Apr 28, 20255 min read

7 Common Spring Plant Diseases

7 Common Spring Plant Diseases and How to Prevent Them

Spring is a wonderful time for gardeners because the garden comes back to life. However, with temperature fluctuations and spring rains, this time of year brings an increased likelihood of diseases and pests. Forewarned is forearmed. Here are some of the most common diseases we see in the spring.

Powdery Mildew

Powdery mildew is a group of fungal diseases characterized by a white powdery mat covering the leaves, stem, and flowers of a plant. The first symptoms are white spots on the plant, which expand to cover much of the foliage and flowers. Leaves can become twisted, stunted, or discolored. Flowers are abnormal and show damage. The fungus sucks nutrients from the plant, causing a general decline in the plant's health.

Powdery mildew fungus begins to produce spores when the temperature reaches 60 degrees. They disperse in the wind. Unlike most fungus, powdery mildew doesn't have to land on wet foliage to grow. If the humidity is high, that is enough for the spores to grow.

Powdery mildew grows on a large variety of plants. Some symptoms may differ by plant. For example, dogwoods show problems on their leaves, which become yellowish or reddish cast in summer or may develop reddish blotches or dead, scorched patches.

Prevent powdery mildew by choosing resistant plants. Make sure to give plants some space so that air circulates and lowers the humidity in the plant canopy. Crowded plants are more vulnerable. Prune the suckers off of dogwood, crape myrtle, and other plants because the succulent growth is especially vulnerable. The disease will infect suckers and spread upward toward the rest of the tree.

Powdery mildew is treated with a fungicide. The exact fungicide differs according to the plant species, air temperature, and time of year.

Anthracnose

Anthracnose is a disease that causes dark spots on leaves. These spots may spread, may become sunken, and may produce cankers on twigs and stems. Sometimes these cankers girdle the twigs and stems, potentially killing the plant. Affected leaves may fall prematurely, defoliating trees. Anthracnose is a problem when rains occur after plants have started producing foliage. When the rains stop, anthracnose generally disappears. Deciduous trees such as maple, ash, Chinese elm, oak, sycamore, and dogwood are especially vulnerable.

Treatment is difficult so prevention is key to keeping your plants healthy. Anthracnose overwinters in leaves and twig, so raking your leaves in the fall and early spring will help prevent it. When watering, do not get the foliage wet. Keep the water at the root zone. Water in the morning so the foliage has all day to dry. Avoid splashing soil on foliage because this is a key way anthracnose spreads. Plant resistant cultivars of trees that are especially vulnerable.

Leaf Spot

Leaf spot diseases are a problem in many ornamental trees. Generally, they do not do more than cause mild stress to the tree. Because the leaf spot diseases interrupt photosynthesis where they are growing, they can be a problem when most of the tree leaves have this disease. These leaves often fall prematurely. If defoliation happens several years in a row, it can cause the tree to decline. Trees with leaf spot are more likely to get other diseases and be attacked by pests.

Treatment is seldom necessary, but there are things you can do to reduce the likelihood of a serious infection. Plant resistant trees when possible. Space trees and other plants to allow air circulation around the plant. Prune trees to increase air flow and sunlight penetration into the canopy. Rake up and destroy the leaves and twigs from infected plants. Water trees at their base and do not get the foliage wet.

Rust

Rusts are fungal diseases named for the orange, yellow, or reddish areas of fruiting bodies that develop on affected plants. Each species of rust typically infects a small number of plants. Often, one plant is affected for sexual reproduction and another plant is affected for asexual reproduction. Both species must be present for the disease to flourish.

Rust is a threat when the temperature is mild and the foliage is wet. Spring rains or overhead irrigation allow the spores to develop and infect the tree or plant. Prevention of rust is similar to prevention of leaf spot. Rust resistant cultivars of vulnerable plants are available. Treatment requires frequent application of fungicides and may be hard to achieve in a residential setting.

Downy Mildew

Downy mildew is caused by a group of water molds. It starts as small, water-soaked spots on leaves. These spots are slightly yellow. The spots progress to become bright yellow, then brown. The actual appearance of downy mildew varies a lot by species, environmental conditions, and the type of downy mildew infection. Leaf defoliation may occur in severe outbreaks, weakening plants and trees.

Fungicides are used every 7-10 days to prevent downy mildew when the wet, cool days of spring make an outbreak imminent. Most of the fungicides that prevent downy mildew are not labeled for homeowner use, so you may have to hire a professional to administer them.

Root Rot

Abundant spring rains can cause problems with root rot. If the soil does not drain well, many plants will develop root rot because of the soggy conditions. Many plants are also vulnerable to crown rot as well. Leaves wilt and may turn dull green, yellow, red, or purplish. They do not recover when the plant is watered. Darker areas often develop on the bark at the crown and upper roots.

There is no treatment for root rot. Once the plant's roots rot off, it cannot take up water and will die. Prevent root rot by not watering excessively, do not get the trunk or stem wet when watering, and do not plant in areas with poor drainage.

Damping Off

Damping off is one of the most frustrating diseases for gardeners. One day your plant is a new seedling, the next day it is a shriveled, black thread. Water molds and fungus are the culprits. They attack the stem at or below the water line. The stem collapses, cutting off water and structural support to the plant above the collapse, and the seedling falls over and dies. Damping off is most prone to attack when cold, wet conditions occur.

Prevention includes keeping the soil moist but not soggy, using rubbing alcohol to sterilize tools, pots, and workspaces to kill the spores, and using germination mats to keep the soil warm. Seedlings quickly grow out of their susceptibility to this disease. However, once one seedling is attacked, the whole seedling tray will probably be attacked. Do not reuse plastic seedling trays that have been infected with damping off or it will keep attacking your seedlings.

Prevention Is Key

Spring diseases are frustrating. Almost all of them involve wet foliage. Use mulch to cover the soil around the plants. This prevents soil borne diseases from splashing on your plants. Space plants so the air circulates around them. Keep the soil in seedling trays warm and moist. If you follow these recommendations, your plants will be much healthier.