Proper combine adjustment pays off now and later

You don’t want fusarium-damaged kernels lowering grade or spreading spores, says crop specialist

Producers need to make combine adjustments to prevent kernels damaged by fusarium head blight from going into storage, says a provincial crop specialist.

Harvest management of fusarium-damaged kernels (FDK) will improve the grade of a cereal crop, said Neil Whatley.

“Many FDKs — especially in wheat — are smaller, lighter in weight, and more shrunken than normal, healthy kernels,” said Whatley. “Combine fan speed can be increased to blow out those infected kernels.”

However, this may not be an option for FHB-infected barley and oats where there is less kernel shrivelling, he added.

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“Slower combine travel speed, especially in lodged wheat, also aids in separating good kernels from FDKs by avoiding occasional combine overloads. That ensures an increase in air blast time to reduce FDK level in the grain sample.”

Using a gravity table after harvest can further help with separating lightweight FDK.

“However, producers in areas where FHB caused by Fusarium graminearum is just starting to appear and become established, may want to be cautious about using combine settings to blow out infected wheat kernels,” said Whatley. “The shrivelled kernels tend to be the part of the wheat plant that is one of the most prolific producers of the wind-borne spore stage. It would then represent a higher risk to subsequent crops.”

In areas with a lower risk of FHB, producers can use post-harvest cleaning of grain to remove FDKs to improve grade and reduce the mycotoxin deoxynivalenol (DON), he added.

Additionally, combines should be properly set to thoroughly chop and uniformly spread cereal straw and chaff to encourage better residue decomposition and reduce pathogen survival in a field.

“Remove loose crop residue from harvest equipment before leaving an infested field to prevent spreading the disease to non-infected fields,” said Whatley.

Symptoms of FHB can be seen in harvested grain, especially in wheat. Typically, infected wheat kernels will be shrivelled and have a chalky white appearance with some evidence of fungal growth. In contrast, infected barley kernels do not typically exhibit a lot of shrivelling. Instead of having a chalky white appearance, they will exhibit a brownish discolouration and may show evidence of fungal growth. The brownish discolouration can be easily confused with infections due to the spot blotch fungus (kernel smudge) while hail damage can also produce similar discolouration in barley.

While infection occurring at early flowering can lead to complete abortion of kernels, fusarium-damaged kernels generally result from infection that occurs from the early- to mid-flowering stages. Later infections that occur well after flowering and up to the soft-dough stage of kernel development may not show visible symptoms. However, kernels may contain the fungus, and more importantly, the mycotoxin it produces.

Even if symptoms are not observed when the crop is growing, representative grain samples collected at harvest can be sent to a seed testing lab to determine the level of grain infection by Fusarium graminearum, the most important FHB species, and the concentration of DON. If FDKs are observed in the harvested grain, these can also be tested by commercial labs.

“DON can continue to develop in wet grain, so drying or aerating cereal grains to safe storage moisture contents as soon as possible after combining is important,” said Whatley. “High DON grain should be segregated and monitored while in storage. Prevent moisture migration or rewetting of an area of the bin to avoid further DON development.”

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.

If grain infested with FHB is intended to be used for livestock feed, grain samples should be tested for DON levels through a lab analysis.

“Knowledge of mycotoxin levels will provide guidance as to whether the grain is suitable for feeding, especially for more sensitive animals, such as swine, dairy cattle and horses that tolerate a maximum of one part per million (PPM),” said Whatley. “The maximum tolerated DON level for beef cattle, sheep and poultry is five PPM. It is important to know the amount of DON present (PPM) and then dilute the contaminated grain with healthy grain or forages to lower the amount of toxins to a safe level for feeding.”

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