To Manage Your Wheat Crop Infected With Head Scab
On June 25, 2018
With the extremely wet weather we have experienced this year, the wheat crop is heavily infected with disease. Head scab of wheat (a.k.a. Fusarium head blight) is caused by the fungus Fusarium graminearum, which can also infect corn and other small grains. The fungus survives on the residue of these crops and starts becoming active and making spores that can infect new crops when the weather becomes warm and wet. If this happens when wheat is flowering, the fungus can enter through those flowers and cause your grain to become infected. In a year of high disease pressure, when you know you’ve got scab in the field, what are your options? The answer will differ from grower to grower, but here Extension Plant Pathologists Alyssa Collins and Paul Esker discuss what you should be considering and actions you can take.
One of the side effects of this infection is the production of toxins (deoxynivalenol, DON, or vomitoxin, most frequently) which can render your grain unsellable or cause it to be discounted. For more information on how to evaluate your fields for this disease see this article: https://extension.psu.edu/assess-your-wheat-for-scab
Even those farmers that applied a timely spray to at-risk small grains will see some symptom development in a high-pressure year. This is because even the best products applied at the perfect time (at the onset of flowering) do not give 100% protection. At best, these fungicides can offer a 50-60% reduction in disease severity and, ultimately, DON production. If a spray was applied before flowering, disease control will be even less. The uneven flowering timing of the crop makes targeting an application to protect every flower in the field impossible with a single fungicide pass.
If you have high scab levels in your fields, chances are very good that your neighbors and most of the farms in the region are also facing the same thing. This creates an economic situation that is going to be challenging for the region. Chances are good that all elevators and mills will be testing for DON and implementing thresholds for acceptance and docking. High scab incidence does not automatically mean high DON levels, but it does mean there is a potential for high DON. Despite this, some mills may consider not accepting feed grain from the region during this time or may offer an extremely low price for any wheat they accept. If you don’t have a contract, call the elevator or mill you intend to deliver to ahead of time to see what the situation is. If you do have a contract, you may be able to work with your buyer to convert your contract from, say, flour-grade to feed grade bushels.
If your wheat acres are insured, contact your insurance agent prior to harvest. They may send an adjuster to be present to sample your harvested grain and ensure it is sent to an approved lab for toxin testing. Depending on your policy, you may have a claim in a high-scab year.
For harvest, there are some measures you can take to help drive down toxin levels. First, identify fields that have the least amount of scab and consider harvesting and delivering these separately from severely infected fields. Fields often have levels of infection that vary on the edges or from field to field based on planting date, flowering date, and variety. You may also want to segregate these areas as well. This can help prevent contamination of your cleaner grain which may be of higher value.
If you find you have more than 25% of your heads affected by scab, consider harvesting it using a high fan speed on your combine which helps to clean out the lighter, infected kernels (which are highest in DON). Recent research (Salgado et al., 2011) showed that adjusting the combine’s fan speed to 1,375 or 1,475 rpm, with a shutter opening of 90 mm (3.5 inches) had lower Fusarium damaged kernels and DON levels. Discounts were also lowest with these settings, as well as lower at the higher fan speed with a shutter opening of 70 mm (2.8 inches). Seed cleaning is also a good option for removing the scabbier particles in a safe way for the grain.
Harvesting early (anywhere below 20% moisture) can often result in better quality grain and less toxin in the long run. The downside is the cost of drying, but the advantages typically outweigh that cost in terms of test weight, falling number, and DON. You also then have the opportunity to plant double crop beans earlier and make a better yield. Drying does not reduce the amount of DON in the grain, but it will kill the fungus and keep it from producing more.
If you planned to use or sell the straw from scabby fields, be aware that DON can also affect the straw. Avoid using these fields for straw intended for sensitive applications like horses or swine.
Here are some take home messages for the 2018 harvest. Scab infection risk was high during our entire flowering period across much of PA. The strategy of multiple planting dates or use of varieties that flower at different times is not one that would have been successful this year. Even if you did everything right, you may experience some scab in your crop this year. Harvest as soon as possible and dry down that grain below 15%. We are looking at deep discounts this year from buyers. Check with your insurance company before harvest. Think about your straw in scabby fields and avoid using for sensitive animals like horses. Call your intended recipient first, before showing up with a truckload of grain to find out this year’s procedures for testing and dockages. Don’t save any grain from scabby fields to plant this fall. The fungus will survive seed storage and potentially reduce germination and cause seedling diseases.
Collins and Esker offer these thoughts on planning for next year. First, always choose a moderately resistant variety. When combined with well-timed fungicides, this gives the best protection against vomitoxin that exists. Plant varieties that head out at different times. This can spread your risk so that, hopefully, if risk levels are high while some varieties are flowering, they will be low for other varieties. Next, manage your residue. Plant into well-sized residue so that your seed emerges uniformly. When wheat emerges uniformly, it tillers and heads uniformly, making it easier to apply fungicides in a timely manner. Don’t plant wide-row wheat. This also contributes to uneven tillering. Earlier is not better when spraying for scab, wait for flowering. You can still spray up to ¼ milk kernel and get some efficacy. Any later and you’ll run into post-harvest interval restrictions. Go to the scab risk prediction website and track risk levels during and after flowering www.wheatscab.psu.edu . Even if you are going to spray no matter what, this can give you an idea of how much scab you are likely to see. Then you can anticipate vomitoxin levels and measures you’ll need to take at harvest.
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