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Samples Starting to Show up at the Crop Protection Lab

By: Faye Dokken-Bouchard, PAg, Manager, Crop Protection Lab

Types of Samples
Processed at CPL
Number of Samples
as of June 11, 2016
Number of Samples
as of June 11, 2017
Plant Disease Diagnosis 26 19
Weed ID 12 7
Insect ID 2 4
Dutch Elm Disease Testing 10 2

The Crop Protection Lab has received several cereal samples with concerns about viral diseases such as Wheat Streak Mosaic Virus (WSMV) and/or Barley Yellow Dwarf Virus (BYDV). However, only one sample has been confirmed positive using ELISA testing for WSMV. It is important to consider all information and possible causes of yellowing in cereal crops before jumping to the conclusion that it is WSMV.

Reasons why it might be WSMV:

  1. WSMV was confirmed in your cereal crops last season or in neighbouring fields this season.
  2. There is probable history of a green bridge (presence of infected living plants in close proximity to healthy living plants), for example:
    1. Winter wheat seedlings emerged last fall before spring wheat was ripe;
    2. A warm fall, mild winter and adequate snow cover, which allowed the survival of winter crops, grassy weeds, cereal volunteers and the wheat curl mite (vector);
    3. Grassy weeds and volunteers were not controlled before seeding or emergence of a cereal crop; or
  3. There are neighbouring winter wheat and spring wheat fields.
  4. Symptoms of WSMV are present, such as:
    1. Yellow streaking (or yellow and purple, a stress response in durum);
    2. Stunting; and
    3. Curling leaves.
    4. Wheat curl mites (vector of the disease) are present.

Considerations that rule out WSMV:

  1. There was a low risk of WSMV last season (e.g., crop rotation with a pulse or oilseed, or no indication of WSMV in cereal crops last season).
  2. The green bridge was prevented; for example:
    1. There is assurance that spring wheat was ripe or harvested before winter wheat was seeded last fall;
    2. There are conditions likely to reduce the survival of host plants and/or the wheat curl mite vector, such as low snow cover (lack of insulation) or warm temperatures in February and March followed by freezing temperatures;
    3. There is good grassy weed and cereal volunteer control; and
    4. There are no neighbouring cereal crops.
  3. There are indistinct symptoms, such as yellowing, that can also be associated with:
    1. Nutrient disorders such as nitrogen deficiencies;
    2. Abiotic injury such as herbicide damage; or
    3. Environmental stressors. Samples testing negative for WSMV at the CPL this season have largely suffered from environmental stressors such as moisture stress and frost damage
  4. No wheat curl mites or curling of wheat leaves have been observed.

Only samples that are deemed to have a probable likelihood of WSMV or BYDV will be tested with ELISA at the Crop Protection Lab. As always, be sure to include as much field information as possible, along with an adequate sample that includes several “good” and “bad” plants. For ELISA testing, samples must also be as fresh as possible, and not dead (note that viruses don’t immediately kill crops as they require a living host to survive).

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