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Common Garden Diseases and How to Identify and Treat Them

Updated on May 2, 2012
Down and powdery mildew on a grape leaf
Down and powdery mildew on a grape leaf

There are several diseases that are common for gardeners. Some are brought in by pests, some are due to environmental issues. Knowing what you're dealing with is the only way to be able to treat, or even prevent these issues.

Powdery mildew is a common fungus found in a range of plants from fruits, flowers, vegetables and trees. It is caused by several different types of fungus that are more plant specific, although they produce the same results. It is easily identified by its powdery white spots that usually form on lower level- older leaves first. It can, however, spread to newer foliage and stems. Left untreated, it can kill off entire sections of your plant, if not the entire plant. It can be treated with many fungicides that are available everywhere. Some ways of preventing the fungus are allowing more space between plants, and using lower levels of nitrogen in your fertilizers. Because it is caused by a fungus that likes moderate temperatures and high humidity, keeping plants spaced properly and making sure there is air movement around your plants makes powdery mildew less of a possibility.

Downy mildew is a fungus common in vining plants. It is similar to powdery mildew, but the spots are more of a yellowish green color than the white coloration of powdery mildew. Fungicides are very effective in reducing the affects of downy mildew.

Tobacco mosaic virus is another commonly found disease in plants. While it is named because of it's commonality in tobacco, it is also found in tomatoes, cucumbers, and several types of ornamental flowers. It is different because unlike a lot of plant diseases, it won't kill your plant. However, it does stunt growth and reduce yields. It is identified by light green and dark green spots on leaves, usually the younger ones. It can also cause a slight wrinkling in the leaves. To get rid of the virus, you must remove the infected leaves, washing your hands between plants so as to not spread the virus. Rotating host plants for no less than two years away from infected soil is necessary as well. In recent years, there have been breeds of plants that have been bred to be resistant to mosaic virus, so looking for these breeds may benefit you if you've had this problem in the past.

Fusarium wilt is a caused by a fungus that is common with many garden crops, especially tomatoes. It is identified by the yellowing and eventually browning of leaves on one side of the plant. Leaves then begin to die off and eventually the plant follows suit. The problem with fusarium wilt, besides causing plant death, is that it can survive in the soil for several years. This makes rotating crops isn't effective in prevention. The best ways to prevent fusarium wilt are to plant disease resistant plants primarily, and secondarily to remove infected plant material and to use fungicides. It is important to note too that the fungus lives in the soil and likes soils that are high in moisture and drain poorly. another way of preventing fusarium wilt is to build up your soil so that it drains properly, making it a less than desired environment for fusarium wilt.

Sooty mold is another disease that does little to no damage to plants, other than cosmetic damage. It is named after its dark colored mold spots that appear on plants like azaleas, laurels, gardenias, and camellias. It is caused because of insects that suck the honeydew sap out of the plants, like aphids. Organic control can be done with neem oil which kills the insects as well as the mold. For those who don't worry about using organic means of control, diazinon is a common pesticide used to control the insects that cause the infection. Fungicides can be used to kill the mold.

Blossom end rot is common, especially with tomatoes. It is identified by a soft reddish coloration that starts in mid to late summer. As the rot stops, the area affected becomes sunken in. Fruits infected with this disease usually fall off early, making them unusable or unsellable. The most common cause of blossom end rot is low calcium in the soil. Fertilizing with bone meal can solve this problem. Fungicides can also help lessen the effect.

Asparagus crown rot can cause a lot of problems in your asparagus plot. It is identified by yellow-orange spots on the asparagus spike which grow and eventually shrivel up. They can cause significant losses in your harvest, whether your growing them to eat or to sell. Mefenoxam is the primary fungicide used to control crown rot.

Bacterial blight is a disease found in bean crops grown east of the Rocky Mountains. It is identified by lesions that look like burn marks that eventually grow larger. It can cause high losses and can be treated with fungicides.

Rust is identified by rust colored spots on the leaves of plants like green beans. These spots eventually open up and disperse spores into the air that can infect surrounding plants. Rust causes foliage death and can significantly reduce yields. Use of fungicides helps to control rust.

Corn smut is a devastating fungal infection found in the ears of sweet corn. It grows from the kernels in the ear, turning them black with a whitish shell. In the U.S. it makes corn unsellable, even though unaffected parts of the ear are still edible. In Mexico, however, corn smut is a delicacy.

Black rot is a devastating disease that affects several different types of fruits, vegetable and trees, but it is commonly found in plants like cabbage and kale. It is identified by blackening of the veins in the plant, keeping nutrients from being made available to the rest of the plant. Use of fungicides containing copper are somewhat effective in containing black rot.

The number of diseases that can effect your garden are too numerous to count. One disease can be caused by different forms of fungus or bacteria in different plants. The results are usually very similar though. Identifying and treating accordingly, along with methods of prevention will keep your garden growing and producing. Use this information to keep your garden, and yourself, healthy. Happy gardening!

Blight on a potato leaf
Blight on a potato leaf
Blossom end rot
Blossom end rot


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