How to Avoid Plant Diseases
No matter how green your thumb, disease will eventually strike your garden. Understanding the reasons plants get sick helps you pinpoint problems within your landscape so you can enjoy watching your plants grow healthy and strong. How plants fall victim to disease is similar to what occurs when you get sick. Weakened plants are more susceptible to diseases that come their way, and problems quickly set in when the environment is just right.
Prevent diseases in your garden by keeping the following information in mind.
Plant locationMany disease problems spring up because plants are located in the wrong place. No matter how much care you provide, a desert plant growing in a wet spot is never going to be healthy and can fall victim to a wide variety of diseases, including Phytophthora, which is a fungus-like organism that attacks and shuts down a plant's roots, causing it to wilt suddenly and die. Before planting, research the sun and soil needs of each plant and make sure you will be able to provide for those needs.
Most plants do best in an area with good air circulation, so don't crowd plants when planting, but make sure to provide space between each plant. Spacing will vary by plant, but generally, small plants should be spaced 4 to 6 inches apart, small shrubs one to two feet apart, and large shrubs and small trees four to six feet apart. Adequate ventilation helps prevent foliar fungal diseases that thrive in close, humid locations, such as powdery mildew, which causes a white, powdery coating on plant foliage, and black spot, which leads to brown and black spotting on leaves and leaf loss.
The number one cause of unhealthy plants is improper watering. Underwatering weakens a plant and opens it up to disease. Overwatering leads to drowning roots, which causes root rot. Signs of root rot are wilting leaves even though the soil is wet, black and brown spotting on foliage and stems, and stunted new growth.
Water plants properly, and you'll have strong, disease-free plants. To give plants the right amount of water, check the soil before irrigating. One easy way to find out if your plant needs watering is to use a moisture meter (277-9988). This handy device come with a probe that you stick into the soil, and tells you on a scale of 1 to 10 if the soil is dry, slightly moist or wet. Many plants should be nearly dry before you water them in order to prevent root rot. Keep in mind, though, that some plants like wet conditions, so learning about your plant's moisture needs will help you water properly and prevent disease.
How you water is equally important. Don't water plants from overhead with sprinklers. Foliage that is constantly wet quickly develops fungal diseases like downy mildew,which causes mottled yellow and brown markings on leaves. To water properly and avoid damage to foliage, water at the ground level with a slow-running hose or soaker hose (Yardworks® 50' Soaker Hose, 274-1351).
Over-pruned or incorrectly pruned plants get shocked and weakened from not being cut back correctly, and this can lead to a wide variety of diseases. Before doing any cutting, research if your plant needs pruning and how much pruning is healthy for the plant.
Pruning tools can pass disease from one plant to the next. If you do prune, make sure to clean your pruning tools between each plant with a solution of one part bleach to nine parts water to prevent spreading disease. Use a quality pruning set and keep it sharpened to make clean cuts rather than tearing the plant tissues (Masterforce® Titanium Bypass and Anvil Pruning Shears 265-5955, 5956).
Certain plants are more prone to disease than others. Some tomatoes, for instance, are susceptible to infestation by fungal diseases, such as Fusarium and Verticillium wilt. Fusarium and Verticillium are fungal diseases that cause initial wilting and yellowing of lower plant leaves and eventual plant death. Luckily, many plants have hybrid varieties available, created by plant scientists by combining the best traits of multiple varieties of a plant. The result is a plant that is hardier and will resist disease better. Tomatoes that are resistant to these diseases are marked with VFN on the plant label. When plant scientists created VFN tomato hybrids, they used varieties that naturally had resistance to Fusarium and Verticillium.
Having too many of one plant creates what is known as a monoculture. Monocultures are more likely to be wiped out by disease. Since certain diseases tend to affect certain plants, having only one species of plant in a concentrated area can allow disease to spread rapidly and kill all the plants. By including several different kinds of plants in each garden area, it will be less likely that disease will kill off large numbers of plants.
Practice plant hygiene
Generally, a clean, tidy garden is less likely to create an inviting location for disease. While some plants, such as oak trees, do well sitting in their own leaf litter, other plants fall prey to disease if the planting area isn't kept clean. Camellias, for instance, require the area under the shrub to be free of fallen flowers. Rotting blossoms can cause camellias to develop camellia flower blight, which leads to flowers turning brown and falling prematurely.
When you do notice signs of disease in the garden, such as discolored or spotted foliage, leaf loss or stunted growth, promptly investigate the problem and treat with the appropriate remedy. If you use a fungicide, make sure to follow package directions carefully (Garden Safe® Fungacide3, 263-4966).
Keep in mind that some plants naturally change their appearance throughout their growth cycle, and such changes can look like disease. In the fall, for instance, the leaves of deciduous plants take on a dull sheen before they begin to brown in preparation for falling. Some plants even have leaves that change color several times throughout their growth cycle.
The key to disease prevention is researching your plants and giving them exactly what they need. Happy plants are strong, and strong plants rarely get sick.