November 12, 2005
From: Lloydminster Meridian Booster, 11 Nov 2005 [edited]

Clubroot [CR] is a soil-borne disease that affects crucifer crops, including cabbage, broccoli, cauliflower, canola and mustard. The disease is found in many parts of the world. In Canada, it has been a problem for commercial vegetable producers in British Columbia, Quebec and Ontario.

According to Kent MacDonald, P.Ag., CCA, crop specialist with Agriculture Alberta, there were no reported disease problems with canola during 2004. In 2005, however, there were reports of CR in several new fields in the Edmonton area. CR is especially problematic because the fungus persists in soil for many years, and there are no crop protection products currently registered for its use in Canada.

_Plasmodiophora brassicae_ Woronin causes CR. It infects the roots and causes formation of irregular club-like galls. These galls restrict the flow of water and nutrients to leaves, stems and pods.
Plant symptoms include wilting, stunted growth, yellowing, premature ripening and shriveled seed. Plants infected early in the growing season may resemble those suffering from heat or drought stress.
Crops that have finished flowering may express symptoms resembling sclerotinia stem rot or possibly fusarium wilt. In most cases, CR can be diagnosed by a close examination of the root system.

Based on using CLIMEX, a computer software program designed to predict potential distribution and relative abundance of species (insect, disease, etc), the Edmonton region was likely regarded as one of the few areas of western Canada where CR would induce significant economic crop loss. Other Alberta areas with similar climatic conditions still have the potential for CR development and need to be aware of the potential significance of the disease.
Although CR problems are not widespread, the economic impact of the disease can be significant for individual producers.

MacDonald says that canola yield losses from research data indicate that CR infestations are approaching 100 per cent, leading to yield losses of 50 per cent. The percentage of yield loss from CR is generally half of the percentage of infected plants. There is no real cure for CR. The best management strategy is prevention, and that
includes: long rotations (4 years) between canola crops as the single most important preventative strategy. Fields that have CR problems have a history of short (often 1-in-2 years) canola rotations.
Lengthening the canola rotation may reduce profitability in the short term, but the long-term gains will be substantial if the longer rotation prevents CR. Field equipment requires application of phytosanitary measures such as cleaning soil from equipment, including tires; and avoiding hay and straw purchases from regions known to be infested or suspected to be infested with CR because straw and hay could be carrying soil and the CR pathogen.

Once land is infected with CR, management strategies are more difficult and/or expensive. Canola should not be seeded on infected land for 5-7 years. The CR pathogen can survive in soil for up to 17 years, so a 5-7 year break from canola may not eliminate the problem.
The extended rotation away from canola must also include diligent control of species susceptible to CR. Volunteer canola, weeds in the mustard family, dock, hoary cress, orchardgrass, red clover, red-top, and perennial ryegrass will minimize soil erosion with zero or minimal tillage. Since CR is a soil-borne disease, the fungus will move with wind or water-eroded soil. There is evidence that liming soils to pH 7 or higher will reduce the viability and longevity of spores in the soil.

--
ProMED-mail
<promed@promedmail.org>

[CR is a very difficult disease to manage, and heavily infested areas may have to be abandoned for crucifer production. Some control may be achieved with the following measures: use a good crop rotation program, growing crucifers on the same soil no more than every 3rd or 4th year, is essential to retard development of a large population of spores on land not already heavily infested; liming (calcite) soil to pH 7.2 or above may be helpful but avoid raising the soil pH too high so as to interfere with growth of succeeding crops other than crucifers; planting with pathogen-free plants in pathogen-free seedbeds and uninfected plants is essential to prevent introduction of the disease; application of a fungicide in transplant water or rototilled in a band prior to planting may help to reduce disease development; clean and disinfect all machinery before moving it from infested to non-infested land and use resistant cultivars if available, although plant resistance has not been ver!
y useful in CR control because of rapid development of new races of the fungus.

Links:
<http://archives.foodsafetynetwork.ca/agnet/2005/5-2005/agnet_may_13.htm#story5>
<http://res2.agr.ca/stjean/publication/bulletin/plasmodiophora_brassicae_e.htm>
<http://www.apsnet.org/phyto/PDFS/1999/0316-01R.pdf>
<http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex8593>
<http://ohioline.osu.edu/hyg-fact/3000/3118.html>
- Mod.DH]

[see also in the archive:
Clubroot, canola - Canada (Alberta) 20050512.1301]