HomeMy WebLinkAboutWSMV alert_30-Jun-2023
Classification: Protected A
Wheat Streak Mosaic Virus infections in Southern Alberta, 2023
Wheat streak mosaic (WSM) is a disease caused by the Wheat streak mosaic virus (WSMV). The virus is
vectored by the movement and feeding of the wheat curl mite (Aceria tosichella). Infected plants are
usually stunted and produce fewer seeds, which are often badly shriveled. The earlier the infection, the
greater is the effect on the plant. Plants may die, fail to set seed, be stunted or show little effect
depending on when they were infected.
Most years the virus and vector do not survive winter, so we do not often see early season symptoms in
Alberta wheat fields. The most recent epidemic in Alberta was in 2017. In 2022, more than ten fields
were confirmed in southern Alberta. As of the end of June 2023, close to twenty fields are confirmed.
The area currently reporting symptoms is south of the Red Deer River.
Scout for symptoms
Producers, agronomists, and crop scouts are encouraged to watch for symptoms of WSMV on wheat
(winter, spring, durum), barley, corn and all other cereals and grasses. Wheat is by far the most
susceptible host, followed by barley, so these crops are most likely to have symptoms. Once wheat or
barley becomes infected, symptoms may appear within a few days.
Initial symptoms include light green streaks parallel to leaf veins that discontinuously elongate to give a
mosaic coloration often alternating between chlorosis, pale green, and dark green. In severe cases
symptoms coalesce to form chlorotic areas and may even cause complete scorching and desiccation of
leaves. On some hosts, a purple discoloration may appear. Symptoms may first appear at the field edge
on volunteer wheat, or on winter wheat crops. At later stages, infected plants may become stunted,
discolored (lemon yellow) and rosetted. If infection occurs before jointing, it can severely reduce or even
prevent grain formation.
Get a laboratory confirmation
It is not possible to consistently diagnose WSMV infections based on the mosaic symptoms found on the
leaves because these symptoms vary with the growth stage of the host, the virus concentration, and will
often overlap with symptoms of other infections or deficiencies. As a result, laboratory confirmation
using a molecular test is recommended. If you would like a sample assessed to confirm WSMV’s
Classification: Protected A
presence/absence , the Alberta Plant Health Lab is temporarily accepting samples. Please contact the
APHL (AF.PHL@gov.ab.ca) for collection and submission/shipping information.
Management of WSM
The only in-season management option for severely infected fields is to harvest the crop early for silage
or green feed. No in-season pesticides or other products exist that can manage WSMV. Fungicides do
not kill a virus, and insecticides do not kill the mite. Miticide spray applications are ineffective because
the mites are microscopic and reclusive – so they “hide” in crevasses, cracks or the underside of leaves
to avoid contact with the miticide. If severe infections occur early in the growing season, it may be best
to terminate the crop and reseed with a short-season broadleaf crop.
The best way to control WSMV is crop rotation and the prevention of “green bridge” hosts. “Green
bridge” is a term referring to continuous green tissue available for the virus which provides a vector to
“bridge” the spring crop to the fall-seeded, or winter, crop. The virus and vector cannot survive for more
than a week or two without a green host. Preventing a “green bridge” will break the disease cycle and
eliminate the problem for the next growing season. This is accomplished by controlling/managing cereal
volunteers and (most importantly) by delaying the seeding of winter cereals for at least two weeks after
harvest of the spring-seeded crop. This will create a two-week period with no green host tissue available
to support WSMV’s survival. The result is that both the virus and mite vector die, and there is no bridge
to the next growing season. Winter wheat and other fall-seeded cereals can still be grown, but delayed
seeding is essential. Finally, a two-or-more year break between cereals is recommended.
More information
https://open.alberta.ca/dataset/479eefac-42ad-4cc7-8ece-f2b40125b267/resource/eac60351-b802-
464a-9b53-10fa826219e3/download/1993-112-632-3.pdf
https://www.montana.edu/extension/judithbasin/documents/montguides/Cereal-viruses-importance-
mt-montguide.pdf
Contact:
Dr. Michael Harding, Crop Health Assurance Lead, Alberta Agriculture and Irrigation
(michael.harding@gov.ab.ca)