| Disease |
Symptoms |
Pathogen/Cause |
Management |
| Anthracnose |
Brown
spots up to 1/4 inch in diameter on leaves go
entirely through the leaf and have reddish-brown halos.
Tiny, dark-brown fungal fruiting structures appear as numerous
dots within the brown areas. Small, reddish-brown spots without
brown centers may pepper portions of the leaf or extend along
veins. Large, brown blotches of dead tissue may occur on leaf
tips, along the margin of leaves, or between
the veins. Leaves on branch tips may be completely blighted
and remain attached over the winter. Reddish-brown dead spots
occur on the flower
bracts. Lower twigs
and branches die. Small, raised, pimple-like fruiting structures
form on the dead twigs. Water sprouts form along the trunk of
severely affected trees. The entire tree may be killed over
a period of years. |
Discula destructiva |
Prune and destroy dead twigs and branches during
dormancy and when observed during the growing season. Protect
trees from drought stress, winter injury, and dogwood borer
attack. Rake and destroy fallen leaves. Apply azoxystrobin,
chlorothalonil, mancozeb, myclobutanil, propiconazole, or thiophanate
methyl + mancozeb during bud break to protect new flowers, twigs,
and foliage. Grow Cornus kousa
or C. kousa X C.
florida hybrids that have resistance to this
fungus. |
| Leaf and Flower Blight |
Irregular, brown, wrinkled patches form on flower
bracts and leaves in the spring. Gray mold grows on the dying
tissue if the weather remains very humid. |
Botrytis cinerea |
This disease only occurs if weather conditions
are very wet and humid in the spring. Warm, dry weather curtails
the disease. |
| Crown Canker |
Leaves are smaller than normal, light green,
and exhibit fall leaf coloration prematurely. Twigs and large
branches die as a canker forms at the base of the tree. The
canker slowly girdles the tree. During this time, the tree flowers
and fruits profusely. The tree eventually dies. |
Phytophthora cactorum |
Remove the infected tree and do not replace it
with another woody ornamental until the soil has been fumigated
and aerated. Apply mefenoxam or metalaxyl to nearby dogwoods
to protect them from invasion. |
| Decline |
Severe anthracnose (see above) occurs on leaves
and causes extensive twig and branch dieback. Water sprouts
form along the trunk as cankers girdle branches and the main
trunk. The lower limbs of the tree die first but eventually
the entire tree dies. |
Discula destructiva
plus stresses such as winter injury, drought, and attack
by dogwood borers. |
Do not plant native dogwoods (Cornus
florida) in locations prone to severe winter conditions
or drought. Protect trees from winter injury and irrigate to
prevent drought stress. Treat for anthracnose and borers. Grow
Cornus kousa or C.
kousa X C. florida
hybrids that have resistance to decline. |
| Powdery Mildew |
White
fungal growth develops on the surface of leaves late in
the spring and continues into the season. Sometimes this is
a very light growth and not easily observed from a distance.
Leaves become dull green and may redden. Premature defoliation
may occur. |
Microsphaera pulchra |
Infection occurs early in the season and may
weaken trees. Apply azoxystrobin, chlorothalonil, propiconazole,
myclobutanil, potassium bicarbonate, triflumizole, or triadimefon
as soon as mildew is observed. |
| Septoria Leaf Spot |
Angular gray to brown spots with yellow or dark
purple halos form on leaves. Spots can be up to 1/4 inch in
diameter. Small dark brown fruiting structures of the fungus
are visible within the brown spots. |
Septoria cornicola |
Apply chlorothalonil to protect new leaves during
bud break. |
| Spot Anthracnose |
Reddish-purple spots on flower bracts are up
to 1/10 inch in diameter. Leaf spots are circular to angular
dark purple areas less than 1/32 inch in diameter and often
drop out leaving shot holes. Spotting can occur on twigs and
fruit also. |
Elsinöe corni |
See anthracnose above. |
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}