Over the last 10 years or so, there has been an increase in Fusarium Head Blight (FHB or head scab) in wheat planted in North Carolina, South Carolina and Virginia. The reasons may vary, but the chance of FHB in wheat increases if you plant wheat behind corn. But like any disease, it takes a host, a pathogen and favorable conditions for disease to develop. High humidity, rainfall at or near heading and warm temperatures are key factors. The most favorable conditions for infection are prolonged periods (48 to 72 hours) of high humidity and warm temperatures (75 to 85o F). However, infection does occur at cooler temperatures when high humidity persists for longer than 72 hours.
FHB is caused by the fungus Fusarium graminearum or Gibberella zeae, both commonly found in corn or wheat residue. In corn, the disease is called Fusarium Ear Blight. The fungus attacks the grain resulting in yield losses. In wheat, FHB symptoms are confined to the head, grain, and sometimes the peduncle (neck). Typically, the first noticeable symptom is bleaching (then turning pink or orange) and can include tan or brown lesions on some or all of the spikelets. FHB-diseased heads are easily spotted if there are healthy green heads nearby. Wheat is susceptible to FHB infection starting at flowering (Feekes 10.5.1) and continuing through early dough stage (Feekes 11.2).
While yield loss is the number one concern, other losses come in the form of wheat being docked or turned away from buying stations due to high levels of vomitoxins that are produced by the fungus in diseased grain. Vomitoxins, scientific name deoxynivalenol (DON), are mycotoxins which can be toxic to humans and animals at high levels. Vomitoxins are found in many grains such as wheat, barley, oats, rye, tritacale and corn. The US FDA has set maximum DON levels that are allowed for human consumption and livestock feed. (Thresholds are documented on the FDA website).
To effectively manage FHB requires a whole farm approach. Management strategy should include selecting wheat varieties with some resistance or tolerance to FHB, managing crop residues, planting high-quality seed, and using fungicides. No single disease management tactic will provide adequate control or suppression of FHB, especially if environmental conditions are favorable for disease development.
Managing corn residue will reduce the amount of overwintering inoculum. Planting wheat into corn stubble greatly increases the likelihood of FHB development, so wheat should follow non-host crops like soybeans, peanuts, cotton, tobacco or sorghum.
Fungicides are our only tool once we reach conditions that are favorable for FHB development. The fungicide’s ability to effectively suppress FHB depends on application timing, spray coverage, and disease pressure. Sprayer recommendations for suppression of FHB include angling all spray nozzles forward 30-45 degrees down from horizontal. 30 degrees is preferred over 45 degrees. You will need enough pressure to produce fine to medium size spray droplets ranging from 250-300 microns (if you are using a flat fan nozzle). Position the nozzle 8-10 inches above the grain heads. Volume is important, so apply the fungicide in a minimum of 10 gallons per acre. The addition of a spray adjuvant such as Matrixx will improve fungicide coverage, spreading and deposition into the head.
Triazole fungicides are the only products labeled for use against FHB in wheat. Only 3 active ingredients are labeled – prothioconazole, tebuconazole and metconazole. Prosaro® is a premixture of prothioconazole + tebuconazole, Proline® is prothioconazole and Caramba™ is metconazole. Application of these are most effective if applied at early flowering or Feekes 10.5.1. Absolutely do not use any fungicide that contains a strobilurin mode of action to manage FHB. Strobilurin fungicides have been known to increase the severity of FHB.
Contact your Coastal AgroBusiness representative for the proper fungicide rate, timing and adjuvant recommendations.
Always read and follow label instructions.
Information provided by Coastal AgroBusiness, Inc.
Caramba is a trademark of BASF Corporation.
Proline and Prosaro are registered trademarks of BAYER CropScience.
Matrixx is a product of Coastal AgroBusiness, Inc.