Long, sunny days and high temperatures provide two important conditions for rapid plant growth. Sufficient moisture is another requirement.
After a rainy springtime, July precipitation has been limited so far. In Dalton, only about a third of an inch has been recorded for the first three weeks of the month. Unfortunately, optimum conditions for growth of desirable plants can often also provide ideal conditions for infection and proliferation of plant diseases. Landscape watering during dry spells can add foliage moisture and humidity, further encouraging disease development.
A critical first step in management of landscape disease management is identification of. Eighty percent of all plant disorders result from the inability of a plant to adapt to its environment. Recognizing the problem, whether it is stress-related and/or disease-related, begins with being able to correctly identify the plant.
Knowing the plants that you are managing will suggest what environmental extremes the plant may or may not be able to tolerate, such as full sun, shade, drought, poor drainage, freezing, etc. Many stresses can be avoided with proper planting and maintenance. A stress-free plant is often better able to tolerate disease and insect pests.
The simplest solution is often the best approach when dealing with fungal diseases in the landscape. Most fungicides available to homeowners will not provide “curative” control.
In fact, most fungicides should be used preventatively and well in advance of an anticipated disease issue. Most recommendations entail applying fungicides on new spring growth because young, tender leaves and shoots are more susceptible to disease injury, and spring weather conditions are often ideal for fungal diseases to start.
Once a leaf is damaged with spots or necrotic lesions, that spot remains until that leaf falls off the plant, no matter how much you spray. Before spraying, it is usually a good idea to prune out the worst sections and then spray to protect the rest of the plant.
The portion of the plant affected often determines the course of action. Disease issues and general control alternatives can be lumped into three main categories: leaf diseases, stem and branch diseases, or root and vascular diseases. Leaf diseases, such as powdery mildew and fungal leaf spots, are not generally considered lethal. Plants that are otherwise healthy can tolerate significant leaf loss and will often be able to produce new leaves either midseason or next spring. As plants approach late summer or early fall, the loss of leaves is even less of a concern on deciduous plants since they will soon lose their leaves anyway.
Leaf diseases are often considered an aesthetic issue and it’s important to understand that, although the problem may look unsightly, it should not kill your plants. Leaf diseases are a stress factor, and, if compounded with other environmental stress over multiple years, could lead to a more serious outcome. However, the cause of plant death is usually not due to a leaf disease alone, and environmental stresses are often of greater concern.
Stem and branch diseases can often cause more permanent damage to a plant. Many fungal cankers and gall-forming diseases can spread to kill entire branches or, if they spread to the main trunk, may kill the entire plant. The key with stem and branch diseases is to scout susceptible plants frequently and catch the problem early. Often, the only solution is to prune out the affected portions of the plant to limit spread. Fungicides provide little help once stem or branch diseases have formed.
Root and vascular diseases are usually considered lethal diseases. These diseases kill plants either by impeding the flow of water-conducting vascular tissues inside stems or they cause roots to rot.
In either case, the permanent wilt-related symptoms are the result of a fungus blocking the uptake of water. If a plant is permanently wilted and doesn’t respond to normal watering, it’s likely the result of a root-rot or vascular-stem disease.
Fungicides will not cure plants infected with a vascular wilt. Often the best approach is to plant resistant varieties and to ensure plants are selected and installed according to their preference for soil moisture, sunlight, shade and drainage. With most trees and shrubs, it’s generally a good idea to plant their roots an inch or two on the high side to ensure good drainage.
The best tools for disease management are proper plant selection, good maintenance practices to minimize stress and identifying disease problems early. A good motto to follow is “if in doubt, prune it out."
Roger Gates is the agricultural and natural resources agent for University of Georgia Extension, Whitfield County. Contact him at firstname.lastname@example.org.