A Leaf Fungus Is My Bing Cherry Tree From the Heat and Humidity

The Bing cherry tree (Prunus avium “Bing”) is a sweet cherry variety loved for its big, juicy, dark red fruit that ripens in the summertime. It also bears fragrant, white spring blooms and dark green leaves that turn bronze or gold in fall. Though it grows well in completely sunny places throughout U.S. Department of Agriculture plant hardiness zones 5 through 8, the Bing cherry is quite prone to powdery mildew, a fungal disease that strikes leaves in hot, humid weather. You can take a few steps to take care of powdery mildew and keep your cherry tree healthy and appealing.

Regarding Powdery Mildew Fungi

Cherry powdery mildew (Photosphere clandestina) thrives when daytime temperatures drop between 70 and 80 degrees Fahrenheit and the humidity levels soar over 90 percent. The fungi overwinter on fallen leaves or under loose tree bark, surviving inside of miniature, protective structures called cleistothecia. The cleistothecia release spores in the spring, and those spores spread to young cherry leaves through watering or splashing rain falls. Spore release typically lasts from about 30 days before grass break-up until after the flowers bloom.

Powdery Mildew Symptoms

Powdery mildew causes a white to light gray growth to form on the tops and undersides of leaves, frequently creating the leaf appear as if somebody sprinkled it with talcum powder. Luckily, the noninvasive fungal threads only develop on the surface of plant tissue. Despite this, the fungi may cause leaves to yellow and fall from the tree prematurely. New growth frequently looks stunted or distorted. The fungi occasionally appear on the fruit, ruining the quality and appearance of their cherries. While younger trees and young shoots are most exposed, powdery mildew can reduce the vigor, bloom and fruit yield of trees.

Cultural Practices

Powdery mildew fungi thrive in moist, shady conditions, so plant your Bing cherry in a place that receives sunlight. Even though the fungi prefer moderate temperatures, direct sunlight may kill the spores. Avoid giving your shrub applications of nitrogen fertilizer in late summer. Nitrogen promotes lush new growth that will be more susceptible to powdery mildew infections. Raking up and discarding all fallen leaves and lawn debris in fall helps get rid of potential overwintering sites. For small or localized powdery mildew infections, prune out affected plant tissue and discard in a covered garbage can. Do not compost the diseased material or you risk spreading the fungi to some cherry trees in your landscape. Increasing airflow throughout your tree helps reduce the humidity levels around the plant, therefore prune out busy interiors and surplus leaf. Pull your pruning shears into a solution containing 1 part household bleach and 9 parts water between each cut to stop spreading powdery mildew fungi to healthy foliage.

Neem Oil Software

Neem oil treatments can help treat mild to moderate powdery mildew infections should you carefully read and follow the directions on the manufacturer’s label. 1 product advocates mixing 2 tablespoons of neem oil focus on every 1 gallon of water. Use a small garden sprayer to cover the tops and undersides of leaves before the surfaces glisten with moisture. When powdery mildew disease is present, spray once a week until the symptoms disappear, and then continue spraying every 14 days to stop the disease from coming back. The same solution can help prevent powdery mildew should you spray every seven days to 14 days beginning just before bloom and continuing for as long as your region experiences warm, humid weather conditions. Neem oil is toxic to any bees you spray. Avoid making direct contact with all the pollinators by spraying in the early morning or early evening when the bees are not active. Avoid spraying cherry trees if the temperature rises above 90 degrees F or you risk injuring the leaf. Since neem oil may irritate eyes and skin on contact, wear protective clothing and goggles when mixing and spraying the solution.

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