Fusarium Head Blight or Head Scab of Wheat

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Wheat in most of Delaware is approaching heading or heads have emerged and could be flowering by the weekend depending on temperature. The risk of head scab or Fusarium head blight has increased with the recent wet weather pattern, which might continue into next week. Growers need to carefully evaluate the need for fungicides that could help suppress development of the disease. In the past we have not had good fungicide options but now that we have several fungicides with the capability to suppress the disease this option should be considered if the risk is high enough and it is economically sound. If the current conditions persist, large areas of Delaware could be at risk for scab infection. The new risk management tool is located at the Fusarium head blight website http://www.wheatscab.psu.edu. It can be useful once heading begins and the risk of scab increases as flowering approaches. The new version that is running now has the ability to give a 24-72 hour forecast looking at the previous several days as well as the weather forecast for the next several days. Those buttons are at the top left side of the forecast page.

Fungicide applications at heading but before flowering have not been very effective and are not recommended for scab suppression. The final decision to spray must be made as close to flowering as possible.

Fungicides must be applied at the correct time to control Fusarium head blight. 

First choice of products for scab suppression is Prosaro at 6.5 fl oz/A or Proline at 3 oz/A tank mixed with Folicur at 3 oz/A, second choice is Proline at 5.7 oz/A or Caramba at 14 oz/A, third choice is Folicur at 4 oz/A. Note Folicur is the weakest product for scab suppression and at best will only produce a slight reduction in disease. Folicur should only be selected if none of the other recommended products is available. No other products are registered for application at flowering and strobilurin-containing fungicides that are not registered for scab suppression may even increase vomitoxin in the finished grain. Use only recommended products when the risk warrants their use and apply as close to initial flowering as possible to be effective against scab.

Below are some suggestions that can help to evaluate the risk of disease:

Previous Crop: The fungus that causes head scab survives in the residues of many grass crops. The fungus is also a pathogen of corn and the most severe disease often occurs when wheat is planted in fields with large amounts of corn residue left on the soil surface. Planting wheat into wheat residues also increases the risk of scab, but this residue tends to break down more quickly diminishing the risk of disease relative to corn residue.

Resistant Varieties: All but a few wheat varieties that we grow are susceptible to head scab and the few that have some resistance do not provide enough resistance to protect the crop from a severe outbreak of the disease.

Weather Conditions: The infection of the wheat takes place at flowering or during the early stages of the grain filling period. This time period clearly influences the amount of disease present. However, the weeks preceding flowering are also important. Frequent rainfall and extended periods of high relative humidity prior to flowering favors the reproduction of the fungus that causes head scab. In fact, some of the worst epidemics of scab occur when conditions are favorable for reproduction of the fungus prior to flowering followed by a few days that are conducive for infection during the flowering or early stages of grain fill.

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