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Small Grains Disease and Pest Update 06/22/22

This weekend's record-breaking heat stalled the risk of initial infections of most all of the foliar fungal pathogens and Fusarium Head Blight.  As temperatures have dropped from their record highs and a couple of cold fronts have resulted in widespread thunderstorms across the northern half of Minnesota, the risk of initial infections of tan spot and leaf rust is increasing again. A quick check of your pant legs at 10:00 in the morning or 9:00 at night will be very telling - if you end up with wet pant legs you probably are encountering long enough leaf wetness periods for either disease to start. If you find tan spot while scouting for weeds and testing how waterproof your workboots really are, 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 still have not received any reports of stripe and leaf rust in wheat or crown rust in oats.  Most of the oats in Souther Minnesota are now between the flag leaf stage and heading. Check your fields for any sign of crown rust in the lower and middle canopy, especially near treelines, river banks, farm yards, or any other place you might find buckthorn.  The immediate forecast will be relatively favorable for crown rust just to start, especially in more wooded areas of the state where dews take longer to burn off. Spray a full rate of a labeled fungicide in oats that has a very good or excellent efficacy rating for leaf or stripe rust in wheat and follow label restrictions for oats.

Meanwhile, the first barley fields in southern Minnesota are heading.  The risk of Fusarium head blight dwindled with the high temperatures and the lack of widespread rain events across the southern half of teh state.  The risk is predicted to wain with the extreme heat that is forecasted.  

The optimum timing to suppress scab in barley (and control any leaf diseases that also may be present) remains at Feekes 10.5 (or fully headed). Miravis Ace provides a wider application window as it maintains adequate suppression up to 5 days after Feeks 10.5 compared to the other fungicides labeled for suppression of FHB. Overall, I expect the risk of FHB to start increasing again by this weekend, especially in those fields that did receive some precipitation about a week to 10 days ago or that are under irrigation and received water during that same timeframe.  If you grow Pinnacle, I suggest you spray a labeled fungicide regardless as this variety is too susceptible to net blotch to leave unprotected.

Finally, there have been several flights of armyworms into the state, and moths have been caught in suction and pheromone traps from south-central Minnesota all the way up to Roseau and Lake of the Woods counties on the Canadian border.  The first armyworm moths were caught over the Memorial Day weekend with additional flights in the following two weekends (I guess they also are 'Going up North to the Lake' during the weekend). Their brood takes some 8 to 10 days to hatch.  While the first few instars do not do a lot of feeding damage, the last two instars can do a lot of damage.  Scout for armyworm on headlands and lodged grain first. Frass pellets confirm that there are armyworms present as larvae are shy of full sunlight and will hide near crowns and under clumps of soil. The threshold for treating armyworms is 4-5 larvae per square foot.

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