Erysiphepulchra (formerly Microsphaerapulchra)
is the fungus that attacks leaf surfaces and tender shoots and causes powdery
mildew. New growth is covered with a fine, white, powdery coating, typically on
the upper surfaces of the leaves. Infected leaves exhibit marginal leaf scorch,
dead patches, reddish discoloration, yellowing and premature defoliation.
Spores are spread by wind to surrounding dogwood plants.
COMMENTS on disease
Powdery mildew is most common in
dense, shady areas where the air circulation is poor. Warm, dry days and cool,
damp nights favor disease development.
powdery mildews of landscape trees occur late in the summer and are therefore
of little consequence. Infection that begins early in the season can be
devastating, and the use of fungicides may be warranted.
controls should be the first line of defense. Begin by raking up and destroying
all fallen leaves. Prune out dead and infected branches and twigs. Improve air
circulation and sunlight penetration around the tree by removing overhanging
branches and crowding vegetation. Resistant species and cultivars are available
and should be considered for new plantings. Cultivars of the oriental
dogwood Cornuskousa (such as `Milky Way`, `Milky Way Select`,
and `National`) and many of the Cornusflorida x Cornuskousa hybrids
(such as `Aurora`, `Constellation`, `Celestial`, and `Stellar Pink`) are
generally resistant to powdery mildew. The flowering dogwood (Cornusflorida)
cultivars `Appalachian Joy`, `Appalachian Blush `, `Appalachian Snow` and `Appalachian
Mist` are very resistant to powdery mildew. `Cherokee Brave`, `Springtime`, and
`Pygmy` have partial resistance. All other flowering dogwoods (C. florida)
are susceptible. Red-twig dogwood (C. sericea) is very susceptible to
If disease is severe enough to
warrant the use of fungicides, be sure that the dogwood is a valuable specimen
and the spray equipment can provide good coverage. For fungicides to be
effective, they must be applied as soon as symptoms are noticed. Very effective
fungicides for dogwood powdery mildew control include myclobutanil and
propiconazole. Some control can also be obtained with triadimefon, thiophanate
methyl, sulfur, or copper fungicides .