Broad Bean Pests And Diseases

In general broad beans are a simple vegetable to grow however like everything in the garden they are prone to certain pests and diseases.

One of the most common problems that we and many others have experienced is the formation of black spots forming all over the broad beans stems. In actually fact you will find upon closer examination that these black spots are actually tiny clusters of black flys, otherwise known as black aphids. These aphids produce honeydew as they attack the plant, which in turn attracts ants to the plants, and this can lead to the common misconception that the black spots are any eggs, whereas in reality the ants are eating the black fly aphids and the honeydew.

Whilst a pest the ants are not actually harming the plant, however the black fly are as they are drinking the plants sap, and if unchecked this can cause the plant to lose nutrients and stunt the broad beans growth.

The ants can be removed by a good solid spray of water, but they may well come back.

The black flys can be tempted away from the broad beans by growing nasturtiums nearby, which aphids just love, or you can spray the beans with a diluted solution of washing up liquid. Just note not to make it too strong, and we have found that it will need doing quite often. Ideally do it whilst the broad bean plants are young before the black fly problem appears, as prevention is far easier than cure.

Another problem is the common weevil which can attack broad beans, if they are young plants the adult weevils and their young larvae can eat through the plants roots causing major damage.

Another common problem is chocolate spot, which takes the form of red/brown blotches that can spread rapidly if untreated across the leaves. It is actually a form of grey mould, and if unchecked it will affect the flowers and discolour the contents of the seedpods, ruining them.

In general chocolate spot is spread by consistently damp conditions on the broad beans, so the key to avoiding it is to plant them in well drained soil, and leave 50cm between the rows of plants to ensure good airflow around them. Raised beds are a good idea to help with drainage. Of note is for this broad bean disease there is no chemical solution available to prevent it.

Lastly we come to broad bean rust, which results in the beans leaves being covered in small yellow spots, which then turn red/brown. This can affect the leaves, stems and pods. The good news is that most times if affects the plants only late on and so does not affect the broad bean yield, however it can affect late sown broad beans. It cannot be stopped with any chemical spray, however it can be slowed down by picking off the effected broad bean leaves.

By Richard Allen -

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