Early symptoms include small, yellow flecks, they expand over time into raised pustules, yellow or orange, that rupture to release spores. Infected plants become yellow. Heavily infected areas become thin and exhibit clouds of orange dust when the foliage is disturbed. The rust pustules on infected leaves turn black during the fall.
Spores produced in the spring, summer and fall are spread by the wind, germinate on the leaves and infect new tissue. Extended periods of wetness will help the spores germinate and the disease will develop quickly. Low light, inadequate fertilization, drought and infrequent mowing encourage rust development.
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Photos and content generously provided by The Lawn Institute