Beans are a favorite in the veggie patch, and not only for us! Many types of bean blight exist, caused by fungus, viruses, mites and bacteria. They infect bean plants and trigger brown or yellow spots,wilt, and other issues on bean leaves, bean pods and vines.
Here are the main culprits responsible for bean blight.
Fungus, virus, bacteria and mites trigger the following seven of the many diseases bean plants can catch.
Start from what is in front of you rather than from a list of names. Each row below leads to
the section that describes it in full.
| What you see | Likely cause | Type | First move |
|---|---|---|---|
| Brown patches edged with yellow, on leaves and on pods | Common bean blight | Bacteria | Remove and destroy. Never save seed from these plants |
| Pods turning soft and mouldy, low down near the soil | Phytophthora blight | Oomycete | Lift the pods off the ground, improve drainage |
| Fine pale stippling, and webbing under the leaves | Spider mite | Mite | Spray water underneath. It thrives in dry heat |
| Round spots ringed by a wide pale halo | Halo blight | Bacteria | Destroy affected plants, then rotate for three years |
| Tan round blotches with no halo | Bacterial brown spot | Bacteria | Stop overhead watering; keep the foliage dry |
| Sudden wilt, the whole vine collapsing while still green | Bacterial wilt | Bacteria | Pull the plant out. Do not compost it |
| Yellow and green mottling, leaves puckered and distorted | Mosaic virus | Virus | Pull out and control aphids, which carry it |
Common bean blight, or common bacterial blight, is the result of infection by either of two related bacteria. One of these also infects citrus plants, so it’s more likely to appear if you’ve also got a citrus orchard nearby.
Phytophthora blight is a plant disease where bean pods turn mushy and mold away. Usually this happens when the pods form near the soil. Varieties with very long pods like string beans are more vulnerable since they occasionally reach down to the ground.
Red spider is a type of mite that feeds on sap. It drains leaf cells of their chlorophyll, turning them pale yellow. Webs appear.
Halo blight results in round spots forming on bean leaves and pods. In extreme cases, vines dry out.
Note the last word in the name to distinguish it from halo blight above: the “pathovar” descriptive is different. This is the same species of bacteria as above, but it’s a different group within the species. Interestingly, symptoms are different because the spots on the leaves don’t look the same. For instance, the color of this infection is a deep brown, hence its other common name: chocolate spot of bean.
The bacteria causing this disease also infects other host plants. Initially, brown spots form that seem swollen with water. As it spreads in the plant, it eventually reaches the root system. It causes the roots to rot, to the point they can’t channel water to the vine and stem anymore. In a few days, leaves show signs of chlorosis, the plant wilts, dries up and dies from tip to root.
Another group from this same species, Curtobacterium flaccumfaciens pv. oortii, infects tulip bulbs. It causes bacterial canker in tulip (yellow pustule).
Viruses are the cause of dreaded mosaic bean blight. Leaves take on a patchy appearance, portions turning yellow while the rest remains unscathed. These viruses don’t get there on their own: host pests inject them into the plant.
Two columns decide what you do next: the dormancy, which sets how long the ground and the
seed stay contaminated, and the host range, which tells you what else in the plot is at risk.
| Disease | Culprit | Type | Dormancy | Main hosts |
|---|---|---|---|---|
| Common bean blight | Xanthomonas phaseoli pv. phaseoli, X. fuscans, X. citri pv. fuscans | Bacteria | Indefinite — over 15 years inside bean seed | Bean, lupin, pea |
| Phytophthora blight | Phytophthora capsici, P. phaseoli | Oomycete | Indefinite while the soil stays moist | Cucurbits and peppers chiefly; bean, tomato, aubergine are minor hosts |
| Spider mite | Tetranychidae | Mite | Overwinters as adults in debris | Almost anything, in dry heat |
| Halo blight | Pseudomonas syringae pv. phaseolicola | Bacteria | 2 years, or until the plant debris has fully rotted | Bean, all species |
| Bacterial brown spot | Pseudomonas syringae pv. syringae | Bacteria | 2 to 3 years in infected material, then dwindling | Lilac, all Prunus (cherry, plum), and all beans |
| Bacterial wilt | Curtobacterium flaccumfaciens pv. flaccumfaciens | Bacteria | Indefinite — over 24 years in dried beans | Bean, all families |
| Mosaic virus | Sobemoviruses | Virus | Undetermined in soil; carried by aphids | Bean and many others, tobacco included |
The two indefinite entries are the reason seed is never saved from an affected row. Fifteen
years for common blight, twenty-four for bacterial wilt: no rotation outlasts that, because the
pathogen is not in the ground, it is in the bean.
The first and most effective manner to avoid having to deal with these diseases every year is crop rotation. Most of these pathogens only stay for 2 or 3 years in high amounts in the soil. This means that you should practice a 4-year crop rotation plan. By the time beans grow on the same plot of soil again, levels of bacteria will have dropped to very low levels. They won’t be able to devastate your crops entirely.
However, it’s nearly impossible to eradicate them completely just by rotating the plants over 4 years. There will always be a few bacteria that will reappear. Nonetheless, they won’t be numerous enough to cause any real damage.
Crop rotation is, by far, the most natural solution to prevent bean leaf blight: no additives and no extra work! All you have to do is avoid planting beans in the same spot, and infection drops to acceptable levels.
These bacteria and oomycete spread thanks to water. Keeping leaves dry is an excellent way to help protect the plants.
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Thank you- Great information- Address treatment for diseases