How to Identify Virus Infected Fields

Common symptoms of different wheat viruses look identical and are often mistaken for abiotic stresses such as drought and nutrient deficiencies. These symptoms include mosaic or yellowing of the leaves (Figure 1) which can lead to necrosis and stunting of infected plants.

WSMV foliar symptoms

Figure 1 (Jacob A. Price, Charlie M. Rush, and Ron French)

WSMV foliar symptoms

Figure 2 (Jacob A. Price, Charlie M. Rush, and Ron French)

During early infection, symptoms may not be easily visible and plants may have a yellowed appearance gradually developing into a mosaic pattern (Figure 2). Laboratory testing is required for proper identification.

WSMV foliar symptoms

Figure 3, left and Figure 4, right (Jacob A. Price, Charlie M. Rush, and Ron French)

During mite-vectored virus infection, wheat curl mites move into fields by winds from areas of volunteer wheat and perennial grasses which serve as a green bridge for over-summering mites. As the mites transfer these viruses during feeding, they create a disease gradient that often begins on the edge of the field and moves inward decreasing in disease severity (Figure 3). These gradients are not always easy to see but will increase in severity as the season progresses (Figure 4). Aphid-vectored viruses create circular patterns in infected fields.

Texas High Plains Plant Diagnostic Laboratory Form

Plant samples can be submitted to the Plant Diagnostics Clinic at the Texas A&M AgriLife Research center in Amarillo, Texas for virus testing. For complete field testing samples of symptomatic tissue, including roots, collect from the north west, south west, north east and south east areas of the field. A Plant Diagnostic Form should be included with the samples.

The following information should be included on the diagnostic form:

  • Name of field owner
  • Address including county
  • Contact number
  • Information about the field and location (GPS if possible)
  • Any and all information included in the diagnostics form will be helpful in determining disease diagnosis

Sample Submission Guidelines

The Plant Diagnostics Clinic at the Texas A&M AgriLife Research center is a service to the people of Texas by the Texas AgriLife Extension Service and Texas AgriLife Research, in conjunction with Texas Tech University and the Department of Plant Pathology and Microbiology at Texas A&M University. The Clinic is open from 8:00 am – 12:00pm & 1:00pm-5:00pm Monday-Friday (except holidays) and is located at the Texas AgriLife Research and Extension Center.

Samples should be submitted to:

Texas Plant Diagnostic Clinic (TPDC)
Texas AgriLife Research and Extension Center
6500 Amarillo Blvd W
Amarillo, TX 79106

Phone: 806-677-5600 Fax: 806-677-5644

Managing mite vectored viruses of wheat

  1. Volunteer wheat and other grass hosts serve as a green bridge for the wheat curl mite, which and are blown by winds into wheat fields during the fall and spring transferring the viruses during feeding. Due to the small size of the wheat curl mite, scouting for infestation is impossible and producers usually do not realize infestation has taken place until symptoms of virus infection appear in late March to early April.
  2. Producers commonly mistake virus symptoms for other abiotic stresses such as drought and nutrient deficiency causing them to increase inputs such as fertilization and irrigation. During infection, these pathogens not only reduce grain and forage yields but also reduce the plants ability to uptake water from the soil. This is of particular importance in irrigated agricultural systems where the cost of irrigation is high and water resources are low. Therefore, management and detection of these diseases before and after infection is of great importance.

How do I reduce my risk of virus infection?

There is no one way to reduce the risk of infection and multiple methods must be used together in an integrated system. Most importantly destroy all volunteer wheat at least two weeks before planting.

  • Plant late whenever possible.
  • Use mite and virus resistant cultivars: TAM 112 has been found to have good resistance to the wheat curl mite. Virus resistant cultivars such as RonL and Mace have temperature sensitive resistance and must be used in conjunction with late planting only when temperatures remain below 75° F.
  • Early detection of infection – samples can be submitted to the Plant Diagnostics Clinic at the Texas A&M AgriLife Research and Extension Center in Amarillo.