Powdery Mildew Treatment and Prevention: An Overview

Powdery mildew fungus can be seen on a wide range of native and cultivated plants, garden plants, and turfgrass species. In general, it is not regarded as a major grass disease. Powdery mildew may be found on a wide range of turfgrass species wherever turfgrass is planted. Extreme infestations of Kentucky bluegrass are most common on turf growing in shady locations from spring through fall when weather is moderate, and relative humidity is high.

Powdery mildew is caused by many fungi types. Although most fungi affect only one or two plants, certain powdery mildew species target a large variety of plants. Powdery mildew fungi are all obligate parasites that require living tissue to develop and thrive. The fungus survives in greenhouses by spreading from damaged plants to fresh plants of the same crop. If the crop is not cultivated for many weeks, the fungus dies, and damaged plants must be introduced into the greenhouse to re-establish the fungus.

Outdoors, fungal structures develop on leaves and twigs, allowing the fungus to survive the winter. The fungus Erysiphe graminis causes powdery mildew on grassland. When climatic conditions are ideal, the fungus develops vast numbers of asexual spores called conidia on the surface of diseased leaves, giving them a “powdery” look.

Symptoms of Powdery Mildew

The fungus is initially noticed as isolated wefts of thin, gray-white, cobwebby growth on the top surface of leaf blades. This growth gets increasingly thick and frequently covers the whole leaf surface, giving the impression of having been dusted with talc or flour. When the condition worsens, the entire turfgrass stand may turn a dull white or light green color. Severely diseased leaves often become yellow and wither, resulting in a weakening of the stand.

Favorable Weather Condition

Powdery mildew spores normally blow into your garden, but if you’ve experienced powdery mildew in the past, fresh outbreaks may emerge from inactive spores in old vegetative material or weeds nearby. Powdery mildew, unlike many other fungal infections, thrives in warm (60-80°F / 15-27°C) dry regions. However, it does require relatively high humidity to proliferate. It spreads more slowly in colder, wet places, and it is also hindered by temperatures above 90°F (32°C). It also has a greater impact on plants in shaded places than on those in bright sunlight.

Control and Prevention

Planting shade-tolerant cultivars in shaded regions are the most effective way to reduce powdery mildew in the grass. A blend of Kentucky bluegrass, tall fescue, and fine fescue is ideal. Turf grown in the shadow consumes less nitrogen, saves water, and is less tolerant to low mowing. For darkened areas, management strategies should be altered accordingly.

To promote roots and prevent leaf moisture, water thoroughly and infrequently. Avoid light, frequent watering, and avoid irrigating shortly before or after sunset or dawn since this prolongs the leaf wetness period, which promotes disease development. Powdery mildew can be controlled by pruning, removing, or carefully positioning trees and shrubs to maximize light intensity and airflow. Avoid excessive nitrogen fertilizer and cut trees or shrubs carefully to enhance airflow and sun exposure for cultural management. Fungicides are rarely used; however, they may be used if the condition is serious.