Brown spots up to 1/4-inch in diameter go entirely through the leaf and have reddish-brown halos. Tiny, dark-brown fungal fruiting structures dot the brown areas. Small, reddish-brown spots without brown centers may pepper portions of the leaf or extend along veins. Also, 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.
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 a fungicide during bud break to protect new flowers, twigs, and foliage. Kousa dogwood (C. kousa) and hybrids of kousa and native dogwood (C. florida) are resistant to anthracnose and decline and should be used to replace dying trees.
Leaf and flower blight
Irregular, brown, wrinkled patches form on flower bracts and leaves in the spring. Patches of gray mold grow on the patches if the weather remains very humid.
This disease occurs only if weather conditions are very wet and humid in the spring. Warm, dry weather will curtail the disease.
Leaves are smaller than normal, light green, and exhibit premature fall leaf coloration. 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 but eventually dies.
Remove the infected tree and do not replace it with another woody ornamental until the soil has been fumigated and aerated. Apply a fungicide to protect plants.
White fungal growth develops on the surface of leaves late in the summer and during the autumn.
Erysiphe pulchra and Phyllactinia guttata
Apply a fungicide as soon as symptoms are seen. Cornus kousa, C. sericea, C. mas, C. alternifolia, C. alba, and C. controversa are much more resistant than most varieties of Cornus florida. The following C. florida cultivars are resistant: Jean's Appalachian Snow, Kay's Appalachian Mist, Karen's Appalachian Blush, and Appalachian Joy.
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.
Apply a fungicide to protect new leaves during bud break.
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.
See anthracnose above.