Do You Know DON?Written by Jeremiah Vardiman
No, we are not talking about your neighbor or relative. DON is in reference to Fusarium Head Blight, also known as scab or DON, which is a fungal disease that significantly effects wheat and barley crops. This could be a potential concern to Wyoming’s farmers, who produced 4.75 million bushels of wheat and 6.74 million bushels of barley in 2014.
This fungus attacks the grain of the crop causing yield loss, low test weights, low seed germination and mycotoxin contaminated grain, which results in lost revenues for farmers and potential rejection of the harvested grain at elevators. The main identifying symptom for this disease is bleaching of some florets in the crop’s head prior to maturity, while severe infections can cause premature bleaching of the entire head. Infected kernels often have pink- or orange-colored mold on them and are often shriveled, white and chalky in appearance.
The disease is caused by several species of fungi from the group known as Fusarium, hence the name. Fusarium graminearum is the most common. This disease can be introduced into fields by spores blown in by the wind or contaminated seed. Like most fungi, Fusarium Head Blight thrives in warm moist conditions that can be caused through rain, irrigation, fog and/or long, evening dew events. Therefore, this disease is more prevalent in irrigated fields than dryland. However dryland fields can become infected if climatic events line up correctly.
Once established in a portion of the field, Fusarium Head Blight spreads rapidly throughout the area by wind and splashing water. The most susceptible portion of the wheat and barley plant is the head, particularly when the crop is flowering. After the growing season, the fungus overwinters on crop residue and can re-infect the following wheat or barley crop. It should also be noted that Fusarium Head Blight can also persist and colonize corn and other grass crops such as forage grasses.
Preventing and reducing disease
What can be done to prevent or reduce this disease?
First of all, if there is no history of scab in your fields, neighbor’s fields or county, then the chances of infection are extremely low, and Fusarium Head Blight is probably not a huge concern.
If there is a concern of potential infection, following an integrated pest management (IPM) or multifaceted approach is highly recommended.
Typically the first recommendation for IPM would be to use resistant varieties. Currently there are several spring wheat varieties that are tolerant, though there are no tolerant or resistant barley or winter wheat varieties.
The next management implementation is crop rotation, which breaks the cycle of the disease and declines the fungi population that causes reinfection, especially if a legume crop or broadleaf crop is rotated between grain crops. Research has proven that Fusarium Head Blight infection is two times higher when wheat is planted into wheat stubble than when wheat is planted into soybean stubble.
Research has also revealed that infections to wheat and barley are five to 10 times higher when planted after a corn crop. Wheat or barley crops are also at risk if they are planted adjacent to last year's infected fields.
The next management strategy to implement would be the removal of the grain crop residue. Unfortunately this disease is benefited by soil health practices of residue retention through no till, minimum till and strip till because the residue allows the disease to persist in the environment until the next host crop, whether that be wheat, barley, corn or grasses, can be infected.
Montana’s 2015 malt barley crop saw fairly high infections of fields that were planted after corn. The practice almost guaranteed infection of barley directly planted into corn stubble under a no-till system. Effective means for handling crop residue are burning, burying or complete removal.
Irrigation management can also be used to decrease the potential risk of scab infection.
If possible, time irrigation to prior to and after flowering of the crop. This practice provides adequate water to the crop while leaving a dry microclimate in the crop canopy that is less favorable to the fungi.
Though not necessarily an option to all farmers, it is worth noting that furrow or flood irrigation can provide a slightly drier crop canopy than pivot or areal irrigation and typically does not spread the disease through the splashing of water droplets on infected crop material.
If the prior management practices fail to prevent an infection and an infection is found early enough, then a fungicide is the last option. Fungicides only suppress the disease. They do not kill or eliminate it.
For fungicides to be effective at suppressing the disease, application timing is crucial and should occur at the first sign of anthers extruding from the wheat head or directly prior to barley head emergence. Fungicide products are locally systemic, meaning they only protect the tissue they are applied to and not the entire plant.
The most effective fungicides provide about 50 percent control compared to untreated crops, so do not base full management plan on chemical control.
In summary, if there is no history of this disease in your area, Fusarium Head Blight is probably not a large concern. However, if there is a history, then this disease is controllable with sound management practices.
Fusarium Head Blight needs warm humid conditions during flowering to favor an infection and production. Rotating crops from cereal crops to non-cereal crops will aid in breaking the disease’s life cycle. Removal of cereal crop residue will further aid in breaking the disease’s life cycle. Planting barley or wheat after corn, especially into corn stubble, greatly increases the risk of infection.
Fungicides only suppress the spread and impact of the disease on the crop. It does not kill the fungus.
For more information please contact your local Extension office or industry representative.