Features Agronomy Diseases
Watch for clubroot disease in canola this summer

Farmers and agronomists, especially in central Alberta, should scout fields for clubroot.

Dr. Stephen Strelkov of the University of Alberta released the results of the clubroot survey map from 2007 earlier this year. The map shows those areas where clubroot was identified in canola fields in 2007. However, outside of central Alberta around Edmonton, few areas have been surveyed for clubroot, and many more counties in Alberta will be surveyed in 2008 for this disease. As a result, all canola growers are encouraged to look for evidence of clubroot while scouting for other diseases and insects.

Counties where clubroot was identified in 2007. Photo courtesy of Stephen Strelkov, University of Alberta.

What to look for
Clubroot is a soilborne disease and was added as a declared pest to
Alberta’s Agricultural Pest Act in April of 2007. Warm soil (20 to 24
degrees C), high soil moisture and acid soils with a pH of less than
6.5 are favourable to infection and disease development.

Information for Alberta Agriculture provides tips on proper clubroot
identification. Clubroot symptoms vary according to growth stage of the
crop when infection occurs. When canola is infected at the seedling
stage, the symptoms include wilting, stunting and yellowing of plants
in the late rosette to early podding stage, but can look like heat
stress or other diseases such as blackleg or fusarium wilt. To diagnose
the infection, growers must dig up the wilted plants and check for the
tell-tale gall formation on roots.

Infection that occurs at later crop stages may not show plant wilting,
stunting or yellowing. However infected plants will ripen prematurely
and seeds will shrivel. Patches of prematurely ripening canola due to
clubroot infection could be confused with other diseases such as
sclerotinia, blackleg and fusarium wilt. In such cases, proper
diagnosis should include digging up affected plants to check for gall
formation on roots.

If the suspected plants are not sampled until after swathing, the root
galls may have decayed already, and typical whitish galls will no
longer be present. Instead, the decayed galls cause roots to have a
brown peaty appearance rather than a healthy white colour.

A canola root with a severe clubroot infection. Photo courtesy of Kelly Turkington	A canola root with moderate clubroot galls. Photo courtesy of Kelly Turkington
Decaying clubroot galls on a canola root. Photo courtesy of Kelly Turkington	Hybridization nodules should not be confused with clubroot. Photo courtesy of Alvin Eyolfson, Battle River Research Group

Hybridization nodules on canola roots, although rare, could be confused
with clubroot galls, but they appear as small, round nodules located at
root nodes. The interior texture of a clubroot gall is spongy or
marbled while hybridization nodules are uniformly dense inside, like
healthy roots. Furthermore, hybridization nodules will not decay
rapidly to a peaty appearance like clubroot galls do.

If you suspect you have clubroot, talk to your local agronomist and discuss further sampling and identification of the disease.