Anyone who moves from field to field has a responsibility to reduce their risk of spreading clubroot (and other pests, including aphanomyces and noxious weed seeds). That means avoiding build up of soil on vehicles and boots and, if the vehicle or boots do get muddy, taking time to remove that mud before moving to another farm.
A few tips:
Make field visits on foot, where possible.
When not possible to visit fields on foot (custom field operations and soil sampling by truck/quad, for examples), try to enter and exit fields from places other than the farmer’s usual entry and exit points. Field entry points are most likely to have higher levels of clubroot, which is why you want to avoid those areas entirely, if possible. This should be particularly easy if entering the field on a quad. And field entrances and exits are excluded when soil sampling for nutrients anyway.
Keep scrapers and wire brushes on hand to clean wheels and wheel wells caked with mud. Portable pressure washers or high-pressure blowers might help. Clean vehicles on a patch of grass beside the field you’re leaving. If necessary, make a quick stop at a local car wash.
Wear different booties for each field or, better yet, set up a simple boot bath. Scrape off any mud before leaving the field, then stick the boots in a disinfecting bath. A large rubbermaid container filled with a 1-2% bleach solution (e.g. 1 part 5% household bleach per 3-5 parts water) or Virkon and a lid with holes for the boot tops works really well for rubber boots. Virkon is available through veterinarian offices and some local farm supply stores.
Use the same 1-2% bleach solution to clean any tools used to dig in the soil.
Talk to your farmer customers about their clubroot situation and their expectations for your equipment cleanliness. Make them aware of the steps being undertaken to limit the spread of clubroot infection.