Fusarium head blight or scab was first reported in 1898 or 122 years ago in Nebraska. Though not a severe disease each year, it was a problem in 2019. Will it be a problem in 2020 for wheat growers in southeast Nebraska? Plan ahead, pun intended. It is one disease that wheat growers should have a management plan. The financial implications of scab were estimated at over 3 billion dollars in farm-gate losses during the 1990s alone in the United States.
This disease infects the head at flowering through soft dough and is driven by the three factors of the disease triangle: A susceptible host, presence of the pathogen, and a conducive environment. When it comes to scab, we already have two (susceptible variety and pathogen) of these three factors present each year. The causal fungal pathogen (Fusarium graminearum and boothii) is present since corn and other weed species are alternative hosts. Second, many of the wheat varieties in the market place adapted to our area are rated as moderately susceptible to this disease. Even the best rated wheat varieties adapted to our area (e.g. WB4699, Zenda, SY Benefit, Overland) are considered moderately resistant (rated a 3 or 4 on a 10 point scale, with 1 being resistant) to scab. What is a conducive environment for scab? Frequent rainfall events the two weeks prior and during flowering will favor the development of scab.
There are numerous questions to answer when planning for a fungicide application to help suppress scab. Does the weather outlook look wet? Did I plant a variety that is more susceptible to scab? Do I know what fungicides work best to suppress scab? If hiring an aerial or custom applicator, do I have field maps ready and have I checked on product availability? If I am using my own ground rig or applicator, do I have the correct nozzles? Do I know how to determine the growth stage of the wheat and the best time to spray for the highest suppression of scab? Where can I learn more and whom can I call if I have questions?
Here are my quick answers to those questions. Visit the website that predicts the risk of scab given the weather forecast and variety susceptibility at wheatscab.psu.edu. View the 2019 UNL Fusarium head blight variety resistance ratings at cropwatch.unl.edu/2019/fall-wheat-disease-management-strategies-reduce-losses-2020 or contact me at 402-821-1722 or nathan.mueller@unl.edu. Fungicides for scab suppression include Caramba, Proline, Prosaro, and Miravis Ace. If the fungicide you have or want to use is not one of these four listed, again contact me, it does matter! Get field maps ready and check on availability and price of those four fungicides. There are specific nozzles for spraying scab with your own ground rig, nozzles that apply forward and backwards at specific angles provide the best coverage and scab suppression. Can’t order new nozzles in time, then adjust all nozzles at a 30-degree angle from horizontal. The best time to spray is at the Feekes 10.5.1, or 15% flowering and then within the next 5 to 7 days following that growth stage. View the University of Wisconsin, visual guide for winter wheat growth staging at my website croptechcafe.org/winterwheat. You can learn more about scab on our UNL website at cropwatch.unl.edu/plantdisease/wheat and of course, you can contact me or your industry agronomist with questions. Know your crop, know you, know your bottom line.
