Assessing Fusarium risk now assists with control measures next year
By Alberta Agriculture and Forestry
July 28, 2015 - An Alberta Agriculture and Forestry specialist says there are steps growers can take today to help prevent the spread of Fusarium head blight (FHB) in next year's crop.
"Fusarium head blight is an aggressive fungal disease of cereal crops that affects kernel development and is well established in southern Alberta with trace amounts found in the central and northern regions of the province," says Neil Whatley, crop specialist, AAF, Stettler.
While caused by one or more species, Fusarium graminearum (Fg) is considered the most important FHB species due to its aggressiveness and production of a toxin called deoxynivalenol or DON. DON affects livestock feed, the baking and milling quality of wheat and the malting and brewing qualities of malt barley. The Canadian Grain Commission allows very little Fusarium damaged kernel (FDK) tolerances in top grades.
Whatley says farmers need to use a combination of disease prevention strategies throughout the growing season. "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 Fg 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 maturing cereal crop during heading stage, typically during the last part of July or early August. The most apparent Fg disease symptom is premature bleaching of one or more infected spikelets in the cereal plant's head, which visibly stands out on green heads. Spore growth appears as an orange or salmon coloured fungal growth at the base and edges of the glumes on these blighted head parts.
Whatley says that 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 typically chalky white, 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. While infection occurring at early flowering can lead to complete abortion of kernels, FDKs generally result from infection later in the flowering stage. 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.
Whatley recommends that if any symptoms are observed, to send the affected cereal head samples to a lab to determine whether the Fusarium species is indeed Fusarium graminearum and to determine Fg prevalence. "Routine testing of harvested grain and seed intended for planting is another way of assessing the presence and extent of Fg, especially if harvested grain is downgraded due to the presence of FDK. Several private seed company labs offer testing services for Fg in cereal seed/grain," he says.
"Realizing whether a specific field is a candidate to apply an Fg control strategy is contingent upon the knowledge gained by observing disease symptoms at the heading stage of cereal crops during previous growing seasons. Determining the FHB species and disease severity are the first steps to determining whether a control strategy is necessary," he adds.
Ultimately, Whatley says, determining the need for a fungicide application in an area where Fg is established will largely depend on the occurrence of moderate temperatures and suitable moisture just prior to and during the early stages of flowering. "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."
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