I first ran into the clubroot disease of crucifers on the farm where I grew up in West Wales. Farmers did not know much about the disease other than it came from purchasing cabbage transplants and it was most destructive on sour soil, a term for acidic soil. Control was stated to involve heavy liming of infested soil, careful inspection of purchased transplants for freedom from clubs on the seedling roots, planting in “clean club-free” land and not planting cabbage, rutabagas or any crucifers on the infested soil for at least four years.
The next time I ran into clubroot was when I was a professor in 1970 on the University of Guelph faculty. One of my responsibilities was the control of turnip mosaic virus, a very destructive disease on the then $60 million Ontario rutabaga industry. I occasionally ran into fields of Laurentian rutabagas that were devastated by clubroot. Eureka, I found one healthy rutabaga in a 50-acre field of Laurentian rutabagas that was big and healthy whereas every other rutabaga was unsalable. Sad to say, this rutabaga was nothing new. It was the variety York, which was resistant to the Group 6 strain of clubroot prevalent in Ontario, stray seed that found its way into a Laurentian seed lot.
- Read more: Clubroot is coming to a field near you
I accepted a position with Alberta Agriculture in 1974 with responsibilities for diagnosing and controlling diseases in canola and cereals. This position gave me more contact with famers, paid more than Ontario and housing was way less costly.
I did lots of field work on sclerotia on canola, seed treatment of canola and worked on smuts and bunts in cereals. I was able to show the effectiveness of systemic seed treatments for loose smut control in cereals and the fact that lindane insecticide was indeed systemic in canola seed and that sclerotinia actually produced apothecia.
In 1976, my technician, Rita Stevens and I received at our Alberta Agriculture diagnostic laboratory four or five samples of clubroot-infected cabbage and cauliflower samples from various Edmonton gardens and a farm garden at Ohaton (Camrose), Alberta.
Knowing how destructive clubroot could be to rutabagas (the Argentine canola parent), Rita and I set up a number of experiments to determine the extent of the clubroot infestation at the farm garden infection at Ohaton and the effect on our currently grown Argentine and Polish canola varieties in 1976.
In our growth chamber and greenhouse experiments with this Ohaton clubroot strain we found that this clubroot isolation was very destructive to Polish canola (Candle) and relatively mild with only small nodules on Altex the most commonly grown Argentine canola. I forwarded samples of the clubroot to a specialist in Quebec who identified the clubroot as Race 6, different from the Race 3 that is presently highly destructive on Argentine canola.
I gave several provincial and at least one national presentation on the danger of clubroot to Canada’s canola industry. I provided photographic slides to several publications including the Western Committee on Plant Disease Control over the following 20 years.
In 1988 I published a write-up on clubroot in the Alberta Text Book Practical Crop Protection. In that one-page deposition I described the biology of clubroot (Plasmodiophora brassicae) and the destructive damage that could be caused by this soil-borne disease. I even described the difference between hybridization modules and 2,4-D damage that caused swelling of the upper root region of the canola plant.
I included a clubroot management strategy from cleaning machinery, drainage of wet soils and liming of acidic soils and other pertinent control facts.
I approached the canola industry in the 80s and 90s for funding to conduct surveys for this destructive disease but came up empty handed.
Eureka! In August of 2003 I got a call from Dan Orchard, then an employee of Sturgeon Valley Fertilizers, asking me to look at a suspected clubroot disease problem in canola near Morinville, Alberta. Dan Orchard, now with the Canola Council of Canada, was correct. It was a field of Argentine canola heavily damaged by clubroot from one end to the other. That summer Dan found 12 more clubroot-infested fields. In subsequent years I checked many fields in the Edmonton area near oilfield pumping equipment. Half of these pump sites that I visited (six out of 12) had clubroot-infected canola around the truck traffic margins of the pump sites.
These earlier findings are now history and canola growers must now face the reality that their most profitable field crop that they grow is now in grave danger.
An ounce of prevention
Clubroot infestation of cropland is not inevitable in fact it’s just about totally preventable. Look at the preventative programs that have succeeded in Canada — ringrot control of potatoes and golden cyst nematode of potatoes, both very destructive diseases. Rat control and Dutch elm disease control in Alberta — neither are present in the province.
How can you exclude clubroot from your cropland?
First of all, clubroot as we now know it is a highly destructive disease of most if not all crucifers, i.e. member of the cabbage family. They include crops such as cabbage, turnips, broccoli and kale, and weeds like wild mustard, stinkweed, shepherd’s purse and volunteer canola. A single large club on an infected canola plant can have as many as 16 million spores.
Here are seven tips for stopping clubroot infestation:
- Check any and every field that you farm for clubroot. Check the canola crop, volunteer canola and any cruciferous weeds (wild mustard, stinkweed, shepherd’s purse) for root infecting clubs.
- Pay particular attention to field entrances. Nine times out of 10 this is where clubroot shows up since it’s where farm machinery, pick-up trucks or any custom farm equipment drops clubroot-infested soil.
- First you must plant clubroot resistant canola. This precaution should prevent clubroot from establishing on your cropland even if you get contaminated by chance.
- If your soil is acidic, i.e. between pH five to seven ,then you should drop a ton or so of crushed limestone on the half acre field entrance. This in time will raise the pH to seven or a little more. Do this to all your canola cropland. High pH does suppress clubroot infection. You may have heard that if your soil is above pH seven you are immune to clubroot. Coffee shop gossip. A higher pH, especially seven and up, will slow down but not stop clubroot. In a wet season clubroot can be destructive even on soil with pH above seven.
- Ensure that any custom seeding or harvest equipment is steam cleaned before access to your cropland.
- Ensure that any utility or oil service equipment that has access to your cropland is steam cleaned prior to access.
- Any new utility equipment that intends to dig its way across cropland should be held to rigid procedures of cleanliness.
If clubroot, Race 3 or another race, has been confirmed on one or more of your canola fields, do not panic. Just follow the procedures for clubroot prevention. Work all of your clubroot-free land first, then seed anything but canola on these infested fields. After working these infested fields either steam clean or thoroughly wash down the equipment that you used for these clubroot fields on your farm yard or on non-crop areas.
If you have total clubroot infestation on most, if not all, of your cropland, you are in a bind.
In this situation, you must use resistant cultivars and depending on location you must follow the advice and directions of local service boards. You must be familiar with the resistant canola varieties available. There are purportedly three kinds of resistance. You must abandon the practice of wheat/canola/wheat/canola or even as some growers do canola/canola/canola. If you persist with this practice, in a very few rotations resistance to the clubroot organism will break down and your canola crops will fail. You will get into significant crop loss.
At best you can grow clubroot-resistant canola once every three to five years in infested croplands. Anything more frequent will in a few rotations make growing a profitable crop of canola impossible.
Clubroot awareness procedures
- Be aware of the potential for clubroot, whether your land is infected or not.
- Be aware of your nearest clubroot infested cropland.
- Ensure that you plant only clubroot-resistant seed varieties.
- Any visitors to your cropland, especially canola crops, whether friends, consultants or commercial industry representatives should be invited to don plastic over boots.
- If you cannot get plastic over boots, prepare a tray of water with 10 to 20 per cent bleach (one part bleach to nine parts water). Ask you guests to step into the tray of bleach for clubroot sterilization.
Following this awareness procedure will focus attention on this destructive disease. Do not worry about what your neighbours might think. You do not want to lose a bundle of money on the best of your cash crops.