Clubroot on radish — symptoms and treatment

Severity: high

What is Clubroot

Clubroot in radish is caused by Plasmodiophora brassicae, a soil-borne organism that affects all brassicas and distorts root development. In a radish that is the whole crop — the root is what you grow it for, and clubroot deforms it directly. The pathogen lives in the soil rather than on the plant and persists there for years, so clubroot is a problem attached to the ground rather than to one season's planting. Once a bed has it, it keeps it, and no spray changes that. Hence the high severity.

Symptoms

Above ground, the first thing you notice is wilting in warm weather. This is the diagnostic clue worth understanding: distorted roots cannot move enough water to keep up with demand when the sun is strong, so plants flag on hot afternoons even where the soil is moist, often recovering overnight only to wilt again the next day. Alongside this, growth is stunted and the leaves yellow. Pull a struggling plant and the cause is unmistakable — instead of a clean radish you find swollen, misshapen roots distorted into gnarled lumps.

• Early: wilting in warm weather; recovery overnight.
• Progressing: stunted growth; yellowing leaves.
• Confirmed underground: swollen, misshapen roots.
• Confusable with: drought or nutrient deficiency — the top growth looks similar, so never diagnose clubroot from the leaves alone. Lift a plant and check the root.

Causes and conditions

The pathogen survives in soil as tough resting spores that stay viable for years. They germinate near brassica roots and infect them, the root swells and distorts, and when that tissue decays it releases another generation of spores — so every infected crop leaves the bed worse than it found it. Acidic soil favours the pathogen, which is the basis for liming as the core control measure. Wet, poorly drained ground helps it too, because the infective stage moves through soil water. It spreads on anything carrying infested soil — boots, tools, wheelbarrows, run-off — and most often arrives in a clean garden in soil moved from an infested bed.

Treatment

Liming and rotation — cultural

Timing: pre-planting. Raise soil pH above 7.2 with lime. Rotate with non-brassicas for 7+ years in infested fields.

Both parts of that timing matter. Liming has to happen before planting, not in response to symptoms — soil pH does not change overnight, and a radish with distorted roots will not recover whatever you do to the soil around it. There is no spray that cures a clubbed root; everything effective happens in the ground before the crop goes in. The long rotation starves the resting spores of the brassica hosts they need, and 7+ years reflects how long they persist.

Prevention

• Test the soil and lime in advance to raise the pH above 7.2 wherever brassicas will be grown.
• Rotate with non-brassicas for 7+ years in infested ground.
• Improve drainage — the infective stage moves through soil water, so wet beds work against you.
• Clean soil off boots, tools and wheelbarrows before moving from an infested bed to a clean one, and avoid working infested ground when wet.
• Pull and destroy affected plants with the roots intact; leaving distorted roots to rot in the soil feeds the next generation of spores.

Frequently asked questions

My radishes wilt on warm days but the soil is moist — is it clubroot? It is a strong indicator. Wilting in warm weather despite moisture is the classic picture, because distorted roots cannot supply water fast enough. Confirm by lifting a plant and looking for swollen, misshapen roots.

Can I still grow other vegetables in that bed? Yes. Clubroot only affects brassicas — radish, cabbage, broccoli, cauliflower, kale, turnips and brassica weeds. Everything else grows normally, which is what makes the long rotation practical.

Does liming cure the soil? It suppresses the disease rather than eliminating it. Raising the pH above 7.2 makes conditions hostile to the pathogen and lets you grow a crop, but the resting spores persist for years — so combine it with the rotation rather than relying on lime alone.