Pender Gardner: Wet weather promotes fungal diseases

Gardener

Spot on leaves caused by fungal pathogens are usually surrounded by a halo of yellow or reddish colored leaf tissue.

Submitted photo
Published: Thursday, August 29, 2013 at 14:58 PM.

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.



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