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Head scab threat is low, but be ready

green wheat and barley
HEADS UP: Wheat and barley are starting to head in many southern areas of the Northeast, meaning that it’s time to start paying attention to weather conditions as the threat from fusarium head blight can change rapidly.
Once wheat starts heading, check the online risk tool to see whether a fungicide treatment is needed.

Barley and winter wheat are starting to head in many areas, especially Maryland and Delaware. That means that it’s time to stay ahead of potential yield robbers, including the biggest one of all — fusarium head blight, also known as head scab.

Only 6% of barley in Pennsylvania is heading right now, according to the first National Agricultural Statistics Service Crop Progress report for May. Delaware and Maryland fields are much further ahead, which is no surprise. Maryland’s Crop Progress Report showed 30% of barley heading, while 51% of barley and 38% of winter wheat fields are heading in Delaware.

A Penn State Extension alert from Wednesday stated that disease pressure is low right now with cooler temperatures, low humidity and high winds, but this can change fast with more rains and warmer temperatures.

When this happens, “We should expect to see increased levels of common foliar diseases like powdery mildew and leaf blotches, and a greater threat of fusarium head blight,” according to the alert.

Foliar fungicides to protect barley from scab should be applied at 50% heading or shortly thereafter, according to the alert. Once the crop starts heading, there is a five- to six-day window to apply a fungicide. Current labels state that the last stage of application is midflowering, and then there is a 30-day harvest restriction.

“Do not use any of the strobilurins [Quadris or Headline] or strobilurin/triazole [Twinline, Quilt or Stratego] combination products at flowering or later. There is evidence that they may cause an increase in mycotoxin production,” the alert states. “Caramba, Miravis Ace and Prosaro all provide very good scab suppression. The Miravis Ace label allows for earlier application than Caramba or Prosaro, but best results are still achieved when application is timed at heading in barley. Spray nozzles should be angled at 30 degrees down from horizontal, toward the grain heads, using forward- and backward-mounted nozzles or nozzles with a two directional spray, such as Twinjet nozzles.

“Additionally, a fungicide treatment at heading using any of these products will also give you excellent control of most leaf diseases as well,” the alert states.

The Crop Protection Network, run by Cooperative Extensions around the country, has released its “Fungicide Efficacy for Control of Wheat Diseases” guide. The guide is handy because it lists several fungicides and their efficacy against the most common barley and wheat diseases.

“Not many changes to last year’s version. Preemptor SC was removed. It’s an older chemistry, less widely marketed now and not labeled in some states,” says Alyssa Collins, plant pathologist with Penn State Extension. “Quadris [azoxystrobin] was added as it has been shown to have excellent or very good efficacy for several of the foliar diseases.”

Watching for head scab

Very few fungicide products are effective against fusarium head blight, and even they don’t provide great control.

So if you didn’t plant an FHB-resistant variety last fall, timing will be important to stay ahead of this devastating yield robber. The good news is that as of right now, the risk is low for head scab development, according to the Fusarium Risk Tool.


Flowering, which happens three to five days after wheat starts heading, is prime time for the fusarium fungus to develop. You also need high humidity — at least 85% humidity — and temperatures between 68 and 75 degrees F.

In a previous article, Collins talked about the effects of DON levels in wheat, whether it’s being transported to an elevator or fed to livestock.

Regional head scab conditions, as well as the quantities of clean grain available, will affect thresholds for DON rejection or dockage the most.

If you notice head scab and you intend to feed the wheat to animals, the crop should be tested. FDA advisory levels are 10 parts per million for ruminating beef and feedlot cattle older than 4 months (cannot exceed 50% of diet); 10 ppm for poultry (cannot exceed 50% of diet); 5 ppm for swine (cannot exceed 20% of diet); and 5 ppm for all other animals (cannot exceed 40% of diet). 

The level is 1 ppm for immature and lactating animals.

TAGS: Wheat
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