Growers have been repeatedly alerted to the dangers of clubroot by scientists, government and industry. This disease has been written about extensively in most farm publications and even discussed in mainstream media. There is a huge amount of information available online about clubroot, including management strategies to keep it in check.
And yet, clubroot continues to expand its footprint in western Canada. Indeed, at the end of August 2017, another Alberta county reported its first case of clubroot. How much do you really know about this disease? Test your own clubroot knowledge by answering these eight questions.
Clubroot is a new disease: True or False? False.
Actually, descriptions of clubroot-infected crops date back to 13th century Europe. In 1875 Russian scientist Mikhail Woronin identified the plasmodiophorous organism that was causing a clubroot epidemic that wiped out cabbage crops in St. Petersburg. He named it Plasmodiophora brassicae.
Clubroot is just an Alberta problem: True or False? False.
In the fall of 2011 Agriculture Canada confirmed the presence of clubroot in two north-central Saskatchewan canola fields. In 2013, Manitoba Agriculture reported that two canola fields had been identified and confirmed as showing in-crop clubroot symptoms. By 2016, the province had identified five rural municipalities where clubroot symptoms were observed. Harry Brook, crop specialist with Alberta Agriculture in Stettler, says new DNA testing for clubroot in the soil has revealed low levels of clubroot genetic material in soils across the prairies.
Clubroot only affects canola: True or False? False.
Clubroot is a much bigger problem than just a disease of canola. It affects the roots of all cruciferous plants, including field crops like canola, mustard and camelina; cruciferous vegetables such as broccoli, Brussels sprouts, cabbage, cauliflower and kale; and cruciferous weeds, like stinkweed, shepherd’s purse and wild mustard. All cruciferous plants are potential hosts for the disease. And that includes volunteer canola. If you are not controlling volunteer canola as well as cruciferous weeds in rotational crops, you are increasing the risk of the disease in your canola fields.
Clubroot is easy to identify: True or False? It depends.
Early in the year, clubroot can easily be mistaken for root rot, black leg, fusarium wilt or even sclerotinia. Early infection of any of these diseases can result in wilting, stunting and yellowing of canola plants, right up to podding. All of these diseases cause premature ripening and shrivelling of seeds from late infections. So, simply looking at the crop will not confirm clubroot — pulling up diseased plants will. The formation of galls on the roots of the plant is an indicator for clubroot; hence the name of the disease. Another thing to watch for is during swathing when clubroot infected plants are often pulled right out of the ground by the reel or knife due to the deformation of the root. Finally, DNA testing of plant tissue can confirm clubroot. Labs are also able to detect the presence of clubroot in the soil at very low levels; below levels at which clubroot becomes problematic. The seed testing lab, 20/20 Seed Labs Inc. uses a DNA-based test developed at the University of Alberta that can detect clubroot at levels as low as 1,000 spores per gram of soil. It takes 10 to 100 times this level for clubroot symptoms to appear in crop.
There are no chemical controls for clubroot: True or False? True.
Currently, no chemicals have been proven effective or registered for the control of clubroot. Since the clubroot pathogen displays plant, animal and fungal characteristics, it will be very difficult to develop a safe, effective chemical for controlling clubroot. Scientists are investigating bio-controls (bacterial and fungal agents) for controlling clubroot. There is also ongoing research into the effects that soil pH and soil nutrients have on this disease and if the disease can be managed by modifying soil characteristics.
I don’t have to worry, I plant clubroot resistant varieties: True or False? False.
If clubroot resistant varieties had not been developed, canola would not be a viable crop in some areas of central Alberta where the disease has caused significant yield losses since 2003. Unfortunately, the resistance is now breaking down. There are a number of strains of clubroot and the strains found in Alberta are quite virulent. Clubroot is overcoming the resistance faster than the development of new resistance packages. Growers cannot rely on resistant varieties alone; they must follow an integrated pest management program to keep clubroot in check.
You can prevent the spread of clubroot: True or False? True.
Clubroot is a soil borne disease so if you can prevent the movement of soil from field to field, you can prevent the movement of the disease. However this is easier said than done. Cleaning and sanitization of equipment between fields is very important when moving from an infested field to a field without clubroot. This means all equipment, not just tillage and seeding tools must be cleaned as infected soil can be carried on tires and even footwear. You also need to control soil being carried in water run-off from infected fields as well as movement of soil by wind. One solution is to seed clubroot infected areas of fields to grass to limit movement of soil from these areas. Never use seed bin run seed, as even earth tag on seed can harbour clubroot spores.
Rotation to a non-host crop is key to reducing clubroot risk: True or False? True.
There is no question rotation is probably the best management practice for reducing clubroot spore load in the soil. However, the half-life of clubroot spores is four years so if you are growing canola, or any other host crop, more than one year in four you are increasing the number of clubroot spores in the soil. Failure to control canola volunteers in rotational crops is the same as having no rotation and a sure way to increase the risk of clubroot. Furthermore, resting clubroot spores can survive in the soil for 10 to 20 years. So even with a one in four rotation, the possibility of clubroot losses can never be eliminated by rotation alone. It’s sobering to note that research done in Sweden found it took 17 consecutive years of growing non-cruciferous crops for spores to drop to non-detectable levels in clubroot infested rapeseed fields. Essentially if you have clubroot in your fields, the only way to eradicate it is to never again grow cruciferous crops.
Further information: Canola Council of Canada clubroot info: www.farmforum.ca/CCCclubrootinfo
Saskatchewan Ministry of Agriculture clubroot in canola factsheet: www.farmforum.ca/SKclubrootincanola
Alberta Agriculture and Forestry clubroot in canola info: www.farmforum.ca/ABclubrootincanola
20/20 Seed Labs Inc.Alberta clubroot map: www.farmforum.ca/ABclubrootmap