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Post Date:

24th Oct 2022

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Clubroot is a fungal disease that can severely affect brassica crops. If you have this pathogen in your soil it can have disastrous effects on your harvests but can be managed. GrowMad's David digs a little deeper...

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Clubroot in brassicas: What is it and How Do You Manage it.

| Introduction

Clubroot is a highly destructive disease that affects the roots of all members of the Brassica family.

On the allotment, this includes cabbage, cauliflower, broccoli, Brussels sprouts and to a lesser extent, kale. It can also affect swede, turnips, radish and cruciferous weeds such as shepherd's purse and charlock.

If you are interested in finding out more about this particular disease or suspect you may have it in your soil, read more.

There is a lot to cover, so let's get to the root of it...

| What is Clubroot?

Clubroot in brassicas is caused by the fungal pathogen Plasmodiophora brassicae.

Roots become infected by spores that enter root hairs where the pathogen stimulates root cell multiplication. This causes swelling of the roots manifesting itself with the characteristic 'clubby' looking galls.

This root swelling prohibits the normal uptake of water and nutrients resulting in the yellowing of foliage, poor growth and ultimately, loss of yield. In severe cases, it will result in the eventual death of the plant.

As the host plant roots decay, resting spores are released back into the soil which can remain viable for up to 20 years.

Clubroot is normally associated with acidic soils with a high clay content that suffer from poor drainage. Planting during warm weather is also highly conducive to this damaging disease.

If you are uncertain whether you have it in your soil, clubroot tests are available.

| Managing Clubroot

There are at present no chemical controls for clubroot in brassicas.

The disease can persist in the soil even without host plants being present for many years, so prevention is essential by practising good husbandry.

If you are unlucky enough to have your soil infected, there are methods and cultural practices available to minimise any potential issues:

Avoid infected soils - The obvious one. If you have signs of clubroot in your soil, try and avoid planting brassicas into infected soil.

Good plot hygiene - Hygiene on your plot or allotment is always a good idea in any circumstance but even more prudent when it comes to clubroot contamination. Always remove any brassica plant debris from the soil and avoid putting it on the compost heap. Always clean tools and footwear when moving from plot to plot.

Soil structure - Clubroot is more prevalent in soils with high clay content. Try adding more humus.

Soil pH - Soils with a pH of less than 7 will be more liable to infection than soils with a more alkaline number (7 upwards). The lower the number (more acidic) the higher the chances of the pathogen being present. Add lime to increase the pH level of your soil but never overdo it, test the pH levels first. Having a pH level that is too high will limit available nutrients in the soil.

Improve drainage - Poor drainage is a main contributing factor towards clubroot infection. Improve drainage or grow in raised beds.

Crop rotation - As with any crop, crop rotation in brassicas is a good cultural practice. Leave as many seasons as

possible between replanting brassica crops in the same soil.

Raise your own plant material - Raising your own plants in fresh compost is one way of ensuring you do not introduce clubroot into your soil. When purchasing plant material from 3rd parties, you can never be certain of what you are bringing in. Also, try growing plants in pots for longer before planting, even into 2 ltr pots.

Control brassica weeds - Ensure your soils are free of any brassica-related weeds such as shepherd's purse or charlock and any oilseed rape volunteers that may find their way onto your soil, they can act as host plants to the clubroot zoospores.

Water - Always be certain that your water is free of spores. Clubroot spores can be transferred into water supplies from runoff from contaminated land.

Boron deficiency - Boron is highly soluble and can easily be leached from the soil. Having sufficient boron levels in the soil can help reduce clubroot.

Calcium Cyanamide (Nitro Lime) - Calcium Cyanamide is manufactured and marketed as Perlka. Perlka contains 20% nitrogen and 50% calcium oxide. As well as providing a source of slow-release nitrogen and calcium, it has a biocontrol effect on the soil and acts as a mild soil sterilant. It is, however, completely soil-friendly and readily broken down by soil microbiota.

Planting dates - Planting brassicas during the cooler months of the year will assist in avoiding serious issues with clubroot.

Clubroot-resistant varieties - There are several species of brassica that have varieties bred with high levels of clubroot resistance. There will inevitably be more varieties available in the next few years. It is recommended that resistant varieties be integrated with other control measures.

You can find a comprehensive list of clubroot-resistant varieties below: