Assessing Fusarium Risk Now Will Assist With Control Next Year

 
  From the July 31, 2017 Issue of Agri-News
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 Although when Fusarium graminearum symptoms are present in a field it may be too late to apply a fungicide, producers can still use the information they gather about the outbreak to plan for subsequent growing seasons.

“Fusarium head blight (FHB) is a fungal disease of cereal crops that affects kernel development,” says Neil Whatley, crop specialist, Alberta Ag-Info Centre. “FHB is well established in southern Alberta and trace amounts are found in central and northern regions.”

While caused by one or more species, Fusarium graminearum is considered the most important FHB species due to its aggressiveness and production of a toxin called deoxynivalenol or DON, aka vomitoxin. DON affects livestock feed, the baking and milling quality of wheat and the malting and brewing qualities of malt barley. Cereal grain, especially wheat, is graded based on the level of fusarium damaged kernels (FDK) in the harvested grain. Canadian Grain Commission grading standards allow very little tolerance of FDK in the top grades.

To help limit the impact of Fusarium graminearum, farmers should use a combination of disease prevention strategies throughout the growing season, says Whatley.

“The first step to trying to limit FHB is knowing whether the disease is present in a field by searching for and observing disease symptoms. Additionally, learning whether Fusarium graminearum is the dominant FHB species under observation, and becoming aware of its prevalence and severity, contributes to this first step toward potentially reducing its impact.”

FHB symptoms become visible in a developing cereal crop during the heading stage, typically once the plant reaches late milk to early dough during the last part of July or early August. The most apparent FHB disease symptom in wheat is premature bleaching of one or more infected spikelets in the cereal plant’s head, which visibly stands out on green heads. Rain-splashed spore growth appears as an orange, pink or salmon coloured fungal growth at the base and edges of the glumes on these blighted head parts. Symptoms in barley are much less distinct and the brownish dicolouration due to FHB can be easily confused with hail damage or symptoms of net blotch or spot blotch infection.

(Picture of premature bleaching of infected spikelet in wheat, courtesy of Kelly Turkington, AAFC.)

Diseased spikelets can contain visibly affected kernels. In grading terms, visibly affected wheat seeds are called fusarium damaged kernels (FDK), whereas in barley, it is called fusarium mould. FDKs in wheat are shrunken and are typically a chalky white colour, while fusarium mould on barley appears as an orange or black encrustation of the seed surface. Symptoms in barley may be confused with hail damage, kernel smudge, or infection by leaf diseases such as net blotch or spot blotch.

“Infection timing determines the severity of kernel damage,” says Whatley. “While infection occurring at early flowering can lead to complete abortion of kernels, FDKs generally result from infection from the early to mid-flowering stages. Late infections well after flowering and up to the soft dough stage of kernel development may not show visible symptoms; however, kernels can contain the fungus and, more importantly, the mycotoxin it produces."

If any symptoms are observed, Whatley says to send the affected cereal head samples to a lab to determine whether the Fusarium species is indeed Fusarium graminearum and to determine the disease prevalence.

“Routine testing of harvested grain and seed intended for planting is another way of assessing the presence and extent of Fusarium graminearum, especially if harvested grain is downgraded due to the presence of FDK. Several private seed company labs offer testing services for Fusarium graminearum in cereal seed/grain.

“Realizing whether a specific field is a candidate to apply a Fusarium graminearum control strategy is contingent upon the knowledge that was gained by observing disease symptoms at the heading stage of cereal crops during previous growing seasons as well as testing of seed and grain. Determining the FHB species and disease severity are the first steps to determining whether a control strategy is necessary. If Fusarium graminearum is not found in plant, grain or seed samples, a producer may want to be cautious about their seed source and ensure that they limit their exposure to this pathogen via infected seed. This is less of a concern where the pathogen is well established on crop residues from previous growing seasons. Ultimately, determining the need for a fungicide application in an area where Fusarium graminearum is established will largely depend on the occurrence of moderate temperatures and suitable moisture just prior to and during the early stages of flowering.”

Although too late to spray this year, Alberta Agriculture and Forestry and the Alberta Wheat Commission have deployed an online weather-based risk assessment tool for producers to use at the flowering stage to assess if moisture and temperature conditions are conducive for FHB development. "Again, once symptoms are present it is too late to apply a fungicide, but you can still use this information to plan for subsequent growing seasons," says Whatley.

For more information, call the Alberta Ag-Info Centre at 310-FARM (3276).

Contact:
Alberta Ag-Info Centre
310-FARM (3276)

 
 
 
 
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For more information about the content of this document, contact Neil Whatley.
This document is maintained by Ken Blackley.
This information published to the web on July 20, 2017.
Last Reviewed/Revised on July 24, 2017.