Recently our region has been stuck in a pattern of frequent late afternoon and evening thunderstorms. This frequent rainfall, combined with high humidity, has created the perfect environment for plant diseases, turning our lawns, landscapes and gardens into a fungus heaven. As a result, gardeners need to keep a close watch for symptoms of foliage disease, such as brown, red, purple, or yellow spots on plant leaves.
How fungal diseases develop
Most diseases that attack plant leaves are caused by fungal pathogens. Almost every kind of tree, shrub, flower, vegetable, fruit and turf grass is susceptible to at least one type of fungal leaf disease. Like insect pests, most plant diseases only attacks a very narrow range of plant species and will not spread to everything in your yard. For example, while the disease on your tomato leaves can spread to other tomato plants, it cannot spread to your crape myrtle or lawn.
Disease-causing fungi typically spread by microscopic airborne spores that require several hours of interrupted wetness to germinate, infect, and colonize plants. As the spores blow around in the wind, some will land on a susceptible plant species by random chance. If the leaf or other plant part that the spore lands on is dry, the spore will not stick and can’t germinate because there is not sufficient moisture. But, if the leaf or other plant part is wet from rain, irrigation, or dew, the spore can stick to the leaf, germinate, and then penetrate the plant tissue, causing infection. This is if the role moisture plays in disease development and the reason it is important to avoid wetting plant leaves when irrigating.
Prevent fungal diseases
The good news about most foliage diseases is they only affect the aesthetics of the plant. Foliage diseases rarely threaten the health of trees and shrubs and usually do not require treatment. There are a few exceptions so it is always a good idea to have disease problems correctly identified. Also, foliage diseases can be more damaging to young plants, fruits, vegetables, and lawns and should be identified as soon as they begin to determine if treatment is needed.
Foliage diseases can be minimized through proper cultural practices such as selecting resistant varieties, proper irrigation, soil and nutrient management, pruning, and spacing. Practices and conditions that increase fungal disease problems include poor air circulation that result from overcrowded plantings, poor water drainage, excessive irrigation, and too much dampness due to rainfall. Not all plants are equally susceptible to foliage diseases. When selecting plants for your garden or landscape, research which varieties are resistant to common diseases and look for these when shopping.
Manage fungal diseases
Avoid working in your garden or mowing your lawn when plants are wet. When you handle wet plants, you may be spreading the spores of fungal diseases from plant to plant, increasing the chances that they will find a plant or location where conditions are favorable. Wait until plants have dried completely before you handle them.
Keep your garden clean and well-weeded. Weeds can play host to diseases that may not affect them, but your garden plants may not be so lucky. Weeds are also a good place for insect pests to hide out. Remove rotting leaves and trash. Dispose of diseased plant parts away from your garden; do not introduce them to your compost pile.
Water plants properly. Don’t spray your garden with water and try not to wet the leaves of your plants when watering. Do not overwater; excessive moisture is the most favorable atmosphere for pathogens to breed.
Healthy plants are naturally able to resist diseases. When shopping for plants inspect leaves for spots or yellowing; only purchase plants with clean, green foliage. If needed, fungicides can be sprayed to control most leaf diseases. To be effective, these products must be applied as soon as symptoms begin. Have any plant disease identified before treating to determine the best product for control and cultural practices that will help limit the disease’s spread.
For assistance identifying and managing plant problems, visit http://ces.ncsu.edu, where you can post your questions via the ‘Ask an Expert’ link, or contact your local Extension office. If you live in
Susan Brown is the horticulture agent with the N.C. Cooperative Extension in