Extension offices get busy this time of year with lots of calls and questions about problems in all kinds of plants, from ornamental trees and shrubs, to flowering ornamentals, to home gardens- you name it, we get called about it. One of the most common calls we get every year is in reference to leaf spots. Leaf spots have the potential to occur on all plants and can cause significant stress to a plant. Depending on their cause, they may or may not have long-term negative impacts on plant growth and production. Today, let’s talk about leaf spots resulting from disease- primarily fungal and bacterial pathogens.
Leaf spots have a number of causes including air pollutants, insects, bacterial diseases, and fungi, with fungi being the most common cause. Most of these causes are species-specific, so the fungi that causes leaf spot on one plant may not infect plants in another family. Determining the specific cause of leaf spots can be a bit tricky as each presents with different patterns. Typically, leaf spots occur on the lower, inner branches of the plant, where there is higher humidity and shade. Leaf spots can occur on the upper or lower parts of the leaf, and may vary in size, shape, color, and texture. Smaller leaf spots are new infections, while large leaf spots are older infections. Sometimes with older, larger spots, you might see signs of the pathogen such as fungal spores. Some but not all leaf spots will cause defoliation of the plant. Leaf spot pathogens often overwinter in leaf debris, so it’s critical that you remove leaf matter from your garden each fall to help prevent their spread. During the growing season, most pathogens are spread by wind and splashing rain or irrigation and require high humidity and heat in order to become established. Most of the time, leaf spot will not harm your plants, unless it results in complete defoliation for more than one or two years in a row.
There are several methods to use to help manage leaf spot in a garden. First, and most important, is to remove fallen leaves from the area to help prevent re-infection the following season. Plants should be spaced appropriately based on their mature size to prevent overcrowding, which also facilitates pathogen spread. Proper pruning to encourage light and air flow into the canopy and base of trees and shrubs can help prevent leaf spot. When watering plants, be sure to emphasize watering at the base using drip tape or a soaker hose. Sprinklers or watering the foliage of the plants is a great way to spread disease and cause problems in your garden. Healthy plants are less susceptible to pest and disease damage, so be sure to soil test, correct pH and fertility, and follow care recommendations for your plantings. Should you have leaf spot resulting from a fungal disease, fungicide application can be helpful. The use of a fungicide will not cure infected leaves but may help prevent further damage. Fungicide selection and timing of application will be specific to the pathogen causing the leaf spot disease, so consult with your local Extension office for recommendations. Should you need additional help with leaf spot diseases, please contact us at uge3181@uga.edu or 706-359-3233
