Help us achieve our goals:
make a donation »
Join the RHS today and
support our charity
Free personalised gardening advice
RHS members get reduced ticket prices
RHS members get free access to RHS Gardens
Reduced prices on RHS Garden courses and workshops
020 3176 5800
Mon – Fri | 9am – 5pm
Make a donation
Join the RHS today and support our charity
Register for free to receive our newsletters, add comments to blogs/articles and to save content.
Chocolate spot is one of the most common fungal diseases of broad beans. The fungus causes dark, chocolate-coloured spots on all parts of the plant.
Chocolate spot is caused by two species of the fungus Botrytis. Botrytis fabae is the most common cause and only affects broad beans. Botrytis cinerea can cause very similar symptoms, and this fungus also causes grey mould on a very wide range of plants. Chocolate spot can be very damaging, in some cases causing flower loss, with severe attacks resulting in whole plant collapse. It is worse in cool, damp, overcrowded conditions. This disease appears from late winter on autmn sown crops, but is seen from mid-spring on spring-sown broad beans.
No other beans including runner and French beans are affected, although common vetch and agricultural field beans sometimes used as green manures can be infected.
You may see the following symptoms:
There are no fungicides available to amateur gardeners for the control of broad bean chocolate spot.
The fungus produces masses of air-borne dispersal spores under wet conditions which spread the disease. It may also produce overwintering seed-like resting structures (sclerotia) in dead tissues, but their role in the disease cycle is unclear. The disease can be transmitted on infected seed. It also infects common vetch and these infections may also carry the fungus over the winter months, as can lesions on autumn-sown broad beans.
Under dry conditions the pathogen remains contained within the small round spots, but under wet conditions it spreads outwards and the lesion expands rapidly. Alternating wet and dry weather may lead to a spot with a series of concentric growth rings, but in longer periods of wet weather the leaf is rapidly killed.
Another fungal pathogen, Didymella fabae (syn. Ascochyta fabae), causes spots on leaves and pods, but is usually less damaging than chocolate spot.
Broad bean rustBroad bean seed beetleBroad beans: growingDisposing of diseased materialGrey mouldRunner and French bean rustRunner beans
the RHS today and get 12 months for the price of 9
RHS members can get exclusive individual advice from the RHS Gardening Advice team.
Register for the site or sign in to share your experiences on this topic and seek advice from our community of gardeners.
Verity Coleman on 28/03/2015
If the leaves are affected by this disease/ rust, will removing the infected leaves save the plant?
We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.
Like this page on facebook
Click on the Tweet button below to compose your tweet.
Join the RHS today and get 12 months for the price of 9