Cavity Spot
Pythium violae and related species
A soilborne disease of carrots, caused by water-mold fungi, that pits the roots with small sunken lesions and makes them unsellable. The spots usually appear as the crop nears maturity and are worst in cool, wet, poorly drained soil, so a fine-looking carrot crop can be marred just before harvest.
🔎 How to spot it
Look for small, sunken, oval lesions running crosswise around the carrot root, at first just a fraction of an inch long with a pale, slightly elastic surface, later darkening and enlarging into pits up to about a quarter inch or more. The spots stay shallow and usually do not lead to deep secondary rotting, but numerous pits make the roots rough and unmarketable. The tops generally look healthy, so the damage is found only when carrots are pulled.
🥀 Damage it causes
The pitting itself is mostly cosmetic in that it does not rot the whole root, but even a few lesions per carrot render the crop unsellable and reduce quality and storage life. Damaged carrots are also more prone to other rots in storage. Losses can be heavy in a wet year on land with a history of the disease.
🔬 What causes it
Cavity spot is caused by several species of Pythium, water molds that live in the soil and infect carrot roots, with Pythium violae and Pythium sulcatum among the most damaging. They are favored by cool, wet, poorly drained soils and by long periods of saturation, and the risk rises the longer mature carrots sit in moist ground.
🛡️ Prevent it
Grow carrots on well-drained ground or raised beds and avoid fields with a known history of cavity spot, since the pathogens persist in soil. Do not over-irrigate, keep soil moisture even rather than swinging between dry and saturated, and rotate carrots with non-host crops to keep populations down. Harvest on time, because carrots left in cool, wet soil past maturity develop far more lesions.
🧯 If it is already here
There is no rescue for already-pitted roots, so control is preventive: improve drainage, manage irrigation, rotate, and harvest promptly before lesions multiply. Choose more tolerant varieties where the disease is chronic. On problem ground, soil-applied fungicides labeled for cavity spot can reduce it, but cultural management of moisture and harvest timing is the foundation.
💡 Good to know
Cavity spot is easy to confuse with feeding injury or other root spots, but the shallow, crosswise sunken pits on otherwise firm carrots with healthy tops are characteristic. Because the disease worsens the longer mature carrots stay in wet soil, simply harvesting on time is one of the most effective controls. Wet, heavy, poorly drained ground is the classic setup for trouble.
🌱 Plants it affects
11 plants in the library can be affected by this problem
For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.