Conditions favorable for wheat scab again this year

Fusarium head blight, also known as FHB or scab, devastated Louisiana’s wheat crop last year and while many hoped the worst was over, recent reports are predicting it could happen all over again this year.

Scab is mainly caused by the fungus, Fusarium graminearum, which can develop rapidly during wheat’s flowering stage when accompanied by warm and wet weather, similar to the conditions Louisiana is currently experiencing statewide.

Symptoms of scab typically first appear 10–14 days after flowering and are already present in the southernmost production regions of Louisiana. At this point, bleached heads are noticeable, which can sometimes be mistaken for the appearance of maturing wheat. Upon closer inspection, however, the affected wheat heads will usually have infected kernels showing the characteristic bleached appearance with pink/salmon/light orange coloration along the glumes.

A recent article explains that this coloration indicates millions of microscopic spores (reproductive structures) of the fungal pathogen. There are usually healthy kernels among the diseased kernels, but in extreme cases the entire head may be infected. At harvest, affected seed will be shriveled, off-color, and much lighter than healthy kernels.

Farmers in Louisiana, however, are not the only ones who need to worry, as recent reports from North Carolina show weather conditions favorable for scab as well.

“There was a terrible scab epidemic last year, particularly in Louisiana, and all the way over to Georgia. People have never seen such bad scab,” Christina Cowger, a small gains pathologist at North Carolina State University, said in an article. “It devastated the wheat industry in that area, so this is a real problem. It could have just as easily been North Carolina that was devastated by scab. It’s all about the weather,” she continued.

In addition to the weather, wheat variety is another major factor when it comes to assessing scab risk, Cowger explains.

While none of the commercial wheat varieties are fully resistant to scab, a survey conducted in North Carolina showed that just 15% of the soft red winter wheat varieties planted in the state were moderately resistant to scab. Also, 50% of the acres reported were susceptible or moderately susceptible to scab.

In another survey, 200 respondents from 15 counties said they planted wheat — representing a total of 82,000 acres planted. That survey revealed that only 22% of those 82,000 acres were moderately resistant to scab. The rest of the acreage was either susceptible or moderately susceptible.

Based on this data, Cowger said above all else she encourages farmers to consider planting varieties that are moderately resistant to scab and that wheat growers should always carefully monitor and manage the disease when it appears.

“On average, good scab-resistant varieties are going to be as profitable we predict as scab susceptible varieties when you factor in the scab risk, scab pressure and dockage policies,” Cowger added.

Other cultural practices that may aid in management of scab include crop rotation, tillage, mowing/shredding, or staggered planting/varietal maturity. In addition, at harvest, combine fan speed may be increased to remove infected seed, which is lighter than healthy seed. Seed cleaning equipment may also help remove affected seed but may not be cost effective. Along with these cultural practices, research shows the appropriate application and timing of fungicides is also critical.

The article goes on to explain that growers have a very short window during flowering to make an effective application for scab. The biggest problem is that ideal conditions (wet weather) for scab infection are not ideal for making fungicide applications.

Even so, Cowger explains that national fungicide trials conducted over many years show that the best fungicides offer 38 – 45% control of the disease. “They only reduce the disease partially, and those are the best products,” she added.

“You’re still going to have a lot of scab even if you spray under the best timing and manner possible if you plant a susceptible variety,” Cowger said. “You have to use both approaches to protect yourself fully in a bad scab year. That’s why we say plant moderately resistant varieties plus use a fungicide when the risk is high. That’s what we call integrated management. It’s really the only way to tackle this scab problem effectively.”

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