Due to the dry weather, early season fungal diseases were low or not even present, i.e., no reports of stripe and leaf rust. I did not recommend a fungicide application prior to flowering this season, save the application and product cost. However, dependent on the near-term precipitation and irrigation applications, wheat field may still benefit from a foliar fungicide after heading at the start of flowering. Fusarium head blight (FHB), also called head scab, is a fungal disease that infects wheat during flowering, which typically occurs between the third week and fourth week of May in this area. Over the past 15 years widespread FHB epidemics occurred in Nebraska in 2007, 2008, 2015, and 2019. Southeast Nebraska is particularly prone to FHB issues. In addition to yield loss as high as 50%, FHB reduces grain quality and the received price at the elevator due to damaged kernels or presence of a mycotoxin.
The pathogens causing FHB are always present in the area as it survives on corn and wheat residue. In May, excessive and frequent rainfall two weeks prior to flowering and during flowering creates a potential high FHB risk. Other factors will increase risk of FHB including planting a susceptible variety, planting after corn or wheat, no-till, and recent irrigation. What can we do to protect the wheat from FHB?
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Fungicides can significantly suppress FHB by 70%, but not completely control it. There are six fungicides recommended and labelled to suppress FHB including Caramba, Sphaerex, Miravis Ace, Proline, Prosaro, and Prosaro Pro. Large ground sprayers (>90 ft boom width) are very effective due to high volume application capability (>10 gpa), reduced tire damage to spray area ratio, and by using recommended nozzles (front & back angled nozzles). Aerial application is often chosen since ground sprayers are tied up with corn and soybean herbicide spraying or because wet weather limits field traffic. The effectiveness of aerial applications to suppress FHB can be improved if the volume is increased to 4 to 5 gallons per acre.
Target fungicide application during early flowering (Feekes 10.5.1) when yellow anthers first become visible. Miravis Ace and Prosaro Pro are labeled for suppression of FBH prior to flowering during heading, but it is still less effective than use during early flowering. From early flowering, applications can still be made 7 days later with very good suppression of FHB. Applications at the end of flowering lose effectiveness and can become off-label applications due to a 30 to 32-day preharvest interval or a growth stage restriction at the watery-ripe stage (Feekes 10.5.4). It is preferred that it does not rain 2 to 4 hours following the fungicide application.
Additionally, the six fungicides mentioned are labeled to provide 2 to 3 weeks of residual activity during the early grain fill period for stripe and leaf rust. However, there are no reports of leaf or stripe rust in the region, which is good. For more information about these and other agronomic issues, contact me at nathan.mueller@unl.edu or 402-821-1722. Know your crop, know your tech, know your bottom line at croptechcafe.org.
