White Powder Fungus

Disease Identification

• The powderlike fungal growth on plants is referred to as powdery mildew disease. The disorder is among the easiest to identify and one of the most common plant disorders that affects all plants from crops and fruit trees to shade trees, shrubs, ornamentals, grasses and cereals. As with all fungi, the spores of powdery mildew are also spread by air and water and start to germinate and cause disease under optimal growth conditions.

Favorable Conditions

• The powdery mildew disease-causing fungi are more productive in warm and humid weather. Succulent plant growth is infected first. Plants that are growing in crowded areas with poor air ventilation and high air humidity are highly prone to the disease. The excessive use of nitrogen-based fertilizers leads to a flush of succulent growth that becomes high target for pathogen growth. Plants placed in damp, shaded areas also invite infection.

Symptoms

• The disease starts with the appearance of white or gray, fine, powder-textured patches on upper sides of foliage. As infection progresses, these patches get larger and spread to foliage undersides, stems, flowers or fruit. The fungi extract nutrients from plant cells causing leaves to yellow, distort and fall. Flowers fail to bloom and new shoots are stunted. Often, discoloration of foliage and shoot stunting appears before the white spots.

Management

• Growing plants in well-ventilated, sunny and open sites is the first line of defense against the disease. When buying new plants, inspect them carefully as even a couple of infected leaves can create a widespread infection in other landscape plants. Start management strategies early by removing the initially infected leaves. Chemical control options include the use of copper- or sulfur-based products, thiophanate-methyl, triadimefon or myclobutanil.