The first step in managing clubroot is to minimize the chance of introducing clubroot to the farm in the first place. Make sure equipment and vehicles entering fields are clean. All people entering a field should have disinfected rubber boots or wear disposable booties over their footwear. All seed (not just canola) should be cleaned and treated to prevent introduction of clubroot on dirt tag.
In one case in Alberta this year, the field had been in hay for many years and this was its first crop of canola. But the farmer had broken up the hay using a tillage tool that must have been contaminated with clubroot-infested soil. “Once clubroot is in a field, it can get established quickly in a year like 2017 with good moisture conditions,” Orchard says.
If clubroot is present in a field, take measures to prevent the disease from reaching yield loss levels in future canola fields. To prevent the buildup:
- Grow a clubroot-resistant (CR) variety. Certainly do this when clubroot is confirmed on your farm (either through plant symptoms or soil DNA test). CR varieties are also recommended when clubroot is confirmed or even suspected in your community or region.“If you don’t know whether clubroot is in your area, CR varieties can be a useful prevention tool,” Jurke says. “The risk of using a CR too early and contributing to breaking of the resistance is small compared to the risk from using a susceptible (non-CR) variety early and having the disease escalate quickly to very costly levels.”Even with CR varieties, keep scouting. Clubroot pathotype populations will adapt to resistance sources. Rotation to other CR sources may be required to keep the disease down.
- Control weeds and volunteer canola as these can promote spore buildup in non-canola years in the rotation. Brassica weeds, including shepherd’s purse, flixweed and stinkweed are also clubroot hosts.
- Rotate out of canola for at least two years. “The value of rotation cannot be overstated,” Sekulic says.
- Contain diseased patches as long as possible. Reduce tillage where possible and take measures to isolate affected areas. One method is to seed the patch to perennial ryegrass. This will stop soil movement out of the patch, and a patch left for five years or more will greatly reduce the viable spores left within this patch. Another potential option is adding lime to increase soil pH. Ongoing work shows clubroot-reducing benefits from liming, but further research will determine required rates and whether this could pay off across whole fields.
- Designate separate field entrances and exits. Given that 90 per cent of fields identified with clubroot show symptoms at field entrances first and that these areas tend to be the most heavily infested, having a separate exit means equipment isn’t leaving from the most infested area of the field. This will reduce the amount of spores picked up on the way out. The exit, if possible, should be far away from the entrance and preferably on higher and drier ground.
- Finally, keep watching and keep listening for more alerts and more tips as the collective education builds. “If we learned anything in 2017, it’s that clubroot can be far more aggressive that we expected and spread a lot faster than we dreamed,” Orchard says.