Managing and preventing disease in the garden is not a simple task, especially because diagnosing plant disease can be difficult. Plant diseases can also be transmitted in a variety of ways—through the soil, the leaves, or even from seeds depending on the disease. And just like human illnesses, there are different types of diseases, which includes fungal, bacterial, or viral. The simplest way to manage plant disease is to take measures to prevent it in the first place.
In an integrated, ecological disease-management system, it’s best to explore cultural options of disease control before turning to chemical ones. Cultural methods include choosing disease-resistant varieties, practicing crop rotation, using drip irrigation, and maintaining proper sanitation (such as removing plant debris from the field).
The risk of plant disease can be reduced simply by selecting cultivars that are resistant or tolerant to pathogens that may be of concern in your area. This involves some research and an understanding of what diseases your garden may be more prone to, as many varieties may show resistance to one or two specific diseases.
Following spacing guidelines on seed packets or transplant tags allows for good air circulation, which helps prevent disease. Setting plants too closely together also allows disease to spread more quickly.
Rotating crops—that is, purposefully planting crop families in different areas of the garden from year to year—has many benefits, one of which is disease management. As many diseases are soilborne and can survive in the soil for many years, it’s best not to plant a crop from the same family in the same spot year after year. Plant diseases are often specific to particular plant families, so if you planted tomatoes in the east corner of your garden last year, it’s best practice not to plant any crops from the Solanaceae family (tomatoes, eggplants, peppers) in that section of the garden for a few years.
Planting when the soil is too cold may cause seeds to rot and may induce transplants to suffer shock (thereby making them more prone to disease). Refer to planting calendars for your region for recommended sowing and transplant dates.
Minimizing overhead irrigation, like sprinklers, is another way to reduce the spread of foliar disease. Using drip irrigation helps minimize the spread of foliar disease by keeping water off the leaves, as the water is applied right at the surface of the soil and doesn’t splash back up to the plant’s leaves. It’s also important to remember that water facilitates the spread of fungal diseases, so it’s best not to handle plants in the garden when they’re wet. For example, tomatoes are especially susceptible to the spread of fungal disease, and so you should try to avoid harvesting or handling the plants in the morning when they’re wet from dew.
Another easy way to prevent the spread of disease in the garden is to sanitize your tools and seed trays as often as possible, but especially after knowingly handling diseased plant material or between seasons. You can use steam, bleach diluted in water, or other sanitizing solutions to clean tools and seed trays.
Removing Plant Debris
It’s also best to remove diseased plant material from the field, and to clean up plant debris after harvest. For example, leaving the stalks of lettuce in fields can harbor disease, so you should compost the stalks immediately after harvest to reduce the risk of disease.
Reduce Weed Pressure
Weeds can harbor some of the same diseases that affect vegetables crops. They also reduce air circulation around the plants, creating humid, stagnant conditions that promote fungal diseases.
Some diseases are transmitted through seeds, and these are of particular concern to seed savers because pathogens that are on or in the seed can infect the next generation of seeds. For home gardeners, only collecting seeds from healthy plants is the most feasible way of preventing seedborne diseases from being carried forward to the next generation of plants.
Unfortunately, even following best practices can’t guarantee a disease-free garden. Local university extension offices provide helpful publications containing information on common diseases in your area and often hold plant disease diagnostic clinics. Identification of some plant pathogens is possible by becoming familiar with the common diseases of your area and their characteristic signs and symptoms, while other diseases require microscopic examination of diseased tissue or sophisticated laboratory techniques.
Refer to your local extension publications to help identify the common vegetable diseases in your region and strategies for managing them: