Fungicide spraying wheat for scab must be very timely

After the horrible wheat scab year in Missouri in 2015, the state’s farmers and their crop advisors are watching maturing wheat with worry this spring. But no matter how antsy a farmer might become, ag professionals must reinforce a University of Missouri agronomist’s warning about spraying at the right time.

Spraying must be timely to be most effective. “Don’t rush out to put on scab fungicide until flowering begins,” said Greg Luce, MU Extension small-grain specialist. “Ideal timing is at start of flowering. Being a little late is better than being too early.”

Last year, fusarium head blight, often called scab, cut yields and reduced seed quality in Missouri. Many elevators turned away truckloads of scabby grain. Besides yield loss, a big problem was that the infected wheat carried vomitoxin, which can make grain unfit for livestock feed.

“With rain week after week, last year was perfect for scab to occur,” Luce said.

This year was dry as wheat developed. However, rains returned the last week of April as some heads emerged. Farmers could have issues again this season, Luce said. And warm, humid weather encourages spread of scab.

A further reminder from Luce is that fungicides can be used for control, but they should not be expected to provide complete control. It’s important to use recommended products, reading the label and applying the product timely and correctly.

Luce is cautioning about spraying too early. Spraying before flowering won’t be as effective, and timely scouting is required.

“Flowers on a wheat head don’t all appear at once.” Luce said. “Flowering starts in the middle of the head, then moves to the lower and upper segments. Wait for emerging anthers to be visible.” At bloom, flowerets extend a thin green spike called an anther.

There is a tight window for effective spraying, so preparation to spray or having custom application lined up is necessary for when first flowers appear. Analyzing local scab conditions by ag professionals can be helpful to farmers.

Luce explained that research at the University of Illinois showed that approved scab fungicides worked best at beginning of flowering. The data showed that spraying five days after the ideal timing was better than spraying when no anthers were present.

Luce and MU specialists across the state have reported uneven wheat growth in farm fields this spring, which is being attributed to a combination of cold waves and lack of rain. But it is too late to apply fertilizer to speed growth on spindly spots.

Something to consider for the future is that planting wheat after corn is worse than following soybeans. Corn can have stalk rot, caused by the same fusarium causing head scab in wheat. Farmers have to choose a variety with proven scab tolerance and be sure to plant clean, quality seed not contaminated by scab spores.


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