Hydrangea Diseases
Gary W. Moorman, Professor of Plant Pathology
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| BOTRYTIS BLIGHT | Petals turn brown and fall. Leaf spots form, especially where faded petals have fallen. Flower buds are killed before opening. | Botrytis cinerea | Space plants to insure good air circulation. Maintain low humidity. Avoid watering late in the day. Remove crop debris. Apply chlorothalonil, iprodione, mancozeb, or vinclozolin. |
| CERCOSPORA LEAF SPOT | Tan spots with reddish-brown halos develop on leaves. | Cercospora | Protect foliage with mancozeb, copper, or chlorothalonil. Water in a manner that keeps moisture off the leaves. |
| POWDERY MILDEW | Yellow areas form on leaves. These may become purplish. White, cottony fungal growth forms on the lower surface of the leaf. | Erysiphe polygoni | Apply triadimefon, piperalin, thiophanate methyl or fenarimol to protect leaves. |
| VIRESCENCE | Flowers are green and may be stunted. Leafy shoots grow from the flower parts. Plants decline and die. | Phytoplasma | Discard infected plants. Maintain good insect control. |
| VIRUSES | Leaves may be mottled, have yellow spotting, dead flecks, line or ringspot patterns. Plants may be distorted or have flower color breaking, or few flowers. | Hydrangea ringspot, tomato ringspot, impatiens necrotic spot | Plant virus-indexed cuttings. Maintain good insect and mite control. Destroy infected plants. |
Cercospora leaf spot.
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No. | Risk Level | Class | Active ingredient | REI Restricted Entry Interval | Trade names (EPA Reg. No.) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807), Systec 1998 (48234-12) |
| 2 | 3 | Dicarboximide | iprodione | 12 | Chipco 26GT (100-1138), Chipco 26019 (264-481), Iprodione (51036-361), Sextant (51036-361-59807) |
| vinclozolin | 12 | Curalan (7969-62-58185 | |||
| 5 | Piperidine | piperalin | 24 | Pipron (67690-1) | |
| M | 1 | Chloronitrile | chlorothalonil | 48 | Daconil (50534-9), Exotherm Termil (70-223) |
| 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) |
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).
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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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