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By: Amy Grant
Under ideal conditions, beans are an easy, prolific crop for the home gardener. Advanced cases can decimate a crop. Are there any bacterial wilt treatments or, at the very least, is there any method for control of bacterial wilt? Let’s find out more.
Bacterial Wilt in Beans
Bacterial wilt of dry beans is caused by Curtobacterium flaccumfaciens pv. Flaccumfaciens. Both bacterial wilt and bacterial blight in bean plants are fostered by moderate to warm temps, moisture, and plant wounds both during and post-flowering.
The bacterium affects many types of beans including:
- Hyacinth beans
- Runner beans
- Adzuki beans
- Mung beans
The first symptoms of bacterial wilt in beans appear in the leaves. Hot, dry weather is often enough to trigger an explosion in the growth of the bacteria. It infects the vascular system of the beans, impeding water movement. Young seedlings wilt as well as the leaves of older plants. Irregular lesions also appear on the leaves and eventually drop off.
Pods may also have evidence of infection and seeds may become discolored. Infection during the initial growth phase can stunt or kill seedlings.
The bacterium survives in infected debris and is also seed borne, making it difficult to treat. So how can you control bacterial wilt?
Bacterial Wilt Treatment
This particular pathogen is a tough cookie. It can overwinter in infected bean debris and even on the debris of other crops that have been rotated in following a bean crop. The bacterium can still be viable after two years. It is spread from the debris by wind, rain, and irrigation water.
This bacterial pathogen can be managed, but not eliminated, through crop rotation, sanitation, sowing only treated certified seeds, varietal selection, and avoiding stress and excessive moisture on foliage.
- Rotate crops for three to four years with a bean crop in the third or fourth year only; plant corn, veggies, or small grain crops during the rotation period.
- Practice sanitation of not only bean debris, but removal of any volunteer beans and incorporation of straw into the soil.
- Sanitize tools and storage containers that may have been associated with the beans, as they may also harbor the pathogen.
- Only plant certified seeds. This will lessen the possibility of infection, although the pathogen can still be imported from an external source.
- Plant resistant varieties. Heirlooms and other older bean varieties, like pinto or red kidney, are susceptible to the disease. There are newer varieties currently available that are more resistant to bacterial infections.
- Don’t work among the beans when they are wet. Also, avoid irrigation via sprinklers which can spread the disease.
A copper based bactericide may reduce infection of bacterial blight and bacterial wilt in bean plants but it will not eradicate it. Apply the copper spray in the early growing season, every seven to ten days to reduce the number of pathogens.
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Leaf Wilt on Green Bean Plants
Beans are versatile vegetables. There are dozens if not hundreds of varieties. They grow on bushes or as climbing vines. Beans are relatively easy to grow. In spite of this fact, green beans are susceptible to a number of diseases and insects that can cause a great deal of damage. Green beans can also react badly if not given the proper basic care. Wilting leaves can be a sign of any of these conditions and should not be ignored.
- Beans are versatile vegetables.
- Green beans can also react badly if not given the proper basic care.
The most common bean diseases are: Anthracnose, bacterial blights, common bean mosaic, and rust.
Anthracnose is caused by a fungus, which is carried in seeds and lives in the soil on the remains of diseased plants. Rotating crops is important for control. You can recognize the disease by the brown, sunken spots that develop on the pods.
Bacterial blights cause large, brown spots on the leaves and water-soaked spots on the pods. The disease spreads quickly on wet foliage.
Common bean mosaic is caused by a virus carried in the seed and spread by aphids. Leaves become mottled and then curl. Some bean varieties are resistant to this disease.
Rust shows as red or black blisters on the leaves, which turn yellow and drop. The problem is caused by a fungus that lives through the winter on the remains of diseased plants.
When anthracnose, blights or other bean diseases hit, there isn't too much you can do except to pull up and destroy seriously affected plants to prevent the disease from spreading to nearby plants. A few sprays are recommended to fight diseases. Contact your extension service agent for more information before using them. Extension agents are usually aware of which diseases have developed in an area and what the best controls are.
