Vegetable Gardening (122 page)

Diseases differ from insects in that, with bugs, you can take action after you see them. With diseases, once you see symptoms, it's often difficult to stop the diseases from spreading. However, you can prevent or at least reduce most vegetable diseases by using good growing practices or by planting resistant varieties. Most vegetables have some varieties with disease resistance; see the chapters on individual vegetables in Part II for details. In the following sections, I provide useful methods for preventing and handling some common diseases.

Avoiding diseases with good habits

Here are some cultural practices that can help you avoid plant diseases:

Remove infected plants.
After you've identified a plant with a severe disease problem, yank out the entire plant. Even picking off infected leaves helps prevent a disease from spreading.

Avoid overhead watering.
Overhead watering can encourage foliage disease organisms to prosper. If you can't avoid this watering method, at least water early in the morning so plants have a chance to dry out before nightfall. Using drip irrigation or watering in furrows helps keep foliage dry (see Chapter 15).

Space plants properly.
Planting vegetables too close together reduces air circulation between them, a condition that favors disease and allows diseases to spread from plant to plant more readily. Keep your eyes open for developing problems.

Keep your garden clean and tidy.
Many diseases spread on plant debris, so rake up fallen leaves and remove dead plants. Also, keep the spaces under any containers clean. Removing diseased leaves can slow the spread of some organisms.

Rotate plants.
Don't plant the same vegetables in the same place year after year. Otherwise, you create a nursery for disease. Move things around as described in Chapter 16.

Mulch your beds.
A layer of mulch on the soil can act like a physical barrier, keeping disease spores in the soil and off the plants. See Chapter 15 for more on mulches.

Watching out for common diseases

The following list includes tips on how to prevent, identify, and treat (if possible) some common diseases that affect vegetables. Controls for diseases that are most troublesome for a specific vegetable are included with the description of that vegetable in Part II. Here are some diseases to keep an eye out for:

Damping off:
This disease attacks the bases of seedling stems, causing them to wilt and fall over. I discuss ways to prevent damping off in Chapter 13, which covers all aspects of growing vegetables from seed.

Powdery mildew:
This fungus coats leaves and flowers with a white powder. It's most common when days are warm but nights are cool. This disease is particularly troublesome to squash, cucumbers, melons, and peas. Controlling powdery mildew is difficult, but resistant varieties are available. The disease becomes less of a problem as the weather changes.

Some gardeners have had some success using a home remedy. Mix 1 tablespoon of summer oil and 1 to 2 teaspoons of baking soda in 1 gallon of water, and then spray the mixture often to protect new foliage. This mixture also is sold commercially under names such as Remedy. Some forms of neem oil also are registered for use on vegetables. A new biological spray called Serenade (
Bacillus subtilis
) contains a bacterium that attacks powdery mildew and other fungi.

Root rots:
A number of soilborne fungi cause plants to have basically the same damage — regardless of whether the soil is moist. Lettuce is notorious for dying like this. The best way to prevent root rot is to make sure that soil drainage is good and to avoid overwatering — let the soil dry partially between waterings. Otherwise, all you can do to control root rot is to remove the dead plants. Few other control measures are effective.