By Chaunce Stanton
Farmers plant barley, oats, wheat, and other small grains as early as possible in the growing season to maximize yield potential for grain or forage. Beginning in March, we get the occasional calls from farmers asking why they “couldn’t plant some barley into last year’s corn”.
The simple answer is because of disease.
What’s Lurking in Your Corn Residue?
Corn residue is a host for the fungus Fusarium graminearum, an economically damaging disease that can lead to Fusarium head blight (FHB, also known as scab) in small grains (primarily in wheat and barley, but oats and spelt are also susceptible).
FHB affects grain head development, resulting in 50 percent yield losses some years, but yield loss is only part of the story. Fusarium graminearum can damage grain quality, reduce test weight and lead to poor germination. But more importantly, the disease produces mycotoxins, including deoxynivalenol (DON) or vomitoxin, which can sicken animals (especially pigs) fed the contaminated (“scabby”) grain. Vomitoxin may accumulate at high levels in harvested grain and may cause vomiting and feed refusal if is consumed by livestock. The feed, food, and brewing industries are keenly aware of DON levels and will reject grain with high levels of infected kernels.
A Fusarium infection can work in combination with other pathogens to create complex diseases in future crops, other than small grains:
- Corn: ear, stalk, and root rots
- Forages (including alfalfa and clover): root-and-crown rot complex
- Soybeans: seed rot and damping off
And it’s not just corn fields where you should avoid planting small grains. Fusarium can be found in plant debris (like corn residue), but it can also develop on forages (like alfalfa), and also in other grass species, like foxtail, quackgrass, crabgrass and bluegrass. Those “weed” grasses, in turn, can help spread the infection farther afield, so avoid fields with high populations of grassy weeds, like wild oats, or anywhere you see evidence of a fusarium infection.
No small grain varieties are completely resistant to FHB, but some varieties demonstrate better tolerance than others. While oats are less susceptible to scab than barley or wheat, they can be infected and serve as a host for the pathogen.
Each year, the University of Minnesota Extension rates wheat and barley varieties for susceptibility to FHB. Oats in the U of MN trial are not rated for resistance to fusarium (scab) due to their low incidence of the disease.
Fusarium is moved by wind or rain onto the developing small grains when temperatures are between 65°F and 86°F with high humidity and frequent rainfall. Small grains are most susceptible to infection during flowering and early grain fill when spores of the fungus infect flowering spikes. The resulting grain spikelets infected with FHB “bleach” to a tan or white color, eventually resulting in scabby or shrunken kernels. When conditions are right, the Fusarium fungus may even reproduce spores on the infected plant leaves and stems to spread to non-infected grain heads. The disease can overwinter on infected crop residues like corn, barley, or wheat stubble.
Figure 1. FHB Disease Cycle, from Ohio State University Extension
FHB Management Tips
- Select Resistant Varieties. Although no available varieties of wheat and barley are completely resistant to FHB, select varieties with high resistance ratings, especially when planting in rotation after corn or small grains.
- Rotation Order: Not Following Corn or Small Grains. Crop rotation is an important way to manage the spread and potential impact of the disease. Whenever possible, avoid planting barley or wheat on last-year’s corn or small grains ground.
- Rotation Order: Plant After Non-Host Crop. Planting small grains after soybean or other non-host crop allows the surface residues of corn or small grains from a previous crop year to break down and for the pathogen population to decline.
- Residue Management. Any remaining corn, wheat or barley residue can be a host for future infection, so if you plant wheat or barley on corn ground, minimize crop residue on the soil surface by either baling cornstalk and/or tilling residue into the soil. No-till planting small grains into corn residues substantially increases the chances for FHB infection.
- Bin-Check Seed. Avoid planting bin-run seed that shows signs of FHB infection. Planting infected seed will increase the likelihood of seedling blights and poor stands and could introduce additional inoculum into a crop field.
- Last Resort: Fungicide. For conventional farmers, choosing a fungicide may help limit the spread of the infection, but long-term cultural practices, like those described above, are a better strategy for eliminating a potential environment where FHB can thrive. Even the best fungicides provide only partial control of FHB and vomitoxin levels.
Long story, short: Fusarium is a potentially serious disease of barley & wheat that can be minimized from careful management. Avoid rotations where small grains follow another small grain crop, corn, or weedy fields. Residues of these crops can harbor Fusarium spores, which could infect future crops.
- University of Minnesota Extension: Small Grain Crop Rotations
- University of Wisconsin Extension: Fusarium Head Blight (Scab) of Wheat
- Ohio State University Extension: Fusarium Head Blight or Head Scab of Wheat, Barley and other Small Grain Crops
- Oregon State University: Fusarium Head Blights
- Cornell University: Diseases of Forage Crops
- Montana State University: Fusarium Head Blight (scab) of Wheat and Barley
- University of Nebraska-Lincoln: Stalk and Crown Rot Diseases Developing in Some Corn
- Pennsylvania State University Extension: Fusarium Head Blight
- Top Crop Manager: Staying Ahead of Fusarium Head Blight on Oat
- Manitoba Ministry of Agriculture: Disease and Deficiencies in Forages