Brown spots on beans and leaves of the bean plant almost always indicate burn spot disease. This is a very aggressive fungal infection. Below you will find out how to act correctly in the event of an infestation.
The bean plants should be removed promptly before the fungal pathogen spreads
Which beans are affected?
The burn spot disease mainly affects bush beans and is rarely found in pole beans. As with all diseases, weakened plants are particularly affected. These circumstances favor the disease:
- wrong location, for example too dark
- wrong watering (too much or too little water)
- nutrient deficiency
- already infected seeds
Identify burn spot disease
Brown spots on the bean are usually an unmistakable sign of focal spot disease. However, to be on the safe side that your beans really do have focal spot disease (Colletotrichum lindemuthianum), take a close look at the brown spots. How to recognize the fungal infection:
- the spots emanate from the leaf veins, but are also found on the pods and stems
- the spots are only half a centimeter to one centimeter in size at the beginning
- the spots are brownish to reddish and have a dark colored border
- they are often plump and self-contained
- the parts of the plant have sunken at the affected area
How do you react correctly?
Burn spot disease cannot be treated. Therefore, in the event of an infestation, there is only one thing left to do: remove all infested plants immediately and dispose of them in the residual waste, never in the compost! You should never sow seeds from infected plants, as there is a high probability that they are also infected and the disease would break out again.
The fungus is extremely resistant and can survive in the soil for up to two years. So be sure to plant a resistant strain next year. However, the pathogen does not like intense heat, which is why treatment with hot water over 50° is possible. However, you should bear in mind that you will harm small animals and microorganisms in the soil.
It therefore makes more sense to lay out a film before removing the infested beans to ensure that no plant remains fall on the ground and thus completely banish the pathogen from your garden bed.
tips
Focal blotch also affects peas. So also check your pea plants for infestation and do not sow any peas in the affected area next year.