Cause Erysipheviburni (formerly Microsphaerasparsa), a fungus that
becomes abundant in late summer, particularly on plants in shade. It is favored
by a combination of warm days, cool nights, and humid conditions, but is
inhibited by rain.
Symptoms The disease
primarily affects young leaves and shoots. Affected plant tissues develop a
powdery white growth of fungal mycelia. The fungus can be found on either leaf
surface. Tiny black specks may be observed among the white mycelia in late
summer. Developing leaves may be somewhat deformed by severe infections.
Powdery mildew can be controlled by
cultivar selection and sanitation. Since the fungus overwinters oninfected
canes, in buds or on old leaves, it is important toprune infected plant parts
and remove leaves before new growth starts in the spring. If you
plant susceptible varieties,ensure the location is sunny with good air
Pruning rose canes to ensure good
air circulation may alsohelp.
Fungicides may be required for
Fungicides active against powdery
mildew include folpet,lime sulphur, sulphur, triforine, thiophanate-methyl