Avoiding Viruses in Small Grain Crops

We don’t often think of viruses first when diagnosing issues of small grains, but viral diseases can become problematic in some fields. Here are some of the more common viruses in our region’s crops (click on the links to learn more about each):

Barley Yellow Dwarf Virus (BYDV)

• Affects: Barley, wheat, oats, triticale
• Symptoms: bright yellow leaf tips (barley), purplish-red leaf tips (wheat, oats), stunting
• Spread by: aphids

Wheat Soilborne Mosaic Virus (WSBMV)

• Affects: Barley, wheat, triticale, rye
• Symptoms: yellow-green mottled leaves or streaking, stunting
• Spread by: a fungus-like soil-dwelling organism

Wheat Streak Mosaic Virus (WSMV)

• Affects: Barley, wheat, triticale, rye, oats
• Symptoms: yellow mosaic streaking, stunting
• Spread by: leaf curl mite

Diagnosis

If you suspect a virus issue in your small grains consult with an extension educator and get a sample tested. Diagnosis is the first step to forming a management plan to preserve future crops and forage. Your specific management approach will depend on which virus(es) are prevalent in your fields.

Because viruses cannot be viewed with a typical microscope or readily grown in a lab, they are difficult to detect using the methods available in many plant diagnostic clinics.  Serological tests (similar to rapid virus tests for humans) exist for many plant viruses but are rather costly and expire quickly, making it challenging for a clinic to keep them on hand for all potential viruses on all potential crops.

Because of this, we recommend that you work with an extension professional to identify the most likely pathogens in your case. Using this information, appropriate samples may be sent to a private testing lab (e.g., Agdia), and you can request one or more screenings for your crop. There is a cost associated with this type of testing, so it is important to narrow down the potential culprits for screening and prepare the best possible sample to send.

Strategies for management

Once a viral issue is detected in a field, there is little that can be done to manage that season’s crop. However, steps should be taken to mitigate the effects on future crops. Many of our common viruses are avoided by investing in the following:

Clean seed

High-quality seed is the first input for successful crop production. Using certified seed ensures varietal purity, optimum seed health, uniform and fast germination, reduced number of weed seeds in the seedlot, and minimal risk for the introduction of noxious weeds in your fields. The high-quality standards of certified seed are obtained during seed production through phytosanitary inspections and strict disease and weed control.

Many viruses are seedborne and will survive seed processing stages like sorting, cleaning, drying, and storage. Planting saved seed increases your chances of having a future crop with disease issues. Never save and replant seed from a crop with suspected disease infection.

Variety selection

Once you have a diagnosis, work with your seed dealer to identify varieties with some resistance that will also provide the agronomic characteristics you need. This information is not usually readily available in seed selection guides, so your seed representative may need to reach out to their breeders to find the information you need.

Green bridge elimination

Our small grains crops are typically infected in the fall, even though most symptoms are not visible until months later. This is because the vectors (organisms that transmit the virus) are abundant, active, and able to pick up viruses from grassy weeds, volunteer grains, and small grain cover crops, and transmit the virus(es) to freshly emerged fall-planted seedlings. The earlier a new grain crop is planted, the greater the chance that vectors can move the virus from currently infected plants to your emerging crop. This is called the “green bridge,” and allows the virus (which can’t survive outside a host or vector) to be transmitted from infected mature crops to newly emerged plants.  Breaking the green bridge is critical to slowing the spread of BYDV and WSMV in particular because of their insect vectors. Delay of fall planting (corresponding to the Hessian fly-free date) is recommended to prevent the transmission of viruses, and the elimination of grassy weeds and volunteer plants nearby is critical.