Picture courtesy of: Howard F. Schwartz,
Colorado State University, Bugwood.org
Runner Bean Diseases
This is a seed-borne disease. It takes the form of small brownish spots on the leaves are surrounded by a light coloured 'halo', may also be yellowish in colour and the spots are generally transparent. This disease comes from the seeds themselves. Possible causes are home-saved seed from the previous year not stored correctly; 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 unusually shaped. There is no cure, dig up and destroy the plants. If Halo blight is caught soon enough you maybe able to save the plant by removing infected leaves, however at the end of the season ensure that the plant is destroyed and not composted and that no seed is saved from that plant.
This is another seed-borne and is caused by the fungus Colletotrichum lindemuthianum it thrives in damp wet conditions. Other names for this disease are ‘blight’, ‘Rust’ or ‘Canker’, although these names probably refer to diseases caused by different bacteria or fungi but have similar symptoms. The symptoms are black spots which grown into circular, sunken pits which are surrounded by red lines. Any part of the plant may be affected. The best control against this disease is to have clean seed and for crop rotation. A preventative spraying of half strength Bordeaux mixture may help control the disease, but the spraying must stop as soon as the beans start to flower.
Botrytis is a fungal disease caused by the fungus Botrytis cinerea and is commonly called grey mould. Botrytis is a very common fungal disease that affects many plants and is always present in the atmosphere; it appears on plants as fluffy grey mould. Usually botrytis fungus thrives in cold wet weather conditions and is encouraged by still air. Generally speaking in the case of runner beans it is the seedlings that are most at risk especially if started off in a greenhouse or cold frame. This disease lives on dead or decaying plant material and will infect living plants through entering wounds; these wounds can be either mechanical i.e. broken leaves or dying leaves caused by another disease. Currently in the UK they are no fungicides available to home gardeners for specific control of grey mould, although use of other fungicides to reduce primary damage will help to prevent the spread of botrytis as there will be fewer dead leaves for it to enter by.
This occurs mainly in cold conditions and on soil that is badly drained, this combination will weaken the roots and make them vulnerable to soil-borne fungi. The only method to prevent this is to ensure good drainage.
This is a viral disease and is sometimes called streak, leaf roll, or yellow edge. The symptoms are yellowish-green areas showing amongst the darker green area of the infected leaf. There are no chemical controls for plant viruses so the best cause of action is prevention, i.e. use seed that is from a reputable source, keep the area weed free as a number of weeds can harbour plant viruses. And use which ever method you prefer to control aphids and other sucking insects. Also after handling infected plants clean your hands a tools with a good disinfectant, before you carry on with any other work in the garden.
Runner Bean Pests
This is an aphid that smothers the growing points of the runner beans in late spring. Natural predators are ladybirds and hoverflies these can be encouraged by planting Marigolds in close proximity to the runner bean plants. You can also just knock the blackfy off the plants by spraying with water. If these methods do not work, then it’s time for a chemical solution, most work well.
Slugs find all parts of runner beans delicious - the roots, stems, leaves and of course the pods. Slugs feed mainly after dark, both above and below ground. Their favourite hiding places during the day are cool, dark and moist, mainly in decaying vegetable matter, and in heavy moist soils. Slugs have a great defence against poisons and chemicals by excreting slime, so it is important to repeat any application on a nightly basis, following the instructions given by the manufacturer.