Page 86 - AG 7-2011 Revised 2016

Powdery Mildew Powdery Mildew
on turf grass

Photo Courtesy of UNIVAR Photo Courtesy of UNIVAR

Powdery mildew is a common disease in the California landscape. Many landscape
plants are susceptible to powdery mildew, especially roses. It is easy to recognize the disease
on most plants by the light-colored powdery spores that form on shoots, both sides of the
leaves, and sometimes flowers. Infected leaves drop prematurely and leaves and shoots may
become distorted and discolored.

Powdery mildew is a fungus that requires living tissue to grow. The fungi grow as
thin layers of mycelium on the surface. Mycelium is the vegetative part of a fungus made of
threadlike tubes.

Powdery mildew spreads as wind-borne spores. Spores do not need water to germinate;
they actually die in water. Powdery mildew survives only on plant tissue and dormant buds and
does not survive in the soil.

Blight Fire Blight

Photo Courtesy of Corky’s Pest Control Photo Courtesy of Corky’s Pest Control
Brian Rineberg Brian Rineberg

BACTERIAL BLIGHT
Common bacterial blight appears on leaves as small, water-soaked spots and/or light green
areas which eventually turn brown. These irregularly shaped spots are bordered by a lemon-
yellow ring, which is an identifying feature of blight. The spots may grow together, resulting
in the death of the leaf and eventual defoliation of the entire plant. Heavily infected seed may
shrivel and germinate poorly.
Like most bacterial diseases, common bacterial blight occurs in conditions of high moisture and
humidity. Because of dry summers, this disease is not common in California.

FIREBLIGHT
Fireblight is a bacterial disease most often seen in ornamental pears. This systemic infection
spreads most rapidly in warm, wet bloom periods from water splash, and on bees and ants
moving from overwintering cankers to blossoms. Sporadic branches or the entire plant are
killed, but infected plants may last for years.

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