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Identification is job #1
Managing common landscape diseases by Paul Pugliese for CAES News
The most important part of landscape disease management is identifying the problem. Eighty percent of all plant disorders are the result of the inability of a plant to adapt to its environment. Knowing the problem begins with being able to correctly identify the plant.
UAC MAGAZINE | FALL 2020
Plant ID can clue you in to what environmental extremes the plant may or may not John Ruter, University of Georgia, Bugwood.org be able to tolerate, such as full sun, The key with stem and branch diseases is to shade, drought, poor scout susceptible plants frequently — such as drainage, freezing, for Seiridium canker on Monterey Cypress — etc. Many stresses and catch the problem early. Often, the only solution is to prune out the affected portions can be avoided with of the plant to limit spread. proper planting and maintenance. A stress-free plant is often better able to tolerate disease and insect pests.
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The simplest solution is often the best approach when dealing with fungal diseases in the landscape. The majority of fungicides on the market don’t provide “curative” control. In fact, they should be used preventatively and well in advance of an anticipated disease issue. Most recommendations will focus spraying fungicides on new spring growth because young, tender leaves and shoots are more susceptible to disease injury, and damp spring weather conditions are often ideal for fungal diseases to start. Remember, once a leaf is damaged with spots or
necrotic lesions, that spot is permanent 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 location of the disease often determines the course of action. Disease issues and general control options 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 often will 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. 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 the plants. It is true that leaf diseases are a stress factor, and, if compounded with other environmental stress issues over the course of 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 any environmental stresses should be of greater concern. Stem and branch diseases can often cause more permanent damage to a plant. For example, 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 — such as for Seiridium canker on Leyland cypress — 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.
