of Rhode Island GreenShare Factsheets
native flowering dogwood, Cornus florida, is frequently beseiged
with dogwood anthracnose and powdery mildew. Both of these fungi
can sometimes be controlled with multiple and well-timed fungicides
on otherwise unstressed trees. Frequent fungicide, water and fertilizer
applications, however, are laborious, expensive and represent potential
hazards to the environment.
reduce resource inputs and promote sustainability in the landscape,
we recommend planting one of the dogwood species or cultivars that
is resistant to these diseases. The dogwood species currently most
resistant to anthracnose and powdery mildew is Cornus kousa,
the kousa, or Korean, flowering dogwood. The kousa dogwood flowers
a bit later than C. florida, but otherwise fits the same
niche in the landscape as C. florida. The kousa dogwood offers
showy (mostly white but some pink) flower colors and a beautiful
scarlet to purple fall leaf color. The red and edible fruits, borne
on long pendulous stalks, and the mottled, exfoliating bark, are
additional attractions of the kousa. Although the species is generally
anthracnose-resistant regardless of cultivar, there a few susceptible
cultivars to avoid: C. k. 'Autumn Rose,' C.k. 'Moonbeam'
and C.k. 'Wolf Eyes.'
to combine the ornamental characteristics of C. florida with
the resistance traits of the kousa dogwood have led to several florida/kousa
hybrids. Resistance studies of florida/kousa hybrids are still continuing,
and results seem quite dependent on microclimate (particularly light
and humidity). However, the best indications at this time give us
four hybrids that are relatively resistant to anthracnose: C.
x. 'Auruora,' C.x. 'Celestial,' C.x. 'Stardust'
and C.x. 'Stellar Pink.' With the exception of 'Stardust,'
these hybrids are also resistant to powdery mildew. Beautiful in
flower, intermediate in timing between their C. kousa and
C. florida parents, these hybrids are sterile and do not
University of Rhode Island is working closely with nurseries to
increase the availability of these resistant cultivars,--in the
meantime, they can all be obtained from Shadow Nursery in Tennessee,
with the exception of 'Stardust.' 'Aurora' is known for its extremely
dense flowering that at is peak almost completely hides the foliage.
'Celestial' has sparkling white flowers that form a deep cup at
first and a more erect habit with uniform spread. 'Stellar Pink'
is known for its pale pink flowers with deeper pink veining and
its wide, rounded habit.
The resistance among cultivars of C. florida are dependent
on microclimate. Some research indicated that C.f. 'Cherokee
Red' and C.f. 'Cherokee Sunset' are resistant to anthracnose
('Cherokee Sunset,' however, is susceptible to a less fatal "spot
anthracnose"). Note that resistance to anthracnose does not hold
for the entire 'Cherokee' series. 'Cherokee Chief,' in particular,
is very susceptible to anthracnose. At least one new anthracnose-resistant
C. florida cultivar is being bred and tested; look for it in
the next couple of years, possibly by the name 'Presidential.'
closely related Cornus species that are considered resistant
to anthracnose, try C. alternifolia, C. officinalis
and C. mas. However, be aware that these species do not have
the same ornamental or ecological landscape use as Cornus florida.
If you opt to stick with C. florida, here's how to recognize
the common diseases, as well as practical cultural techniques that
will help to reduce disease incidence. Careful site selection and
plant management are crucial to achieving success with a species
or cultivar that is not genetically resistant.
is a fungal pathogen that forms purple or tan blotches on the leaves
and causes significant leaf and twig dieback. The entire tree can
be killed within two or three years after the first signs of infection.
Powdery mildew is another leaf fungus, indicated by white, powdery
blotches on the plant. Powdery mildew can cause stunted or distorted
growth and will decrease the aesthetic value of the tree--but because
it occurs later in the growing season, it will rarely cause tree
death. Both of these fungi thrive in cool, humid areas with poor
ventilation. See GreenShare Factsheets on Powdery
Mildew and Powdery Mildew
on Shrubs for more information.
is a critical factor in avoiding dogwood anthracnose. Traditional
recommendations have been to plant C. florida in partial
shade. However, for plants highly susceptible to anthracnose, you
might try planting in full sun, where ventilation is better and
cool moisture does not linger long. Avoid using mulches such as
leaves or partially decomposed compost, as both are likely to harbor
diseases. Prune out dead wood and suckers on a regular basis. Water
in the morning, only when necessary to avoid drought and avoid
foliage. Do not transplant trees from the "wild;" they are more
likely to already be infected with anthracnose.
avoid anthracnose in nursery situations, consider switching to drip
irrigation rather than overhead sprinklers, and try spacing container
stock significantly apart from each other. Field-grown dogwoods
often seem to have less trouble with anthracnose.
Renee Stoops, Plant Sciences Department, URI
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program