By STACY CAMPBELL
Cottonwood Extension District
During this past season, we have seen widespread wheat streak mosaic virus across the state. Because of this, abundant curl mites will be active in the state. Producers should be vigilant about volunteer management between now and planting. Recent moisture may lead to higher levels of volunteer wheat emergence in the coming weeks.
Volunteer wheat control is one of the most important preventative measures for wheat streak mosaic virus. 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 before 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 and may be difficult to control.
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).
Producers often like to wait several weeks after harvest before making their first herbicide application to control volunteer wheat. This allows as much volunteer wheat as possible to emerge before spraying it or tilling it the first time. Glyphosate and atrazine are two herbicides that are often used for this purpose. Additional information about controlling volunteer wheat can be found in a recent eUpdate article: “Controlling weeds after wheat harvest.” Often, a second application or tillage operation will be needed later in the summer to eliminate the green bridge to fall-planted wheat by ensuring all volunteer wheat is dead within ½ mile of wheat being planted in the fall. Wet weather through late summer often favors multiple flushes of volunteer wheat. Also, it favors the growth of other grassy weeds that can support moderate populations of the curl mites and virus.
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 wheat varieties adapted to Kansas that have wheat streak mosaic resistance. To see these refer to the full text of this article in the K-State Agronomy eUpdate, by typing that into your internet browser.
More information on variety selection can be found here: MF991 KS. Wheat Variety Guide https://bookstore.ksre.ksu.edu/pubs/kansas-wheat-variety-guide-2023_MF991.pdf
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. There is considerable range in the ability of a grassy weed species to host the mite and the virus. Barnyardgrass is among the more suitable hosts for both the virus and mites, but fortunately, it is not that common in wheat fields. In contrast, although relatively poor hosts, various foxtails could be important disease reservoirs simply because of their abundance. These grasses may play an important role in allowing the mites and the virus to survive during the summer months, particularly in the absence of volunteer wheat.
The K-State Research and Extension publication, MF3383 - Wheat Streak Mosaic, includes information about grassy weed hosts of the mite and the 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.
Information provided by Kelsey Andersen Onofre, Romulo Lollato, J.P. Michaud, and Sarah Lancaster K-State Extension Specialists.