Integrated Pest Management
Controlling Plant Diseases in the Home Garden
Diseases of vegetables, flowers, and other plants are caused by microorganisms, including fungi, bacteria, viruses, mycoplasmas, and nematodes. These organisms are microscopic and, therefore, are not as easily recognized as are the insects or other pests. However, the results of these microorganisms in our gardens can be very devastating. Control of plant diseases can determine the success or failure of a garden and can add immeasurably to the pleasure derived from the garden.
All plants are subject to disease. The average home gardener may have only one or two different diseases to contend with during the season. However, there are over 50,000 different plant diseases known in the United States. These diseases may range from leaf spots to the destructive wilts or rots which kill the plant before harvest. The number and severity of diseases varies greatly from year to year depending on environmental conditions, susceptibility of the host plant, and abundance of the causal organism.
Plant diseases can be controlled by using a combination of cultural, biological, and chemical procedures. Once disease-causing organisms infect your plants, very few treatments will cure the disease. Therefore, it is essential that diseases be prevented before infection rather than trying to eliminate them after infection. The application of the following practices will greatly improve your chances for a healthy, bounteous garden.
- Select a suitable location for planting your garden. The site should have 8 to 10 hours of direct sunshine per day. Avoid areas with a high water table or heavy clay soils since they favor root disease. The soil should have adequate soil fertility and the proper pH (6.0 - 7.5), although gardens can be grown successfully in soils with higher pH.
- Practice crop rotation in your garden plot. If possible, change your garden location occasionally. Closely related crops from the same group should not be planted in the same area for two to three years. Remove or destroy all dead and diseased plant material in the fall. Healthy crop residues can be composted and returned to the garden. These rotation and sanitation practices will reduce the risk of disease-causing organisms that have built up on previous crops. Crop rotation groups:
- Cucurbits (cucumber, squash, cantaloupe, watermelon)
- Solanaceous (tomato, potato, pepper, eggplant)
- Crucifer (cabbage, broccoli, cauliflower, radish, turnip)
- Corn (sweet, popcorn)
- Select disease resistant varieties where available. Resistant varieties are less likely to be seriously infected or killed with a disease, but they are not immune. Furthermore, a variety may be resistant to one disease but susceptible to another. Check with your local garden center or nursery about adapted, resistant varieties. Use only certified disease-free tubers. Do not save tubers from the previous year.
- Do not plant seeds too deep. Deeply planted seeds often rot before they germinate. Treat seeds with a fungicide such as Captan or Thiram to prevent damping off. See Plant Disease Control Bulletin #9.
- Buy only disease-free transplants from a nursery or garden center. It never pays to buy questionable transplants, no matter what the price. This is especially important with strawberries and raspberries.
- Fertilize your garden on a regular basis and according to soil test results. Weak or nutrient deficient plants are more subject to disease. Most gardens will require an annual application of nitrogen.
- Water properly. Maintain an even water supply and avoid dry-wet fluctuations. One of the most common causes of disease in our area is overwatering. Too much soil moisture favors root diseases.
- Control weeds in and near the garden. They provide the primary source for several virus diseases. They also harbor insects which spread the viruses.
- Destroy diseased plants as soon as you observe them in the garden since they may serve as a source of pathogens to adjacent healthy plants. Remove and compost crop refuse as soon as possible after you harvest. This helps to eliminate disease-causing organisms which could overwinter in crop debris left standing in the garden. Diseased plants should be discarded and not composted.
- Some plant varieties may require fungicides for control of diseases. However, before indiscriminately applying a chemical, be sure it is the proper chemical for the disease and that it is labeled for use on that plant. Follow label directions explicitly.
These practices will help you avoid destructive plant diseases in the home garden. Contact your county agent for more information concerning specific plant diseases and chemicals that may be used for their control.