The Most Common Plant Diseases

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Plant diseases are caused by either environmental factors, such as moisture and fertilizer, or by other living organisms, such as fungi and bacteria.

Here are some tips for preventing most types of plant diseases:

  • Infected plant material should be removed from the garden area as soon as a disease is noticed. Either burn or dispose of the infected plants. Do not put diseased plant material in the compost pile.
  • When purchasing transplants, look for healthy plants that do not have any blemishes or spots on the leaves or fruit. Select disease-resistant plants when possible.
  • Use a drip or soaker system to water plants instead of an overhead watering system. Keeping plant leaves dry will help reduce the instances of mildew, rot and blight.
  • Do not overwater plants. Most plants prefer to dry out between watering.
  • Provide plants with plenty of air circulation. Prune plants so that air flows between branches and provide sufficient space between plants.
  • Do not touch an infected plant and then touch other plants in the garden. Hands and tools should be washed after handling an infected plant.

There is a long list of plant diseases. Here are some plant diseases that are commonly found in the home garden:

Root rot is a common disease that is caused by soil borne pathogens. Signs of root rot include wilting leaves, stunted growth and yellowing of the plant. The major cause of root rot is overwatering. Too much water makes it difficult for the roots to get air and causes the plants to drown.

Powdery Mildew affects a wide variety of plants and can be devastating to squash, beans, rose and lilac plants. This disease shows up on plant leaves as a white or gray powder after a long rain spell or during times of high humidity. It quickly spreads to the stems, flowers and fruit. When the mildew appears, wash the leaves with a solution of 1 teaspoon mild dish soap mixed with 1 quart water.

Late Blight is a disease that lives in the soil and attacks tomatoes and potatoes causing black spots on the fruit and leaves of the plant. Blight is most prevalent during cool, wet weather and cannot survive in hot and dry conditions.

Rust is recognizable by the powdery masses of orange, purple or black spores on the underside of leaves. The rust may leave a gall, or bump, on the leaves.

Black Spot attacks roses with its black spots that cause the leaves to turn yellow. Remove these black spotted leaves from the plant and any leaves that have fallen to the ground. At the end of summer, remove any diseased laves and canes. To prevent further instances of black spot, plant roses in full sun and keep other plants away from the rose bushes to provide air circulation.

Damping Off is a disease that prevents seeds from germinating and causes new seedlings to rot at the soil line. Damping off is caused by over-watering. When planting seeds, water well when the seeds are planted and let the soil dry slightly before watering again. A daily mist with chamomile tea or worm compost tea can help prevent damping off.

Fusarium Wilt attacks tomatoes, peppers, potatoes, peas and melons. With fusarium wilt, either the top of the plant or the lower leaves will wilt during the day and slightly recover at night. After a time, the entire plant will wilt. At this point, the plant will perform poorly or quit producing entirely.

Blossom End Rot affects the blossom end of fruits. It starts as a small spot at the spot where the blossom was attached to the fruit and grows into a large dark, leather-like lesion as the fruit grows. Heavy rains, drought or root injuries can result in a lack of water and calcium getting to the plant leaves. Hot and dry weather may also be a culprit due to the rapid rate at which plants grow and lack of water.

Most plant diseases can be avoided with proper care. Maintaining good plant health, keeping the leaves dry and not giving plants too much water will help avert most diseases. When problems do occur, remove the affected parts of the plants from the garden.

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Last Updated: November 4, 2012
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About Coletta Teske Coletta Teske has 25 years' experience in tech journalism, as well as home and gardening topics. She has freelanced for Fortune 500 companies such as Boeing and Microsoft, published more than two dozen computer books for Prima Publishing and Macmillan, and worked as a freelance correspondent for West Hawaii Today. Coletta has been an avid gardener since she was 2 years old. While living in Hawaii, she achieved a lifelong dream of becoming a certified master gardener.

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