Grain head diseases in cereal crops are critical to pay attention to as they can cause significant yield loss and lower the quality of the seed. Some pathogens, including Fusarium head blight (FHB) and ergot, are also highly toxic to both humans and livestock.
Many of the head diseases covered in this blog are also known as seed-borne pathogens. Seed-borne pathogens can survive on or within the seed. This infection can cause disease in the seed itself or the developing plant and potentially lead to further infection in the field. If these diseases are not managed properly infection can compound each year if environmental conditions are favorable. This is especially important to be aware of if you are practicing seed saving strategies.
Common Head Diseases of Grain
Fusarium Head Blight (FHB) aka Scab, Pathogen: Fusarium graminearum
Affected crops: Wheat, barley, oats, rye, triticale, and grasses
FHB is one of the most problematic diseases in the Northeast. Not only does the pathogen cause both yield and quality loss, but under favorable conditions it can cause a mycotoxin called deoxynivalenol (DON). Consumer grains contaminated with 1 ppm or higher can pose a significant human health risk and are restricted from use in food products. High rates of DON can also affect livestock health as well.
Fusarium spores can survive on plant material, soil, and seed, as well as be carried on air currents or by rain splash. The pathogen prefers wet, humid, and warm weather. Wheat is more susceptible at flowering, while barley is more susceptible at heading.
Symptoms in the field can include bleaching on the grain spike while the plant is still green, around the milky ripe stage and salmon-colored spores may be visible on infected spikelets. Infected seeds appear shriveled with a tint of pink. A seed lot sample should be tested as fusarium infection has little correlation to DON infection and could still be over the threshold even if little is seen. Mixed management practices are needed to reduce potential infection. There are some resistant varieties, rotate crops and avoid planting where host crops were the previous year (corn and small grains). Tilling and burying residue can reduce the spore population, along with staggering planting dates which can help minimize a widespread infection.
Ergot, Pathogen: Claviceps purpurea
Affected crops: All cereal and a wide range of grasses, but most serious in rye
Ergot is an easily identifiable disease on grain as the overwintering structures, known as sclerotia, replace the kernel with a large, up to 2 cm, black sclerotium. Ergot is not a true seed-borne pathogen, but it can be spread through a contaminated seed lot or sclerotia that fell off into the field during the previous grain harvest. Spores can be carried in the wind and infect spikelets during flowering. Sclerotia can survive for 1 year on the soil surface so rotating out of a susceptible host is recommended for that time as well as purchasing certified clean seed.
Ergot can be toxic to humans and livestock, causing vomiting, hallucinations, gangrene, muscle spasms, restricted blood flow, loss of extremities, and in some cases can be fatal. Rye crops should always be tested before consumption.
Loose Smut, Pathogen: Ustilago spp.
Affected crops: Wheat, barley, oats
Loose smut can be a devastating seed-borne pathogen causing significant yield loss if widespread. The Northeast is highly susceptible to this disease as it prefers cool, damp conditions and is easily dispersed through the wind. The pathogen resides within the seed and is not visible to the naked eye. At head or spike emergence, diseased heads will emerge slightly earlier than non-infected plants. The heads will appear as a dark brown mass which is covered by a thin membrane. Once healthy plants begin flowering, the membrane ruptures and the spores are blown onto heathy plants to cause further infection. Smutted head has little to no grain.
Planting certified disease-free seed can reduce the risk of loose smut. Research is currently underway to test the efficacy of aerated steam and ozone to control disease in organic systems.
Black Point, Pathogen: Bipolaris sorokiana
Affected crops: All cereal grains, wheat and barley are most affected.
Bipolaris sorokiana is a fungal pathogen that can cause multiple diseases. Mycelium and spores can survive on soil and crop residue. Associated diseases with this pathogen include common root rot, spot blotch on leaves, and black point on grain heads. Black point can occur when rain or excessively humid events occur at grain fill and drying, as this weather allows for the fungal spore to penetrate the grain head and kernels. Black point causes the tip of the grain kernels to become discolored and blacken, unfortunately it is only noticeable after harvest. This disease can affect milling quality and may lead to poor flour, poor bran color and possible rejection. It is recommended to plant clean, disease-free seed as well as rotating out of a field that had a high incidence the year before. Choosing varieties that are adapted to the geographic area could help to limit infection and there are some varieties that show resistance.
Glume Blotch, Pathogen: Parastagonospora nodorum
Affected crops: Wheat, barley, rye
Glume Blotch can become a more serious disease in years with heavy rain fall and warm temperatures that accompany extended humidity. The pathogen can overwinter on seeds, stubble, crop debris, wild grasses, autumn-sown crops, and volunteer plants. When environmental conditions are favorable infection occurs at flowering, grain heads will become bleached accompanied by a brown/purple discoloration. Once developed the grain heads can shrivel, which decreases the grains test weight. It is important to use certified disease-free seed and clean equipment to minimize contamination. Rotating crops to a non-host crop can help to mitigate the risk of infection if it was noticed in your crop.
UVM Extension NWCS: Looking for organic grain samples for disease survey
UVM Extension Northwest Crops and Soils Program is conducting a multi-state grain disease survey to better understand the presence of seed-borne diseases in U.S. grain. If you are interested in submitting a sample to help this research effort and to learn more about what is affecting your crops, please read our Organic Seed Health Survey Letter and to submit a sample click here for the form. If you have any questions, please reach out to Heather Darby (Heather.Darby@uvm.edu) or Kellie Damann (Kellie.Damann@uvm.edu) for more details.
Resources
E.E. Cummings Crop Testing Lab
FDA Deoxynivalenol (DON) Guidelines