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Small Grains Disease and Pest Update 06/15/2022

The risk model for tan spot indicates that about half the days this past week have been favorable for initial infections, meaning that the canopy stayed wet long enough and at the right range of temperatures to allow spores to germinate and infect the wheat plants.  The risk has been higher further south and east.  The forecasted heat will likely halt additional infections and slow down the existing infections. Nevertheless, I encourage you to scout the spring wheat before you do your weed control and determine whether you have tan spot present in your field. If you find tan spot it is a good idea to add half a labeled rate of a fungicide to your weed control program. If you can not find any tan spot, do not add a fungicide and you save yourself some money.  Research from NDSU has shown again and again that you will not see a return on your fungicide application if no disease present at the time of the herbicide application. I have not received any reports of stripe and leaf rust in wheat or crown rust in oats as of today.  The risk models have indicated low risk and that risk is not expected to increase in the next couple of days. 

Meanwhile, winter rye is at anthesis across much of the state, and winter wheat in the southern part of the state is now at anthesis heading.  The risk of Fusarium head blight remains highest in the southeastern corner of the state.  East of  US Hwy 169 from the Iowa border to the Twin Cities is now at moderate risk while the area east of US Hwy 63 is now at moderately high to high risk. The risk is predicted to wain with the extreme heat that is forecasted.  

The optimum timing to suppress scab (and control any leaf diseases that also may be present) remains at Feekes 10.51 for winter wheat and rye for all fungicides labeled for use in the respective crops.  Miravis Ace provides a wider window of application as it maintains adequate suppression up to 5 days after the beginning of anthesis compared to the other fungicides labeled for suppression of FHB. The decision to use a fungicide in either winter wheat or winter rye has, given the immediate forecast, not become any easier as this extreme heat not only reduces the risk of infections it also creates a lot of stress on the crop, thereby reducing its yield potential.

I received a few reports of aphids in oats in southern Minnesota but none of those fields were at the economic threshold of 80% of the stems having at least one aphid on them prior anytime prior to anthesis.  Meanwhile, grasshoppers have emerged in numbers and it is not difficult to find the little nymphs on field edges.  Counting these little rascals in front of you to determine whether you are at the economic threshold of  50 to 75 nymphs per square yard is something different altogether. Using a 15-inch sweep net and making four 180-degree sweeps very close through the ground and more or less through the crop gives you a much better estimate of the number of nymphs per square yard.

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