Chocolate Spot
Botrytis fabae
A fungal leaf disease of fava and broad beans that peppers the foliage with reddish-brown spots, and in wet, crowded conditions blackens whole plants and slashes the crop. It is the most damaging disease of fava beans in cool to mild, humid climates and flares around flowering.
🔎 How to spot it
The early sign is many small, round, reddish-brown to chocolate-colored spots scattered over the leaves, each often with a slightly paler grayish center and a darker margin. In the mild aggressive phase these spots stay small and discrete, but under wet, humid conditions they merge into large gray to black blotches that spread to stems, flowers, and pods, and the leaves blacken, wither, and drop. Flowers may blacken and fail to set pods.
🥀 Damage it causes
Light spotting mainly blemishes the leaves, but in the aggressive phase the disease kills large areas of leaf, stem, flower, and pod tissue, so plants are defoliated, flowers abort, and yield falls sharply. Severe outbreaks at flowering can blacken and collapse much of the planting. Pod and seed infection lowers quality and can carry the fungus into next year seed.
🔬 What causes it
Chocolate spot is caused by the fungus Botrytis fabae, with Botrytis cinerea sometimes contributing, surviving on crop debris and seed and spreading by airborne and splashed spores. It is most aggressive in humid, wet conditions with mild temperatures, especially in dense, lush, over-fertilized stands around flowering, and is worsened by anything that keeps the foliage wet and the canopy from drying.
🛡️ Prevent it
Sow at the proper spacing and avoid overly dense, lush growth so air moves through and the canopy dries quickly, and orient rows to the prevailing wind where possible. Use clean, certified seed and resistant or tolerant varieties, rotate fava beans onto fresh ground on a multi-year cycle, and remove and destroy old bean debris after harvest. Avoid excess nitrogen, and ensure good potassium and phosphate nutrition, which lessens severity.
🧯 If it is already here
Where the disease is established and weather turns cool and wet around flowering, a protectant foliar fungicide applied before rain and repeated as needed gives good control, even on susceptible varieties. Cultural steps remain the foundation: improve airflow, remove infected debris, and rotate. Pick off and destroy the first spotted leaves in a small planting to slow the buildup.
💡 Good to know
Chocolate spot has two faces: a harmless-looking scatter of brown spots that can explode into a plant-killing black phase once the weather turns wet at flowering, which is the moment to act. Crowded, over-fertilized, poorly drained plantings are the classic setup for a severe outbreak. Clean seed, spacing, rotation, and debris cleanup prevent most trouble.
🌱 Plants it affects
9 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.