Bush beans

Asked July 9, 2018, 11:53 AM EDT

I have a raised bed vegetable garden with brand new very expensive garden soil. I believe I may be watering too much but everything is doing fine except my green beans with leaves are really yellow and I don’t understand what I’m doing wrong. I have read that magnesium could be the answer. The rest of the garden seems to be doing fine

Clackamas County Oregon vegetables horticulture

1 Response

Thank you for contacting Ask an Expert in regards to your Bush Beans.

There are a host of possibilities for the yellowing of the leaves on your bush bean crop. I will start with some basics that might be the cause: If your weather has been poor lately, your beans are probably chlorotic (yellowed) as a result. Hopefully, when sun & warmth return, they will recover. Even if your weather has been good, legumes in general often go through a period of yellowing shortly after germination. The seeds have exhausted their stored nutrients, and the root system has not yet begun to supply adequate nitrogen. This situation is only temporary, and the plants usually green up in a week or two on their own... under ideal conditions. A single, light application of N (whether chemical or organic) at the time of planting will minimize the yellowing, and might be advisable for cooler climates, where bean growth tends to be slower.

Sun and Water

Pole beans need at least eight hours of sun daily. If they don't get enough sun, the leaves may yellow because they can't produce as much chlorophyll. Lack of sunlight can also keep water from drying on the leaves after a rain, which can lead to fungal diseases. It is important to give the beans enough water to keep the soil moist but not flooded. Overwatering can rot roots. The leaves will yellow as a result of non-functioning roots. Remove dirt over the roots to check root health.

Nutrient Deficiencies

Proper fertilization promotes bean plant health. The best way to make sure the plants are getting enough nutrients is to have the soil tested before planting and add necessary fertilizers based on the results. A nitrogen deficiency causes leaves and plants to be light green or yellow. The vine may also suffer from slow, inadequate growth and produce few flowers. A manganese deficiency causes older leaves to turn yellow and develop dead brown spots.

Disease

Mosaic disease affects beans by producing mottled yellow patches on leaves and yellowing of plants. Planting mosaic-resistant varieties is the only solution for the virus. Bacterial blight causes spreading yellow spots on leaves. Keeping leaves dry can help prevent fungal diseases. Bean rust symptoms include yellow leaves with brown dust on the undersides. Rust infects plants in cooler weather. Multiple applications of sulfur spray can control the fungus and should begin when rust first appears.

Insects

Root-knot nematodes, microscopic parasitic worms, infest the roots of the beans and prevent them from absorbing nutrients. The leaves yellow and the plant's growth is stunted. Soil solarization when the soil is cleared kills nematodes. Thrips suck sap from plants, making the leaves yellow and distort. Look under leaves for small tan or black insects and remove infected foliage. Yellowed leaves with sticky honeydew on the leaves indicates whiteflies. Shake the plant and the insects will fly out. Remove infested foliage.
Try a resistant seed strain, practice crop rotation and careful cultivation
Soil must be well drained, in full sun and tilled with plenty of compost mixed into the site. Alkali soil can cause iron chlorosis. However, adding chelated iron or soil acidifier helps if the plants develop yellow leaves from alkali soil. Beans have shallow roots, so exercise care when hoeing to prevent injuring the roots. Remove any old plant debris from the area as these may host disease organisms. To ensure that soils are not transferring diseases to the beans, practice crop rotation annually. If you still have yellow leaves on beans, the cause is likely disease. Yellow leaves on bean plants in the garden may have several causes, though the most common are usually due to mosaic virus or blight.

Bacteria

When a bacterium is to blame for yellow leaves on beans, the first sign of a problem is water spotting or dry, brown leaf edges. This progresses to encompass the entire leaf and causes the foliage to die and drop off. Foliar loss diminishes the plant’s ability to gather solar energy and minimizes the health of the beans. Yellow leaves on bean plants might be from blight. Halo blight is a disease that causes round yellow spots, which slowly blend to turn the entire leaf yellow. The bacteria that cause this disease live in soil or are introduced in infected seed. Choose a seed that is resistant to the blight and rotate your bean crop.

Virus and Yellow Leaves on Beans

Garden beans with yellow leaves can also be the result of a viral infection. Mosaic virus may affect many different types of vegetables, and there are several bean mosaic viruses, which appear in different regions of the country. The initial symptoms are multi-colored spots on the leaves, which give way to an entirely yellow to brown leaf. If bush or pole beans have yellow leaves, the problem might be a virus. Unfortunately, there is no cure. Virus problems may be develop from low nutrient levels or even herbicide injury but is most likely from infected bean seeds. Do not save seeds from year to year, as they may harbor the virus. Some viruses are also transmitted from sucking insects, such as aphids. Practice good pest control and use a mosaic resistant bean seed to reduce the chance of yellow leaves on beans. Hope your bean harvest is successful.

Reference: http://homeguides.sfgate.com/leaves-turning-yellow-pole-beans-49779.html