According to University of Illinois plant pathologist Carl Bradley, wheat leaves displaying symptoms of virus infection, such as purple and yellow leaf tips or mosaic symptoms, have been observed in fields across the state.
Viruses of wheat are not uncommon in Illinois. Barley yellow dwarf virus (BYDV) is one of the most frequently observed viruses in past years (Figure 1). BYDV is transmitted by aphids that feed on wheat during the fall and spring months. Infections that take place in the fall generally cause more severe symptoms, such as stunting, while spring infections often cause discoloration of the leaves, especially on the tips.
Other common viruses include Wheat soilborne mosaic virus (WSBMV) (Figure 2) and Wheat spindle streak mosaic virus (WSSMV). Both of these viruses are transmitted by a soilborne organism that infects wheat roots, Polymyxa graminis, which can survive in the soil for many years. Symptoms of these two viruses appear as mottling and mosaic yellow patterns on leaves as well as stunting in severe cases.
“For WSBMV and WSSMV, continued development of symptoms to upper leaves often stops when temperatures warm up,” said Bradley. Preliminary results from a wheat virus survey conducted in Illinois from 2009 to 2011 indicate that other viruses also may be found in Illinois wheat fields, such as Wheat streak mosaic virus and High plains virus.
In general, diagnosing viral diseases can be very difficult. ”Going only by symptoms to diagnose viruses often will result in a misdiagnosis,” said Bradley. To ensure proper diagnosis, it is important that affected plant samples be sent to a lab that will run assays that specifically test for viruses, such as ELISA or PCR.
The U of I Plant Clinic (http://web.extension.illinois.edu/plantclinic/) does not run these virus-specific tests for wheat, but can help facilitate virus testing through Agdia (www.agdia.com). Wheat samples for virus testing can be sent to the Plant Clinic or directly to Agdia (see Agdia’s website for specific information).
There are no in-season control options for wheat viruses once symptoms are being observed. For viruses transmitted by aphids, insecticide seed treatments and foliar insecticides can be used to prevent transmission of these viruses.
“For the best management of wheat viruses, choose varieties that have high levels of resistance to these diseases,” said Bradley.