Divisi
Cavity spot
Pythium violae · Fungal
Photo: Hellerhoff · CC BY-SA 4.0
Cavity spot is a soil-borne disease of carrots and parsnips caused by a soil fungus (Pythium violae and its relatives) that lives in the ground and attacks the root as it swells underground. It eats small, sunken oval pits into the root's skin. The damage is only skin-deep, but because these roots are sold on their looks, the pits downgrade or reject them for the fresh market. It thrives in wet, poorly drained, cool soils and in long crops and short rotations — and once the pits show, there is no cure.
Hellerhoff · CC BY-SA 4.0 
Frans Segerink · CC BY-SA 4.0
Why it matters
Cavity spot doesn't wilt the leaves or shrink your tonnage — it eats small sunken pits into the skin of the carrot or parsnip while the root grows underground, out of sight. Carrots and parsnips sell on their looks, so even a few pits push a root from fresh-market grade down to processing or the reject pile, and in a bad wet year up to 6 in every 10 roots (60%) can be lost this way. The worst part: the fungus hides in the soil and infects the root as it swells, so by the time you see the pits at harvest it is too late to spray — there is no cure. This disease is won or lost before you plant — in the field you pick and the way you drain it.
When to act
A quality (not spray-timed) threshold: lesions found on lifted sample roots mean the crop must be marketed or graded accordingly; there is no rescue spray once symptoms show.
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full cavity spot field guide
- Identify it
- Scout for it
- Control it
18 field-guide sections in the app
The full guide to cavity spot — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify cavity spot?
The main sign — sunken pits on the root: you only see it when you pull a root, because all the trouble is below ground (nothing shows on the leaves). Look on the skin of the carrot or parsnip for small, sunken oval pits, from the size of a pinhead up to about 1 cm — the width of your smallest fingernail — usually running crossways around the root.
When should I take action against cavity spot?
A quality (not spray-timed) threshold: lesions found on lifted sample roots mean the crop must be marketed or graded accordingly; there is no rescue spray once symptoms show.
How do I control cavity spot?
Prevent it — this is where the disease is beaten, not in the sprayer. Choose well-drained fields and avoid low, wet, heavy or compacted ground. Where water sits, break up hard pans and improve drainage before you sow. Cavity spot needs wet soil; take the water away and you take away the disease.
Which crops does cavity spot affect?
Among the crops covered here: Carrot.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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