Wheat streak mosaic virus could be problematic this coming season, with rainfall and hail events around the state. One of the best preventative measures for wheat streak is the control of volunteer wheat early and often after harvest. If volunteer wheat is allowed to stand, it creates a “green bridge”, allowing wheat streak mosaic and wheat curl mites to survive locally. Volunteer wheat should be terminated at least two weeks prior to planting to allow sufficient time for mites to die off. Growers should be mindful of volunteer wheat that may “hide” in double-cropped soybeans or cover crops.
Breaking the “green bridge” - wheat curl mites will move off growing wheat as the green tissue dries down and dies. After moving off the existing wheat at or near harvest time, the mites need to find green tissue of a suitable host soon or they will die (death of the whole population will take approximately 2 weeks).
Management with genetic resistance - One tool in the toolbox, other than timely control of volunteer wheat, genetic resistance is also an important tool for WSMV control. Genetic resistance to wheat streak mosaic can also reduce the risk of severe disease problems. There are currently several that have wheat streak mosaic resistance.
Some of these varieties have a gene named WSM2. These resistance genes help but have some serious limitations. For example, they are effective against wheat streak mosaic virus, but not against triticum mosaic or wheat mosaic virus (high plains disease), two other viral diseases spread by wheat curl mites, sometimes simultaneously. The resistance conferred by WSM2 is also temperature sensitive and is much less effective at high temperatures
Although resistance in a few varieties seem to endure greater temperatures before breaking down (~ 70º F). If wheat is planted early for grazing or if high temperatures persist into October, the resistance is much less effective.
In addition, there are a handful of varieties with resistance to the wheat curl mite. These varieties remain susceptible to viral diseases, but they generally slow the development of the mite populations in the fall. This resistance can help reduce the risk of severe disease but will not provide enough protection if wheat is planted in close proximity to volunteer wheat or other hosts infested with large populations of the curl mites and virus.
Unfortunately, many of these varieties are adapted to Western Kansas and may not be the best options for production systems in the central corridor. There are some central Kansas-adapted varieties that tolerate WSMV infection better than others. These varieties will still show symptoms of WSMV, but may yield better than other varieties that are more susceptible.
More information on variety selection can be found at www.cottonwood.ksu.edu click onto the Crops and Livestock tab and look under Hot Topics. Also the full version of this abbreviated article is listed there too.
Other hosts for the wheat curl mite -volunteer wheat is not the only host of the wheat curl mite. Over the years, multiple research studies have evaluated the suitability of wild grasses as hosts for both the curl mite and the wheat streak virus. The K-State Research and Extension publication, MF3383 - Wheat Streak Mosaic, includes information about grassy weed hosts of the mite and virus, and the contribution of these hosts to the risk of severe wheat streak mosaic infections. Take note of significant stands of these grasses in marginal areas and control them as you would volunteer wheat.
If volunteer wheat and other hosts are not controlled throughout the summer and become infested with wheat curl mites, the mites will survive until fall and could infest newly planted wheat. Wheat curl mite infestations of wheat often lead to wheat streak mosaic infections.
Stacy Campbell is an agriculture and natural resources agent for Cottonwood Extension District. Email him at scampbel@ksu.edu or call the Hays office, 785-628-9430.
