Picture courtesy of: Howard F. Schwartz,
Colorado State University, Bugwood.org
Runner Bean Diseases
Halo Blight
This is a seed-borne disease.
It takes the form of small brownish spots on the leaves that are surrounded by a light coloured 'halo', the spots may also be yellowish in colour and the spots are generally transparent.
This disease comes from the seeds themselves. Possible causes are:
Home-saved seeds from the previous years:
Which had not been completely dry when stored.
Or the seeds became damp whilst in storage;
soaking runner bean seeds before planting;
seeds bought from a bad source.
It's a good idea to examine the seeds at planting time and reject any which are; marked, wrinkled, or misshaped.
There is no cure, dig up and destroy the plants.
If Halo blight spotted early you might be able to save the plant by removing infected leaves. At the end of the season ensure that you destroy the plant do not put it on the compost heap. Also do not keep any seed from that plant.
Bean Anthracnose
This is another seed-borne fungal disease. The culprit is Colletotrichum lindemuthianum which thrives in damp wet conditions.
This is sometimes called ‘blight’, ‘Rust’ or ‘Canker’. It is more likely that these names refer to other diseases having similar symptoms. But caused by other bacteria or fungi.
The symptoms are black spots that grow into circular sunken pits. These pits have red lines surrounding them.
Any part of the plant can become infected. The best control against this disease is to have clean seed and crop rotation.
It might be possible to control the disease by spraying with a dilute Bordeaux mixture. But never spray once the plant is in flower.
Botrytis
This is a very common fungal disease caused by Botrytis cinerea and goes by the popular name grey mould. The name grey mould comes from the appearance of fluffy grey mould on infected plants. It affects many plants and is always present in the atmosphere.
Botrytis fungus thrives in cold, wet weather conditions. And still air encourages its growth.
For runner beans, it is the seedlings that are most at risk, especially if they have been started off in a greenhouse or cold frame.
This disease lives on dead or decaying plant material. It infects living plants through wounds. These can be either mechanical i.e. broken leaves or dying leaves caused by another disease.
The use of fungicides to reduce primary damage will help to prevent the spread of botrytis. Due to there being fewer dead leaves for it to enter by.
In the UK they are no fungicides available to home gardeners for specific control of grey mould.
Root Rot
This occurs when the weather is cold and the soil does not drain well. This combination weakens the roots making them vulnerable to soil-borne fungi. The only method to prevent this is to ensure good drainage
Bean Mosaic
This is a viral disease and is sometimes called "streak", leaf roll, or yellow edge.
The symptoms are yellowish-green areas against the darker green of the infected leaf.
As there are no chemical controls for plant viruses the best course of action is prevention. i.e. use seed that is from a reputable source, keep the area weed-free as many weeds can harbour plant viruses.
Use whichever method you prefer to control aphids and other sucking insects.
After handling infected plants clean your hands and tools with a good disinfectant. Do this before carrying on with any other work in the garden.
Runner Bean Pests
Blackfly
This is an aphid that smothers the growing points of the runner beans in late spring.
Natural predators are ladybirds and hoverflies. To encourage these plant Marigolds near too the runner bean plants.
You can also knock the blackfly off the plants by spraying with water. If these methods do not work, then it’s time for a chemical solution, most work well.
Greenfly
This is another aphid but green in colour. It mostly affects the underside of the leaves making them hard to see.
Treatment is the same as blackfly
Slugs
Slugs find all parts of runner beans delicious - the roots, stems, leaves and of course the pods.
Slugs feed after dark, both above and below ground. Their favourite hiding places during the day are cool, dark and moist. Generally in decaying vegetable matter and heavy moist soils.
Slugs have a great defence against chemicals by excreting slime. Which is why any chemical control needs a nightly application. Whenever using chemical controls always follow the manufacturer's instructions.
There are two non chemical controls that work well for runner beans. 1 sprinkle dry multi-purpose compost around the plants. 2 Cut the bottoms of large plastic soft drinks bottles and place over the young plants.
1 Multi-purpose compost
With this idea, we will be using the fact that the young runner bean plants will be growing in early summer. While not guaranteed this time of year is usually dry which gives us an advantage.
By sprinkling a layer of dry, fine multi-purpose compost covering 15cm (6 inches) of soil around each plant. Slugs dislike crawling over this as it is uncomfortable for them. If the compost becomes wet replace it with new dry compost.
2 Plastic Bottles
Cut the bottoms of large plastic bottles and place them over the young runner bean plants. This creates a physical barrier for the slugs to overcome.
One problem with this is on a hot day these will act as a mini-greenhouse and scorch the plants. So on days when it will be hot remove the plastic. The slugs will be hiding from the heat so no damage will occur. Remember to replace them that night!
Snails
These are very like slugs with the exception they only feed above ground. Hence the same treatment applies.