Creating a disease-proof garden
By Joan Allen - UConn Home & Garden Education Center
Featured Article - posted Tue., Mar. 26, 2013
Is it really possible to have a disease-proof garden? Well, no. But there are many things that gardeners can do besides using chemicals to minimize the impact of diseases, even in years when the weather is perfect for disease-causing organisms such as fungi and bacteria. Many plants, for both vegetable and ornamental gardens, are available in cultivars that have resistance or tolerance to common diseases. This is one of the most effective and easiest ways to keep disease at a manageable level. Now, before the planting season begins, is a great time to search out disease resistant selections for your yard and garden.
Rainy weather during the growing season is great for the development of many plant diseases. When combined with susceptible plant varieties, crowded planting conditions, or poor nutrition, this can lead to ideal conditions for disease development.
There are disease-resistant or -tolerant cultivars for many vegetables, fruits, perennials and even ornamental trees. Here are a few examples:
Prairie Fire crabapple: Resistant to scab, rust, fire blight and Japanese beetles.
Hybrid elms: Some are resistant to Dutch Elm Disease.
Lilac: Some are resistant to powdery mildew.
Rose: Many hybrids are resistant to blackspot.
Juniper: Some are resistant to cedar-apple rust, blight.
Phlox ‘David’: Powdery mildew resistant.
Jersey Giant asparagus: Resistant to rust, tolerant of Fusarium root & crown rot.
Stonehead cabbage: Resistant to yellows and black rot.
Trofeo green bean: Resistant to mosaic virus, halo blight, anthracnose.
Tomato: Many disease resistant choices.
Rhododendron: Resistance to root rot available.
When selecting tomato seeds or plants, look for the letters V (Verticillium wilt), F (Fusarium wilt race I), FF (Fusarium race I & II), and T (tobacco mosaic virus) following the name of the variety to select plants resistant to those diseases.
There are a variety of cultural practices that can help reduce disease development and spread. It is particularly helpful to cut down on the length of time leaf and plant surfaces are wet after a rain or irrigation. Many disease-causing organisms require a film of water for a certain length of time to start an infection. Adequate plant spacing will allow good air circulation around the plants and they will dry out faster after a rain or irrigation. Planting in full sun, which is required for vegetables and most fruits, will also aid in drying. The timing and method of irrigating is also important. Water at the base of the plants instead of spraying the leaves. If you’re using a watering method that will wet the leaves, the best time to water is in the early morning. During the day, the sun will dry the leaves. Wet leaves combined with cooler night temperatures are favorable to diseases.
Many root diseases are favored by poorly-drained soils because water takes longer to drain, favoring many wilt and root rot pathogens. If your soil is low in organic matter, its addition will improve the soil structure, moisture retention and drainage, and nutrient levels. A strong root system will be more resistant to both disease and drought. Encourage healthy roots by watering deeply (1-2” water) once a week instead of a little bit at a time more frequently.
Healthy plants are better able to resist or tolerate disease. The right amount of sunlight, water and nutrients will go a long way in preventing disease. To determine the amount of fertilizer needed for your garden, a soil test is recommended. Soil testing is available through the UConn Home & Garden Education Center. Information is available at www.soiltest.uconn.edu.
Sanitation is a very important component of disease prevention. This means the removal of any diseased plants and plant parts from the garden, both during and at the end of the growing season. Removing diseased tissue during the growing season helps prevent new infections from starting when fungal spores are produced, for example. Many pathogens overwinter in fallen leaves and dead plant material, providing a source of new infections in the next spring or summer, so a thorough fall cleanup can remove a significant source of problems.
Despite our best efforts, plant diseases will sometimes become a problem. There are a number of ways to control various diseases. One organic method is the use of compost tea. Briefly, this is made by steeping compost in water for a few days, filtering the liquid, and applying it to leaves or soil using a spray bottle or watering can. The beneficial microorganisms in the “tea” inhibit the growth of pathogens. Repeat applications may be necessary. Mixing finished compost into your soil will also have this effect.
If you have questions on plant disease control or any other home or garden topics, contact the UConn Home & Garden Education Center, toll-free, at 877-486-6271, visit www.ladybug.uconn.edu or call your local Cooperative Extension Center.