Clubroot is a serious disease that affects vegetables in the cabbage family, including broccoli, Brussels sprouts, cabbage, cauliflower, kale, and turnips. The disease is caused by a soil-borne fungus called Plasmodiophora brassicae. If left untreated, clubroot can destroy an entire crop. However, with proper identification, treatment, and prevention methods, gardeners and farmers can successfully manage this disease.
Identifying Clubroot
Detecting clubroot early is key to saving crops. Here are the signs to look for:
Wilting and Stunted Growth
The first visible symptoms of clubroot are wilting leaves and stunted growth. Plants will appear less vigorous overall. Leaves may turn light green or yellowish. Wilting often occurs first on hot, sunny days when the plant is stressed.
Swelling and Deformation
As the disease progresses, swelling and abnormal growth will occur on the roots. Look for club-shaped enlargements or “galls” on the roots. Above ground, heads of cabbage or broccoli may be smaller or distorted.
Nutrient Deficiencies
Due to damaged roots, plants will start to show signs of nutrient deficiencies like chlorosis, where leaves turn yellow from lack of nitrogen. Plants may also appear more pale or purple from phosphorus deficiency.
Premature Ripening
Infected vegetables will prematurely “bolt” or go to seed. Heads of cabbage and broccoli will be loose instead of tight. Caution: Other factors like heat can also cause premature ripening. Clubroot may be one contributing factor.
Reduced Yields
As plants decline, yields will be significantly reduced. In severe cases, clubroot can wipe out an entire crop. Lower yields may be the first sign that clubroot is present.
Carefully dig up and inspect roots if clubroot is suspected. Look for swollen galls and deformities. The fungus resides in the soil, so symptoms may appear in patches of plants rather than isolated individuals. Scout the whole garden or field to assess the severity. Send suspicious root samples to a diagnostic lab for confirmation.
Treating Clubroot Infestations
Once clubroot is confirmed, action must be taken to avoid spreading the infestation. Here are treatment methods to try:
Quarantine Infested Areas
Cordon off areas where clubroot symptoms are identified. Disinfect tools after working in affected soil. Wash boots and gloves before going elsewhere in the garden. Avoid tracking contaminated soil to clean areas.
Solarize the Soil
Solarization uses the sun’s heat to kill pathogens in the soil. First, moisten the soil and cover it tightly with clear plastic sheeting. Leave the plastic in place for 4-6 weeks during hot, sunny weather. The soil heat under the plastic can reduce resting spores.
Adjust Soil pH
Clubroot thrives in acidic soil below pH 6.5. Test soil pH and add agricultural lime as needed to raise the pH above 7.0. This reduces but does not eliminate the pathogen.
Rotate Crops
Avoid planting brassica family crops in infested soil for at least 2-3 years. The clubroot fungus will decline over time without host plants. Rotate to unrelated crops like corn, beans, or onions which are immune to clubroot.
Add Resistant Varieties
Some broccoli, cabbage, cauliflower, and other brassica varieties have genetic resistance to clubroot strains. Check with local extension services for resistant seed recommendations for your region.
Apply Fungicides
Certain fungicides may suppress clubroot. Products containing fluazinam have shown effectiveness. Soil drenching and repeated foliar applications are needed for control. Always follow label directions.
Remove Severely Infected Plants
Pull out and destroy any plants with advanced clubroot. This prevents them from contaminating the surrounding soil. Do not compost diseased plants.
A combination of these treatment methods is required to manage existing clubroot infestations. Start treatment as soon as symptoms appear to limit losses.
Preventing Clubroot Outbreaks
Prevention is always preferable to treating clubroot once it occurs. Here are some key prevention strategies:
Test Garden Soil
Have soil tested to determine pH and check for clubroot resting spores. This allows preventative steps to be taken proactively before infection occurs.
Raise Soil pH
For brassica crops, make sure soil pH is maintained between 6.5-7.5. Liming acid soils suppresses clubroot spore germination.
AvoidIntroducing Contaminated Soil
Thoroughly clean any tools or equipment that may carry clubroot before bringing them onto your property. Only use clean soil, compost, or manures from reputable sources.
Use Sanitized Containers and Trays
Disinfect seedling containers, trays, and greenhouse benches. Use a 10% bleach solution or other sanitizer labeled for horticultural use.
Rotate Plant Families
Follow a 4-year crop rotation plan for brassicas. Do not grow them repeatedly in the same location. Rotate to non-host plants like legumes, grains, and grasses.
Scout for Early Symptoms
Carefully inspect young seedlings and transplants. Rogue out any plants showing clubroot symptoms. Send samples for testing if unsure.
Choose Resistant Varieties
When available, select brassica varieties labeled clubroot-resistant. Check for resistance to strains identified in your area.
Install Raised Beds
Growing in raised beds allows for new, clean soil. Use an artificial soilless mix in severe cases. Avoid planting in infested in-ground soil.
Staying vigilant for early warning signs, testing soil, rotating crops, and selecting resistant varieties are your best defenses against clubroot. Careful prevention protects garden and field brassica crops.
FAQs About Clubroot Identification, Treatment, and Prevention
Here are answers to some frequently asked questions about dealing with clubroot:
How do I sample soil to test for clubroot?
Collect soil from the root zone of plants. Sample multiple areas and combine into one composite sample. Send one pint of soil to a diagnostic lab to be assayed for clubroot DNA.
What vegetables get clubroot?
Clubroot mainly affects crops in the brassica or cabbage family like broccoli, Brussels sprouts, cabbage, cauliflower, kale, and turnips. Other cruciferous weeds can also be infected.
How long does clubroot last in soil?
Resting spores can survive in soil for up to 20 years without a host plant. The disease is very persistent, but the spore population will decline over time when rotations avoid brassica crops.
Is clubroot deadly to plants?
Yes, clubroot can be fatal if severely infected plants are not removed. The disease progressively blocks water and nutrient uptake through the roots eventually killing the plant.
Can I plant brassicas in infected soil?
It’s best not to plant brassicas in soil where clubroot has occurred for at least 2-3 years. Longer rotations of 4 or more years are better. Grow alternate non-host crop families.
Are clubroot galls edible?
No, any swollen galls on roots should not be eaten. The deformities contain the clubroot pathogen. Only consume vegetables showing no clubroot symptoms.
Can clubroot affect my other garden plants?
No, clubroot only infects members of the brassica family. Unrelated plants like tomatoes, beans, lettuce, and onions will not become infected.
How do I sanitize tools and equipment?
Clean tools and equipment with a 10% bleach solution after exposure to infested soil. One part bleach mixed with 9 parts water is effective. Rinse after 10 minutes.
Where does clubroot come from originally?
Clubroot likely originated in Europe and spread to North America in the 1800s. It was first described scientifically in Russia in 1878 and is now present throughout the world.
Proper identification, prompt treatment, and diligent prevention enables successful management of the clubroot disease in brassica crops. With care, gardeners and farmers can continue growing healthy, productive vegetables even where clubroot is present.
Conclusion
Clubroot can be a very destructive disease for brassica vegetable crops, but plant health can be maintained with proper management. Identifying symptoms early and accurately is the first critical step. Swollen, club-shaped galls on roots confirm infection. Once detected, prompt treatment measures such as solarization, liming, fungicides, and sanitation can limit the spread. However, prevention is always more effective than treating clubroot once established. Test soils before planting, maintain optimal pH, use clean containers and tools, rotate crops, choose resistant varieties, and regularly scout for early symptoms. Combining identification, treatment, and prevention techniques empowers gardeners and farmers to successfully manage clubroot and keep their brassica crops productive. With proper knowledge and vigilance, clubroot does not have to spell disaster in the cabbage patch.