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Scab Epidemic Risk Model

July 27, 2020

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Plant Pathologist Commentary: This will likely be the last small grains disease update for the 2020 cropping season. I didn’t update the commentary at the beginning of the week as nearly all wheat and barley acres reached anthesis the week before and all fungicide decisions for the season had been made. Instead, I took the past few days to get some idea of how widespread and severe FHB infections are in the region. It is not hard to find FHB in the yield trials in NW Minnesota. The field severities are nowhere near disastrous but high enough in some of the more susceptible varieties that you would be faced with discounts upon delivery of the grain to the elevator because the DON content will exceed the 2 ppm limit. Severities in the few commercial fields I scouted and some of the comments I received from crop consultants to date is that FHB severities are not bad and even a bit lower than last season. The major difference between the trials and the commercial production is variety selection and the application of a fungicide at Feekes 10.5.

Nonetheless, I encourage to evaluate the extent of the FHB infections in the next two weeks. This is an important first step to not just become aware of the extent of the damages but also to start developing a plan of attack to minimize the impact of these FHB infections on the grain quality.

Your first step to maintaining quality and avoid the potential discounts due to low test weight, fusarium damaged kernels and the presence of DON is to segregate the worst affected fields or areas of fields and not co-mingle the grain. Your second step is to increase the fan speed during harvest to reduce the number of fusarium damaged kernels in the grain tank.

Unfortunately, you will also increase your harvest losses as you increase your fan speed as smaller but otherwise sound kernels will also be left in the field. Often these smaller kernels come from the spikelets above the initial point of infection and where the FHB has grown into the rachis, thereby halting the grain fill of the kernels higher on the rachis. I expect kernel weights to be down anyway as the heat and humidity we have had to endure to date will likely result in smaller kernels than most years.

If needed, the next step is to use a grain cleaner to further reduce the number of fusarium damaged kernels. A Kwik-Kleen grain cleaner or equivalent allows you to clean the grain prior to putting the grain in storage.

Meanwhile, the Wheat Stem Sawfly is completing the summer portion of its life cycle as the larvae are reaching the bottom of the infected stems and are now starting to girdle the lower portion of the stem to build the hatch in their home for the winter in the small piece of stem just above the crown but below the soil surface. Stems infected with WSS will start falling over anytime after the crop has reached physiological maturity and is drying down.

The WSS were alive and well in the Crookston and Fisher area earlier this season when we monitored their emergence. However, I also have received reports of WSS from as far south as Glyndon and well east of Crookston. These are just a two reports but if confirmed it points to a further spreading of this ‘ink stain’. I once again ask for your cooperation and report any fields you suspect WSS infections.

Good luck and stay safe with the harvest!

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