Weed control this fall could prevent devastating disease next year

By: 
DARREN CRAWFORD
Fergus Co. Extension Agent

As we enter the Labor Day weekend and the weather starts to feel more like fall, area farmers are starting to think about next year. Thick stands, new crops, ample rain and hopefully better prices are filling their dreams. But along with those dreams, there are some nightmares as well; such as a bad infestation of Wheat Streak Mosaic Virus.

Wheat Streak Mosaic Virus is a disease that can have a devastating effect on wheat crops, especially when the crop is infected at a young stage. The virus is spread by the Wheat Curl Mite, being carried from plant to plant by these tiny insects as they feed. The mites themselves don’t do much damage. They are very tiny, only able to be seen with a hand lens or a microscope, but the diseases they can introduce to a new wheat plant can have a huge impact on crop production.

There is no cure for WSMV, but there are actions we can take to prevent it. The primary management technique for preventing WSMV is to eliminate the “green bridge” before planting the next crop. This means killing all host plants in the field to be planted and any adjacent fields. This can be accomplished through herbicides or tillage, but we often have to wait until grassy weeds and volunteer wheat has germinated and started growing. The best management practice to avoid WSMV is to kill all vegetation, then wait two weeks before planting winter wheat this fall. The Wheat Curl Mites cannot survive very long without green plants in a field and will dry up and die quickly once their host plants have been killed and they can’t find a neighboring host plant on which to live.

Eliminating the green bridge is important every year, but following a year with widespread hail damage it is imperative to be diligent in our efforts. Hail damage on a mature crop scatters seeds and creates a huge crop of volunteer wheat plants. Hail damage on earlier stages of wheat often results in plants that had some re-growth that makes a small amount of seed that is not harvestable, and ends up falling to the ground to make new volunteer wheat plants. These volunteer plants and grassy weeds such as cheat grass provide the habitat for the wheat curl mite to survive to infest the next year’s crop, carrying the WSMV with them. Killing these plants and waiting two weeks may mean some delayed planting dates for this fall, but the penalties for delayed planting are much less than the penalties for a severe WSMV infection.

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