Fusarium Head Blight Timing and Tank-Mix Decision in Wheat
A 60-acre field of winter wheat in eastern Arkansas is at Feekes 10.5.1 (beginning flowering) on April 22. The field was no-tilled into corn residue, and the variety is moderately susceptible to Fusarium head blight (FHB). The forecast shows 0.8 in. rain tonight, 70-75 F, and 85% relative humidity for the next four days. The grower has a ground sprayer with drop nozzles and a product containing metconazole on hand; the label lists a 35-day preharvest interval. Estimated harvest is June 5, 44 days away. The grower also has a strobilurin product and asks whether he can tank-mix it to improve disease control and save a pass.
1. Should the grower spray for FHB, and if so, what timing and application method?
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The risk is high: corn residue is the inoculum source, the variety is moderately susceptible, and the forecast is warm, humid, and rainy for four days. The protection window for FHB is early flowering, Feekes 10.5.1, and up to about 4-6 days later. Spray now. Metconazole is a triazole with activity against Fusarium and can reduce DON, so it is a reasonable choice. Use a ground sprayer with forward- and backward-angled nozzles or drop nozzles to reach the wheat heads; a flat-fan boom alone leaves the heads underprotected. Use 15-20 gal/ac and moderate pressure. Do not wait for the rain to pass if the field is trafficable; the infection period is during flowering. If the field is too wet to enter, an aerial application is better than missing the window.
2. The grower wants to add a strobilurin to the tank to broaden disease control. Evaluate that decision.
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Do not tank-mix a strobilurin for FHB. Strobilurins are weak against Fusarium and some labels warn that they can increase DON when applied at flowering. They also select for resistant populations and add cost without improving FHB control. The triazole should be the base. If leaf rust or powdery mildew is also present, choose a labeled triazole or a pre-mix with proven FHB activity, but not a straight strobilurin at this timing. Keep the sprayer clean and follow the label; mixing order and adjuvants matter. The goal is to protect the heads during the infection window, not to cover every disease with one pass.
3. Check the preharvest interval and decide whether the metconazole application is legal. What if harvest is moved to May 28?
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April 22 plus the 35-day preharvest interval is May 27, so an application on April 22 is legal if harvest occurs June 5, 44 days later. If harvest is moved to May 28, that is only 36 days after April 22, still one day beyond the 35-day PHI, so it is legal but tight. If harvest moves to May 25, 33 days, the application would be illegal. The grower should record the application date and check the label, because PHIs differ among products. If the only effective product has a PHI that conflicts with the expected harvest, choose another labeled triazole with a shorter PHI or accept a lower level of control. Do not apply after the legal cutoff, and do not rely on a later harvest date that weather may change.