Source: University of Illinois

Throughout the Great Plains and the Cornbelt pockets of fusarium fungus are causing wheat scab and threatening to diminish the value of the crop because of the toxins produced. Annually in the U.S. that is a $1 billion problem. Fusarium produces vomitoxin, which is harmful to humans and livestock if consumed in heavy amounts. The wheat itself will have small, shriveled kernels, poor test weight, and can be a health threat to combine operators and others engaged in the upcoming wheat harvest.


Weather conditions have been near perfect this spring for fungal problems in wheat, says Ohio State University agronomist Pierce Paul. He's found both fusarium head scab, and stagonospora glume blotch, both of which create light test weights in wheat. In his latest newsletter he offers photographs, and says stagonospora will cause wheat kernels to be small, but not have the chalky white to pink color that is indicative of scab. He says at high levels, both are capable of causing substantial losses, reducing yield and test weight.


OSU agronomist Pierce Paul and others warn that care should be taken when harvesting wheat with scab infection, due to potential health issues. Their recommendations include the use of a dust mask to avoid breathing in the dust. Use the fan in the combine to eliminate some of the shriveled grain since they are lighter weight. He says that will reduce the grain that lowers quality and creates the vomitoxin. The agronomists also recommend harvesting the infected fields first, since the toxin will increase if the grain is wet prior to harvest. Even if the wheat is harvested at higher moisture levels to halt the deterioration, it will need to be dried below 15 percent moisture to prevent fungal growth and toxin buildup in storage. And they say the wheat must be tested for vomitoxin before feeding it to livestock, as well as making any decision on blending or discarding it.


Regarding the testing for toxins, the OSU agronomists provide recommendations for sampling because grain elevators in Ohio have been testing some of the early fields being harvested. The presence of the toxin will diminish the value if the toxin levels exceed 2 parts per million. For human consumption the threshold is 1 part per mission. If the wheat is being used for ruminant feed or poultry feed, the toxin level should not exceed 10 parts per million. For swine, the limit is 5 parts per million. Additionally, the infected grain should not comprise the entire amount of the feed, but only small portions.


Grain samples should be carefully taken to determine whether the toxin is above or below threshold levels. Agronomist Paul and others say the number of infected heads will vary in a field, subsequently the amount of infected grain will also vary. Authorities recommend samples only be taken by someone wearing a dust mask and goggles and gloves. The recommended procedure is to take 10 to 15 subsamples from the field or the bin. Pneumatic tube samples are not recommended because they will pull more lighter weight kernels into the sample and overestimate the problems.


If you are unsure whether you have the scab problem in your wheat, Penn State University provides a risk tool that is based on whether weather in your area has been conducive for the fungus to spread. The decision aid says, for the week of June 22: "The current focus of the Fusarium head blight prediction effort is on the spring wheat crop in S.D., N.D. and Minn. The spring wheat models have been indicating areas of moderate to high levels of disease risk in some areas of these states this past week. During the last few days, June 20-22, the risk maps are suggesting the risk of severe disease has decreased in all but a few areas. It is not clear at this time if the trend for decreasing risk will continue or if the risk of disease will increase again near the end of the week. Growers in these areas should carefully monitor their local weather forecasts and the commentary of their state extension specialists. If the rain and extended periods of high relative humidity return near the end of the week, the risk of disease may increase rapidly." Additionally, University of Illinois plant pathologist Carl Bradley has produced a You Tube video that indicates what to look for in your wheat.


Nebraska plant pathologist Stephen Wegulo reports that scab spores are abundant during wet weather, and carried by air currents. The spores infect the wheat during flowering because the pollen will serve as a food source for the fungus. And he says it is more severe in reduced or no-till fields and especially if wheat follows corn. As far as managing the problem, the only choices are to plant resistant varieties, rotate fields out of cereal grains, or use a fungicide such as Proline or Tilt during the flowering period.


In the near future, another management tool will be available. Researchers at Ohio State have announced the discovery of yeast that grows naturally on wheat, which will cut the fusarium scab infection by 50 percent, and also reduce the toxin level that it produces. The researchers say it either consumes the food that attracts the fungus to the head of the wheat, or attacks the fungus itself. The yeast is a naturally-occurring product and will be applicable to organic wheat, as well as conventional wheat fields.


Summary:
Wheat scab, caused by the fusarium fungus, has become a predominant problem around the Great Plains and Cornbelt this spring, but it typically a $1 billion annually problem for wheat growers. The fungus produces toxins that reduce the potential for the wheat to be used either as a human food or an animal feed. Care should be taken in the collection of samples, either from fields or bins to determine the extent of the fungus and the toxin. There is no management option that is available once the wheat is past the flowering stage when the fungal spores begin to cause problems.