Common Plant Diseases in Container Gardens

Plant diseases are often named by the symptoms they cause. Some diseases affect only one type of plant or part of a plant, for example the leaves. Here is a list of fungal and abiotic plant diseases that might cause trouble in your container garden:

  • Fungal diseases: Fungi are the culprits in many plant diseases. Here are some tips on the prevention, identification, treatment of some common plant diseases that are caused by fungi:

    • Black spot: This fungus causes black spots on leaves and stems (. Black spot is most troublesome on roses, but it can also attack various fruiting plants. The disease is most common in warm, humid climates with frequent summer rain.

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      The best advice for preventing black spot is to plant resistant varieties. The second-best advice is to keep your rose planters clean. Remove plant debris after pruning, clean up fallen leaves, and pick off leaves that have spots or turn yellow. Also, avoid overhead watering, or at least water early in the morning so that leaves can dry out quickly.

    • Botrytis blight: Also called gray mold, this fungal disease overwinters on plant debris and is common on strawberries, petunias and other flowers. The blight is most noticeable as gray fuzz forming on old flowers and fruit, turning them to moldy mush, but it can also discolor or spot foliage. It’s most troublesome on older plant parts and in cool, humid weather. Make sure plants are properly spaced, and avoid overhead watering. Remove and destroy any infected plant parts.

    • Damping off: Damping off causes rot at the base of seedling stems, weakening them so they wilt and fall over. The best way to prevent the disease is to plant seeds in sterile potting soil and avoid overwatering.

    • Powdery mildew: This fungus coats leaves and flowers with a white powder. Powdery mildew is most common when days are warm but nights are cool. The disease is weather-dependent, so if you can keep plants growing vigorously through a disease cycle, they may recover just fine.

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      Control is difficult. Regular sprays of neem oil may help minimize infection. Rose growers have some success using a mixture of 1 tablespoon of summer oil and 1 or 2 teaspoons of baking soda in 1 gallon of water; you have to use the mix often to protect new foliage.

    • Root rots: A number of soil-borne fungi cause similar symptoms: Plants suddenly wilt and die, whether or not the soil is moist. Vinca is notorious for checking out like this. The best way to prevent root rot is to use fresh soil mix, make sure your pots drain properly, and avoid overwatering. Once root rot takes hold, most plants succumb.

    • Rust: This fungal disease forms rust-colored pustules on the undersides of plant leaves. Gradually the upper sides of the leaves turn yellow and the whole plant begins to decline. Space plants for good air circulation, keep the garden clean, mulch around the base of plants, and avoid overhead watering. Destroy infected plants.

  • Abiotic diseases: These are plant problems not caused by an organism, such as a fungus, insect, or bacterium. Rather, they are caused by nonliving factors such as light, temperature, and atmospheric conditions.

    Rule out abiotic diseases before treating plants with pesticides, which won’t do any good. Instead, follow the treatment plans outlined below for the specific disease.

    • Salt burn: Salt burn is caused by excess fertilizer salts building up in the soil. Leaf edges become. If the condition worsens, the whole leaf may dry up and drop, and tips of branches may die.

      Prevent (and treat) salt burn by flooding the soil in containers with lots of water, letting it drain, and repeating up to a half-dozen times. Just be sure the container has good drainage.

    • Sun burn: If the foliage on plants looks bleached, your plants may be suffering from sunburn. Most plants recover from sunburn: Just vow to harden plants off before exposing them to the elements.

    • Frost damage: Chill or frost damage usually appears as blackened foliage, especially on the most exposed parts of the plant. If a cold spell is predicted, protect tender plants by moving them to a sheltered spot or covering them with an old sheet. If plants are nipped by frost and just the top leaves are damaged, pick off the affected leaves and the plant may recover.

    • Wind and hail: Plants with large, tender leaves are most likely to suffer damage from wind and hail. Unfortunately, damage like this, which creates open wounds, sometimes leads to fungal infections. You can’t do much to treat damaged plants. If damage is limited to a few leaves, pick them off. However, if the whole plant is affected, all you can do is wait and hope the plant recovers on its own.

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