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Small Grains Disease and Pest Update 06/17/23

 The small grains crop scouts continued to find grasshoppers and aphids this week.  The numbers are generally below the economic thresholds. Nevertheless, scout your fields as numbers and conditions for populations to explode vary greatly.  For example, the grasshopper count in the winter wheat and winter rye variety trials at the Northwest Research & Outreach Center is close to reaching the threshold.  The bigger news, however, is that Cereal Leaf Beatle (CLB) has now been confirmed in three fields in northwest Minnesota. Drs Ian MacRae, Angie Peltier, and Anthony Hansen already alerted to the presence of this newcomer to Minnesota in a Minnesota Crop News article Thursday.

The scouts have only found a few instances of tan spot in wheat and net blotch was found on volunteer MN-Equinox at the NWROC.  The overall risk for leaf diseases, including leaf rust, will likely continue to be low with the lack of rain and relatively low dew points not allowing for long enough dew periods to form. Likewise, I do not expect the risk of FHB to be high in the later winter wheat or the earliest spring wheat that is reaching anthesis in the next few days.

The only really noteworthy disease observation is the occurrence of Wheat Streak Mosaic Virus (WSMV) in a field of spring wheat at the NWROC. WSMV is a rare occurrence in northwest Minnesota. Although I expect a substantial yield loss in the area of the field that is affected, it is a cautionary tale about the green bridge more than anything else.  In this instance, a few things came together that allowed this infection to occur. First, the winter wheat was seeded last spring in the alleys of the spring wheat and barley yield trials with the goal to suppress weed emergence later in the season.  This winter wheat was allowed to continue to grow for the remainder of the growing season. The very dry summer and fall, followed by the plentiful snow this winter, created ideal conditions for a wheat curl mite population to thrive and survive.  The winter wheat greened up nicely after the snow finally disappeared and was only terminated with a burndown application of glyphosate just before the soybeans were no-till seeded.  By that time the spring wheat in the adjacent production field had emerged. As the winter wheat wilted and dies back, the wheat curl mites population must have dispersed with a southerly wind, landing in the adjacent field. Had the wind been from an easterly direction it would have reached this year's small grain yield trials instead of the production field.

Spring wheat seedlings infected with Wheat Streak Mosaic Virus (WSMV). Note the stunted, yellow appearance and reduced tillering of infected seedlings.

Bottomline - a perfect, but easily avoidable, green bridge had been created that allowed this to happen. 

Several times this spring the thought had crossed my mind that the 'volunteer' winter wheat should be terminated sooner rather than later.  I was too busy with seeding the spring wheat trials that I never acted upon the thought. Lesson learned.

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