In the spring, the trees had powdery mildew, which I treated with neem oil. In spring, these resting structures break open, releasing spores that are spread by the wind. Different from typical funguses, it doesn’t need moisture to thrive on plants. Extension is expanding its online education and resources to adapt to COVID-19 restrictions. Steve Nix is a natural resources consultant and a former forest resources analyst for the state of Alabama. However, because it’s still a fungus, it’s made up of spores that fly through the air due to wind and land on … Choose disease resistant varieties for new plantings or as replacement plants. Symptoms are most commonly found on the upper side of leaves, but can also infect stems, buds, flowers, and fruit. Most prevalent when outdoor conditions consist of cool temperatures with high humidity; however, it can be seen in warm, dry conditions as well. Where important plants have a history of powdery mildew infection, treat them preemptively, before the fungus appears. Do not compost infected branches or leaves. Young plants and new growth are usually more severely damaged than older plants, leaves, or branches. Trees can be infected by different fungi. Spray wettable sulfur onto affected leaves at the recommended rate specified by the label. Powdery mildew is a common fungal disease that is most aggressive during the late summer and early fall months. Powdery spores are produced in leaf spots throughout the growing season. The spores will remain in the compost and may infect other plants. Disease is often most severe on young leaves and green shoots. Sulfur (but not for sulfur-sensitive plants such as viburnum). Additional methods for controlling powdery mildew: Commercial fungicides will kill powdery mildew, but many experts advise using these toxic chemicals only on specimen plants that are highly prized since the fungus rarely kills trees. White to gray, powdery spots, blotches or felt-like mats form on leaves, stems and buds of infected plants. Family Erysiphaceae. They must be applied before disease becomes severe. Powdery Mildew Fungus on Trees. Regents of the University of Minnesota. The disease is worse on shaded plants or plant parts with little air movement such as interior or lower branches. Most powdery mildew fungus on trees release overwintering spores when conditions are moist. The stress caused by Powdery Mildew also makes the tree more susceptible to other diseases and insect infestations. The powdery mildew fungus grows into the plant to steal nutrients. Prune trees and shrubs to improve air movement between the branches. Spread of the disease is reduced by rain or irrigation. Powdery mildew disease is caused by many different species of fungi, with Erysiphe cichoacearum reported to be the most common culprit. University of Minnesota Extension discovers science-based solutions, delivers practical education, and engages Minnesotans to build a better future. Do not overcrowd plants. Choose disease resistant varieties for new plantings or as replacement plants. Avoid excessive pruning of infected plants during the growing season. Tolerate powdery mildew. Fungicides can be used to protect highly susceptible and prized ornamental shrubs like roses or ninebarks. Trees most commonly affected by mildew include linden, crab apple, catalpa and chokecherry. Fertilizer will cause the tree to produce young shoots which are highly susceptible to powdery mildew. Use size at maturity as a spacing guide when planting. Though mostly a cosmetic disease, severe powdery mildew infections can cause the Ligustrum tree’s foliage to become distorted and weaken the overall health of the tree. 2020 Do not fertilize infected trees and shrubs unless it is recommended by a soil test to correct a nutrient deficiency. Chemical fungicide treatments that kill powdery mildew include : Sulfer is perhaps the most common fungicide for powdery mildew. Powdery mildew does not significantly affect the health of the tree or shrub and does not require management. Fortunately, although the disease is disfiguring, it rarely kills a tree. It may not be necessary to treat the fungus at all, but certain measures may prevent it from becoming prevalent. In some plants, leaves turn purple to red around the infection. All rights reserved. Spores spread by wind and start new infections within the plant or in neighboring plants. Powdery mildew is rarely a tree killer, but it can disfigure specimens in the landscape. Adequate spacing improves air circulation and reduces powdery mildew infection. White to gray powdery spots, blotches or felt-like mats form on leaves, green stems and buds. What is Powdery Mildew? To control Powdery Mildew, spay the tree with Bi-Carb Old Fashioned Organic Fungicide which is certified for organic gardening. The white growth is actually the result of millions of tiny fungal spores. It is a product of moist conditions and is usually seen in the wetter spring and fall seasons. The powdery appearance comes from millions of tiny fungal spores, which are spread in air currents to cause new infections. The disease can significantly affect the look of ornamental plants like roses and purple-leaved ninebark shrubs. Infected leaves may be cupped or twisted at the site of the infection. Sulfur (not for sulfur sensitive plants like viburnum). Once severely infected, leaves may turn yellow and fall prematurely during the growing season. Q: I have Bing and Royal Ann cherry trees, both about 5 years old. A downy white fungal growth, powdery mildew attacks a wide variety of trees and shrubs as well as ornamental plants, indoors or out. Almost any tree species can be affected by powdery mildew, but the most common are maple, basswood, dogwood, lilac, magnolia, crabapple, catalpa, and oaks. Powdery mildew resistant varieties are available for many ornamental shrubs. Once dryer weather returns, the fungus usually retreats. Powdery mildew needs humid conditions to start new infections. Young leaves, water sprouts and green shoots are often most severely affected. The disease is often most severe on young leaves, water sprouts, and green shoots. Powdery mildew is a fungus that appears on the leaves of plants. During the growing season, prune only to remove severely infected shoots. In Minnesota, powdery mildew has been observed on the following trees and shrubs. The disease is most severe on plants or plant parts in shaded areas with poor air movement (interior or lower branches). Other species of powdery mildew survive the winter as a dormant fungus in the infected buds or shoot tips. How to Identify Powdery Mildew Damage. These spores start new infections on succulent, new growth. Powdery mildew does not cause significant damage to the health of the tree and does not require management. But avoid excessive pruning of infected plants—do your pruning during inactive periods. Rebecca Koetter and Michelle Grabowski, Extension educator. Prune the tree or shrub during winter months to increase light penetration and improve air circulation throughout the canopy. Mildew-resistant cultivars are available for many plants. Do not use sulfur on walnuts, as injury may occur. Powdery Mildew, Blumeria graminis, is a common and relatively recognizable disease affecting a wide range of host trees.This disease infects plants during times of high humidity, most often in the spring. Powdery mildew is a common disease that appears as a white powdery substance on a tree leaf surface. In spring, the chasmothecium rupture to release spores that are then spread by the wind. ; Powdery mildew usually covers the upper part of the leaves, but may grow on the undersides as well. Powdery mildew is a disease which is common on many ornamental trees and shrubs, including dogwoods. Do not overcrowd plants. Infected plants may appear to be sprinkled with baby powder or covered in cobwebs. In some plants, leaves turn purple to red around the infection. Don't plant trees in heavily-shaded areas and provide plenty of space for air movement and growing room. The University of Minnesota is an equal opportunity educator and employer. Although any tree can get this common disease, the ones that are most commonly affected are oak, maple, dogwood, magnolia, catalpa, and crabapple.