Disease Prevention Steps
Here's a quick review of the basic steps to preventing disease problems in your garden:
- Stay out of the garden when plants are wet, because water is often the carrier of diseases.
- Rotate the bean crop each year to avoid soilborne diseases.
- Select disease-resistant seed varieties, and buy seed from a reputable company. You can use seed protectant on beans, too.
- Well-drained soil is important for growing beans.
- If the soil stays wet, raised beds are your best bet for beans. With raised beds the soil will be warmer at planting time, and the seedbed will drain better. Raised beds are also good for heavy soil because it won't pack down as much.
- Use mulch in the walkways and wide-row growing to prevent raindrops from splashing soil and disease spores up onto the plants.
Common blight and halo blight are bacterial diseases that causes leaves to drop prematurely. Common blight is more common in warm weather, while halo blight occurs in rainy, cool weather. Blight can live in the soil for years, sheltered in plant debris. In moist conditions, the disease can spring forth and infect otherwise healthy seeds. If you notice blight one season, buy new seeds the following season and plant them in a different area. Copper sprays may help control the disease if applied at regular intervals.
Nematodes in the soil are best controlled using a combination of practices to reduce the nematode population to numbers that do not damage the plants significantly. Gardeners using one or more of these practices can reduce the number of nematodes in the soil:
- Plant nematode-resistant varieties of vegetables.
- Rotate susceptible varieties with plants that are not nematode hosts.
- During the summer after the plants have been removed, till the soil to remove soil moisture.
- Cover the soil with clear plastic and leave it in place for 6 to 8 weeks during June, July, August, or September.
- Plant Elbon rye during the fall and early winter.
You can almost never completely eliminate nematodes. This means that each year you will need to take steps to control this pest.
No crop care chemicals are recommended to control nematodes in the home garden.
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Many bacterial, fungal and viral diseases attack vegetable crops in Maryland home gardens. Most of these are not serious and in very few cases is spraying a fungicide recommended. Foliar diseases are frequently weather dependent and vary in severity from season to season according to rainfall and temperature. Regular plant inspection, especially on lower and inner leaves, will alert gardeners to foliar problems. Foliar diseases are progressive- they begin as small spots on a few leaves. Lesions grow and coalesce and may cause leaves to yellow and die. Identify problems early on to determine the cause of the problem. Monitor affected plants through the season.
Controlling Cucumber Bacterial Wilt
The best way to prevent bacterial wilt is to keep your plants healthy. Cucumber beetles prefer feeding on wilted plants, and wilted plants are already more prone to infection. Make sure your plants are well watered and well cared for. The bacteria need a wound, such as from a deep beetle bite or a tear, to enter through, so be careful not to damage your cucumber plants. Other tips for controlling bacterial wilt include:
- Choose resistant varieties: Many cucumber varieties relatively tolerant of the bacteria spread by cucumber beetles are available on the market. Check seed packets or ask your nursery specialist to find out the best ones for your area.
- Monitor early: Keeping cucumber beetles out of your garden is the best form of control. The beetles show up in early spring and lay their eggs on the undersides of the leaves. Keep an eye out for signs of the beetles, as soon as your cucumbers are planted. Monitor the leaves and destroy any egg sacks by removing or squashing them.
- Apply barriers: You can protect early cucumber plantings by covering the plants with a floating row cover or cheesecloth. Secure the bottom of the cover so that beetles won't crawl underneath. Remember to remove the cover when the flowers appear to give pollinators access to the blooms.
- Consider pesticides: Cucumbers are very sensitive to pesticides, so use them as a last resort and follow the label directions carefully. Striped cucumber beetles are most active from dusk to dawn spraying in the evening is most effective. Use sprays containing pyrethrins since this a plant based deterrent and more organically sound. Adult beetles have a hard carapace, so you will have greater success if you spray these pests during their larval stage when they are still somewhat soft bodied.
Unfortunately, if your vines become infected, they will need to be pulled and removed. There's no cure for bacterial wilt. Remove all the vines in the fall.