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Fusarium graminearum fungicide application control option

July 6, 2016 - Fusarium graminearum (Fg) is a serious fungal disease of cereal grains. Although yield is affected, the negative impact the disease has on grade results in poor quality grain intended for feed, malting, milling and the biofuel industry. Recent surveys indicate Fg is established in southern Alberta, and traces are present in central and northern regions of the province.

"Fg can be effectively controlled under normal conditions using a combination of disease prevention strategies throughout the growing season," says Neil Whatley, crop specialist, Alberta Ag-Info Centre, Stettler. "When weather conditions are favourable for infection, and in irrigated cropping systems, an in-crop fungicide application may be considered, but only provides disease suppression."

Cereal crops are most vulnerable to Fg infection at flowering time if weather conditions are moist and warm, and if the disease is established in the lower canopy. Disease spores are spread by rain splashes and wind to infect open flowers.

"Observable Fg symptoms don't appear until the late heading stage when it is too late to apply protective fungicide," says Whatley. "A decision to apply a fungicide must be made prior to this, at the early flowering stage. If disease risk level is assessed as moderate to high, and yield return justifies fungicide application cost, a foliar fungicide application should be applied at early flowering to protect open florets."

A fungicide application is recommended if the risk level for Fg is moderate to high. Disease risk level increases when more of the following factors exist:

• field is located in a region where Fg is established
• cereal variety being grown is susceptible to Fg
• durum or corn is in the crop rotation
• cereal crops are frequently grown in the same field or in nearby fields
• weather conditions are damp and warm at crop flowering stage
• irrigation is used in the farm operation
• yield potential is good
• cereal grain prices are high

"Application of a fungicide too early is better than too late," says Whatley. "With wheat, flowering begins three to four days after head emergence and lasts approximately seven days. The optimum stage for fungicide application is during early flowering when some visible anthers are present on the head."

With barley, flowering begins just prior to head emergence and continues during heading, lasting approximately 14 days. The optimum stage for fungicide application is when the spike is fully emerged from the boot.

"Studies indicate that Fg control is improved by directing spray nozzles at 30 degrees from the horizontal either forward or backward or simultaneously forward and backward, and using a high water volume to optimally cover grain heads," explains Whatley. "While 10 gallons (45 litres) per acre of water are adequate for spring wheat, 18 gallons (80 litres) per acre are recommended for durum as durum grain heads are more difficult to wet."

The most apparent Fg disease symptom is premature bleaching or blighting of one or more spikelets in the head, which stands out on green heads. "Under prolonged humid conditions, orange-coloured fungal spores appear on blighted parts of the head. If these symptoms are observed, send a plant tissue sample from the infected head area to a lab to determine whether it is the graminearum species of Fusarium. Recall that these observable Fusarium disease symptoms don't appear until the late heading stage when it is too late to apply protective fungicide, but are good indicators to inform whether Fg is present in the field or not. If humid conditions persist, the pathogen can cause higher mycotoxin levels by spreading to other kernels and heads after seed set."

July 7, 2015  By Alberta Agriculture and Forestry