Minimizing Diseases in Vegetable Gardens

Plants sometimes get sick. Vegetable plants usually are capable of fending off disease-causing bacteria, viruses, and fungi. But if conditions favor the disease and your plants are weak, the disease sometimes gains the upper hand, often leading to early death of the plants.

The tips below will help you minimize the effects of plant diseases on your garden by employing two basic strategies:

  • Keep plants as strong and healthy as possible.
  • Minimize the conditions that favor disease and its spread.

Choose resistant or tolerant varieties.
This is the easiest and most important way to reduce diseases in your garden. In seed catalogs you will often see abbreviations describing the resistance of a variety to a particular disease. For example, VF means that the variety is resistant to Verticillium and Fusarium wilts. PM means that the variety is resistant or tolerant to powdery mildew.

Resistant varieties resist infection by a particular disease agent and show little or no disease. Tolerant varieties may show symptoms of the disease, but still yield the same as resistant varieties or susceptible varieties protected by pesticides.

Buy treated seed.
Seed may come pretreated with a dusting of fungicide. This coating will help prevent the seed from rotting in the soil before germination and help protect the emerging seedling from a harmful "damping off" pathogen that girdles and kills young plants shortly after they emerge. If seed rot or damping-off has been a problem in your garden, treating seed with a fungicide will help.

Make sure seeds, transplants, and propagating material are disease-free.
Start with healthy plant material to help plants get established quickly. Unhealthy plant material will never yield as much as healthy material. Worse, plants may die while they are still young. Reputable seed companies sell only disease-free plant materials. They treat some seeds with hot water to remove infectious agents. They test others to reduce the risk of seed-borne viruses. When shopping for transplants or other propagating material, take time to examine the plants to make sure they are healthy and vigorous. If you save your own seed, harvest it from healthy plants and dry it thoroughly. Store seed in airtight containers in a cool, dry place.

Choose a sunny, well-drained location.
Most vegetable crops thrive in full sun. Shady, poorly drained sites produce weak, spindly plants that are easy targets for disease organisms. Even if such plants survive free of disease infections, they will not yield as much as strong, healthy plants.

Improve the soil.
When your only choice for a garden site has heavy, wet soil, plant in raised beds or ridged rows so that the soil around your plants' roots won't be waterlogged. Heavy, wet soils discourage healthy root growth and encourage root rots. If you plant a garden on a slope, build terraced beds to reduce soil erosion over delicate, young plants and newly sown seed. Soils that are dry and sandy can be mulched with straw, grass clippings, black plastic, or other materials to retain moisture. A soil that is favorable to healthy root development supports the growth of healthy plants.

Water plants carefully.
For best growth, plants usually require about 1 inch of water per week. If you don't get enough rain, water your garden. Water plants in the morning so that the foliage dries quickly. This reduces the spread of disease. Avoid using sprinklers if possible because they promote the spread of leaf, flower, and fruit infections. Trickle irrigation is a better choice because it delivers water directly to the soil without getting the rest of the plant wet. It also doesn't splash soil onto the plants, which can move pathogens from the ground onto the plant. (Mulches can also help reduce soil splashing.)

Don't over- or under-fertilize.
Plants that are fertilized properly at planting and during the season will grow better and be healthier. Use a complete and balanced fertilizer or incorporate well-rotted manure or rich compost into the soil. Avoid over-fertilizing because it can damage roots.

Space plants to allow air circulation.
High humidity and moisture favor the development of plant diseases. Allowing enough room for plants to grow and for air to circulate around mature plants reduces humidity and encourages rapid drying of plants after rain.

Clean up debris.
Always remove and destroy or discard (in the trash) plant material that shows signs of disease. Work in the garden when plants are dry because moisture on plants aids the spread of diseases.

Unless you have an active, hot compost pile, composting may not effectively eliminate diseases from plant residues under New York climatic conditions. At the end of the growing season, clean up all crop residues. Disease agents overwinter in debris and may infect new plants the following season.

Active composts should suppress pathogens that are often found on leaf material. Composting these plant parts is highly recommended. Diseased tubers, bulbs, and similar plant parts, on the other hand, should be discarded and not composted. These plant parts can survive longer periods in the compost pile before breaking down and may actually begin to grow within the compost pile.

Plant a fall cover crop.
After cleaning up the garden, sow a cover crop such as winter rye that will grow that fall and protect the topsoil during winter. The following spring, plow the cover crop back into the soil to enrich it with fresh organic matter. Cover cropping can help reduce populations of soil-borne disease agents. Noninfectious microbes flourish when cover crops are returned to the soil and tend to inhibit the disease-causing microbes.

Rotate crops.
Successive plantings of one crop family in the same area promotes the buildup of disease agents in the soil, making disease problems more severe over time. Rotate plants to different areas of the garden to help reduce losses caused by soil-borne disease agents. Avoid successive plantings within crop families, such as the cabbage family (cabbage, broccoli, cauliflower, etc.), the squash family (winter and summer squash, melons, cucumbers, etc.), and tomato family (tomatoes, potatoes, eggplant, and peppers).

One of the best ways to reduce disease damage is to choose vegetable varieties bred for disease resistance, such as 'Cornell's Bush Delicata' winter squash.

This straw mulch keeps soil from splashing on the lettuce and tomato leaves when it rains, keeping the crops clean and reducing the spread of foliar diseases that overwinter in the soil.

Drip irrigation delivers water right where plants can use it: to the soil. Sprinklers wet the leaves, which can encourage the spread of plant diseases.