Dogwood Diseases
Gary W. Moorman, Professor of Plant Pathology
|
Disease |
Symptoms |
Pathogen/Cause |
Management |
|---|---|---|---|
|
Anthracnose and Decline |
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. |
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 propiconazole, azoxystrobin, myclobutanil, thiophanate methyl + mancozeb, chlorothalonil, or mancozeb, or 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. |
Botrytis cinerea |
This disease occurs only if weather conditions are very wet and humid in the spring. Warm, dry weather will curtail the disease. |
|
Crown canker |
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. |
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 to nearby dogwoods to protect them from invasion. |
|
Powdery mildew |
White fungal growth develops on the surface of leaves late in the summer and during the autumn. |
Erysiphe pulchra and Phyllactinia guttata |
Apply azoxystrobin, myclobutanil, chlorothalonil, potassium bicarbonate, polyoxin, or triadimefon as soon as symptoms are seen. Cornus kousa, C. sericea, C. mas, C. alternifolia, C. alba, and C. controversa are much more resistant than 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. |
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. |
Anthracnose
Anthracnose
Anthracnose on bracts
Anthracnose on underside of leaf.
Anthracnose on twig
Anthracnose twig dieback
Gray mold (Botrytis) on bracts
Powdery mildew
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No |
Risk Level |
Class | Active Ingredient |
REI | Trade Names (EPA Reg No) |
|---|---|---|---|---|---|
| 3 | 2 | Triazole | propiconazole | 24 | Banner MAXX (100-741), Propiconazole (51036-403), Spectator (62719-346-10404), Kestrel (66222-41-81943) |
| triadimefon | 12 | Strike (3125-436), Bayleton (432-1360) | |||
| myclobutanil | 24 | Systhane (707-253) | |||
| 4 | 3 | Acylanine | mefenoxam | 0 | Subdue MAXX (100-796) |
| 11 | 3 | Strobilurin | azoxystrobin | 4 | Heritage (10182-408) |
| 19 | 3 | Polyoxin | polyoxin | 4 | Veranda (66330-56-459807), Endorse (66330-41-1001) |
| M | 1 | Chloronitrile | chlorothalonil | 48 | Daconil (50534-9) |
| 12 | Echo (60063-7), PathGuard (60063-7-499), Concorde (72167-24-1812), Pegasus (72167-24-1812) | ||||
| Dithiocarbamate | mancozeb | 24 | Dithane (707-180), FORE (707-87), Pentathlon (1818-251) | ||
| manganese + zinc | 24 | Protect T/O (1001-65) | |||
| NC | 1 | potassium bicarbonate | 4 | Armicarb (5905-541-AA), Milstop (70870-1-68539), Kaligreen (70231-1), Remedy (62719-70), Agricure
(70870-1-1001)
|
|
| 1 + M |
1 | thiophanate methy + mancozeb | Zyban (58185-31) |
REI=Restricted Entry Interval
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic fungicides, are said to be 'at risk' to the development of resistance if they are used repeatedly. See the Risk Level in the above table (1 = low risk; 3 = high risk). The Fungicide Resistance Action Committee has developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action (See http://www.frac.info/frac/index.htm ). It is recommended that chemicals at high risk be used sparingly and in rotation or mixed with chemicals with different modes of actions (different FRAC number).
DISCLAIMER
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
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