Rust is a fungal disease that robs a plant of nutrients and water. It appears as reddish spots on the underside of leaves and is the most common problem in the Bluegrass Regions humid climates. Rust is usually a late season or fall garden problem.
If rust has been a problem in your garden do not water from above. Drip irrigation will keep the roots water, but not keep the leaves wet.
Bacterial blights – common blight, halo blight and brown spot – and bacterial wilt diseases usually come from contaminated seeds. This will leave brown or tan dead areas on the leaves as spots or blotches, many times with a yellow border. Pods may also show brick-red or brown sunken blotches. Always buy fresh seeds and allow room for air to circulate around the plants. This disease also likes the high humidity of the Bluegrass Region.
The following are 3 organic recipes to help with rust and other fungal problems with your beans:
1. Potassium bicarbonate Fungicide - Mix 4 teaspoons (about 1 rounded tablespoon) of potassium bicarbonate into one gallon of water. Spray lightly on foliage of plants afflicted with black spot, powdery mildew, brown patch and other fungal diseases. Potassium bicarbonate is a good substitute for baking soda. There are commercial EPA registered as well as generic products available.
2. Baking Soda Fungicide - Mix 4 teaspoons (about 1 rounded tablespoon) of baking soda and 1 tablespoon of horticultural oil into one gallon of water. Spray lightly on foliage of plants afflicted with black spot, powdery mildew, brown patch and other fungal diseases. Avoid over-using or pouring on the soil. Potassium bicarbonate is a good substitute for baking soda. Citrus oil and molasses can be used instead of horticultural oil.
3. Vinegar Fungicide - Mix 3 tablespoons of natural apple cider vinegar in one gallon of water. Spray during the cool part of the day for black spot on roses and other fungal diseases. Adding molasses at 1 tablespoon per gallon will again help.
When you have bean leaves that have been skeletonized, you are dealing with the Mexican bean beetle. It looks so much like a lady beetle that gardeners often confuse the two at first glance, but Mexican bean beetles are coppery or bronze-colored with 8 black spots on each wing. Companion planting is an effective way to head these beetles off. Interplant your beans with dill, potatoes, sage or tansy to attract the insects’ natural predators.