Arborvitae Diseases
Gary W. Moorman, Professor of Plant Pathology
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| Branchlet | The oldest branchlets turn brown in autumn and fall off. | Normal browning. | Branchlets rather than scale leaves are shed in autumn as a normal part of the plant development. |
| Kabatina twig blight | Tips of one-year-old branches die and turn brown or ash gray. These remain on the shrub for many months. Larger branches can be invaded and girdled. On the dead tissue where it meets the still-living wood, small, black, pimple-like fungal fruiting structures form. Microscopic examination reveals oval, colorless spores. See Phomopsis below. | Kabatina thujae | Prune and destroy infected twigs and branches. Both Kabatina and Phomopsis twig blight can occur on the same plant. Apply mancozeb to protect the foliage. |
| Pestalotiopsis tip blight) | Twig tips turn tan to brown in color and have black, pimple-like fungal fruiting structures dotting their surface. | Pestalotiopsis funerea | Protect plants from winter injury, drought, and other stresses. Apply copper to protect foliage. |
| Phomopsis twig blight | Tips of branches die and turn brown or ash-gray. These remain on the shrub for many months. Larger branches can be invaded and girdled. On the dead tissue where it meets the still-living wood, small, black, pimple-like fungal fruiting structures form. Microscopic examination reveals both oval and long, thread-like colorless spores. See Kabatina above. | Phomopsis juniperovora | Prune and destroy infected twigs and branches. Both Kabatina and Phomopsis twig blight can occur on the same plant. Apply thiophanate methyl when new growth is present. |
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No. |
Risk Level |
Class | Active Ingredient |
REI | Trade Names (EPA reg #) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807), Systec 1998 (48234-12) |
| M | 1 |
Copper, complex |
copper sulfate | 12 | Camelot (1812-381), Phyton 27 (49538-3) |
| Copper, fixed | copper hydroxide | 48 | Kocide (352-656), Champion (55146-1) | ||
| Dithiocarbamate | mancozeb | 24 | Dithane (707-180), FORE (707-87), Pentathlon (1818-251) | ||
| manganese + zinc | 24 | Protect T/O (1001-65) |
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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