HOSTS: Iris.
DESCRIPTION: Mycosphaerella
macrospora develop
as tiny brown spots which later turn yellow and then run
together. When infection is severe leaves may die. Iris leaf spot is a
common disease caused by the fungus Mycosphaerella
macrospora (formerly Didymellina macrospora). Wet
weather or excessive overhead irrigation creates severe
outbreaks of this disease
LIFE
CYCLE: Mycosphaerella
macrospora overwinters on dead leaves and other plant materials. Spores are
formed in the spring and are dispersed by wind and rain. They infect
leaves directly or through stomata. During wet warm weather the
disease cycle may occur many times. Acid soil may intensify the
disease.
Premature killing of the leaves can weaken the bulb
or rhizome causing the gradual death of the entire plant. Although
infection is usually confined to the leaves, stems, flower stalks, and
buds may become infected during severe outbreaks of this disease.
CONTROLS:
- Remove and destroy dead and infected leaves when they begin to die after Iris has flowered.
- Plant irises in full sun.
- Maintain proper plant spacing to provide good air circulation.
- Rotate plantings.
- Check pH; maintain soil pH
above 6. Low pH encourages this disease.
- Apply sulfur if
infection is severe.; Apply when leaves are
6-8" tall, weather is wet and temperatures >65ºF.
