Spring Wheat Crop May Still be Susceptible to Scab, Vomitoxin

Deoxynivalenol (DON), commonly referred to as vomitoxin, is a mycotoxin that may be produced in wheat infected by Fusarium head blight (FHB) or as it is commonly known, scab. Scab may infect grain heads when wet weather occurs during the flowering and grain filling stages of plant development.

Jochum Wiersma, small grains specialist, University of Minnesota, said in a July 18 blog: "The risk for Fusarium head blight remains moderate to high for highly susceptible varieties for most of Minnesota through the coming weekend. The marked difference in the risk of infection between highly susceptible and moderately resistant varieties remains the same."

Wiersma noted, "Early infections cause the highest yield losses and produce proportionally the highest amount of DON. Fortunately, these early infections produce the shriveled, chalky-white tombstone kernels. These kernels can readily be removed from the sound grain during combining by adjusting the fan speed and the amount of grain on the return auger. The farmer's goal should be to avoid any of the tombstone kernels ending up in the grain tank on the combine. Harvest losses will be higher, but you disproportionally reduce the amount of DON in the harvested grain (henceforth the less robust correlation between the incidence of the disease and DON concentrations in the harvested grain)."

Wiersma told DTN, "For most of the month we have pretty much been in moderate to high risk across most of the state (Minnesota) for highly suspectable varieties and moderate to low risk for moderately resistant varieties. Unfortunately, we have about a third of the acreage planted to varieties in the first category. Some initial reports from producers are there is more FHB than they have seen in a long time. Some estimate the field severities in the 5% to 7.5% [range] with the use of a fungicide. That's a salvageable situation. However, this week's weather will be favorable for late infections across the northern half of the state and that's not good news."

There have also been incidents of scab in eastern North Dakota and the Red River Valley. North Dakota State University noted on their website, "High humidity, rain, dew, moderate temperatures, and ultraviolet radiation affect pathogen survival, spore production, spore spread, infection process, and disease development. Extended duration of high relative humidity is one of the key factors indicating high risk of infection in the current Fusarium head blight model." Here is an interactive map for all North Dakota cities to check if they are susceptible to scab: https://www.ag.ndsu.edu/…

According to Purdue Extension, "The occurrence of scab does not automatically mean that DON is present, however, DON levels can be high even when disease levels are low. If harvested grain has high levels of tombstones or damaged kernels DON is likely present. The mycotoxin can continue to accumulate until grain moisture levels fall below 13%, so DON levels can be very high when wheat is harvested late in the season. Hogs are most sensitive to DON and may refuse to consume DON-contaminated grain, which will result in poor weight gain. DON affects cattle, sheep, and poultry less." https://www.extension.purdue.edu/…

NDSU also reported, "The occurrence of FHB does not automatically mean that DON is present, but a high level of scab kernels in the harvested grain means DON will likely be present. Levels of DON do not necessarily correlate with levels of physical damage in grain. Grain with DON would have to be ingested in very high amounts to pose a health risk to humans, but it can affect flavors in foods and processing performance." Because of that, individual millers or food industries may have stricter requirements than 1 part per million versus the industry standard of 2ppm."

"FHB and the associated DON contamination of the grain, will be an issue for individual producers and the trade as a whole until after all the grain has been marketed and moved through the trade," said Wiersma.

"Let's collectively keep our fingers crossed that, on the 30th anniversary of the 1994 FHB epidemic which made us realize that the previous year's epidemic wasn't just a fluke, this isn't that."

Source: DTN