridge and diminishing with distance into the crop. Early infection (pre-flowering) can cause yield losses and shrivelled grain but infection after flowering has little effect on yield or seed quality. Growers should consider destroying infected crops this season to reduce potential for infected seed to germinate next year.
There is no effective miticide to spray against the disease vector, wheat curl mite (WCM), and there are no WSMV-resistant wheat varieties in Australia. Management of the disease is highly dependent on reducing sources of WSMV and limiting build-up of WCM populations. Seed transmission of WSMV is known to occur at low levels (<1%) and is one of the contributing factors for the carry-over of virus between seasons. Seed infected with even very low levels of the virus can cause significant yield losses as infection is able to take hold early in the season. Seed being kept for sowing next year should come from WSMV free crops. DDLS - Plant pathology services can test seed lots for the presence of WSMV.
Destruction of volunteer cereal or grass host plants (green bridge) prior to sowing wheat is the best method of preventing WSMV transmission. These green bridge hosts act as a reservoir of infection and build-up the population of the WCM vector. This control needs to be done throughout the paddock (including along the fenceline) at least one month before sowing wheat. It needs to be very thorough, involving grazing down to ground level throughout the paddock or early application of herbicide. Neighbouring paddocks should be treated similarly, especially those upwind of the crop. This will ensure the emerging crops are not exposed to early WSMV infection. There are no management options once transmission into a wheat crop has occurred.
For more information contact Brenda Coutts, Plant Virologist, South Perth on +61 (0)8 9368 3266.