The first symptom of black leg is brown, water-soaked tissue at the base of the cutting. This turns shiny black and can quickly spread 3 or 4 inches up the cutting stem. Eventually the tops of affected cuttings and plants wilt, yellow and die. Fungus gnat larvae are often found in infected cuttings.
Peony anthracnose is caused by the fungus Gloeosporium. Symptoms seen in these photos include leaf spots, dieback, and dark lesions that may girdle stems.
Masses of salmon-colored spores may be observed in leaf spots and lesions. Buds and flowers may also be affected.
Prevent peony anthracnose by improving air circulation.
Avoid overhead watering. Remove and destroy all infected plant parts.
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2017-2018 New England Greenhouse Floriculture Guide
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Pythium species cause damping-off, root rot, crown and stem rot of all plant species. The roots of these snapdragon transplants are infected with Pythium root rot resulting in stunted and wilted plants. Pythium is favored by high fertility and high moisture; avoid overwatering and overfertilizing. Pythium is a natural inhabitant of the soil and can survive there indefinitely as well as in dirt and debris in the greenhouse.
Here are some management tips especially important for periods of cloudy, rainy weather:
Clean Plants: Keep plants in retail areas clean. Remove dead and injured plants and spent flowers a couple times a day even during the busy season. Botrytis and high ethylene concentrations from decaying plant tissue will cause premature loss of foliage and flowers.
Anthracnose (Colletotrichum sp) was recently diagnosed on mandevilla. Anthracnose is common on many ornamental plants. The primary symptoms are leaf spots, leaf blights and dieback. Infected leaves develop tan to brown spots or lesions that are typically associated with leaf veins. In severe cases leaf drop may occur. Because anthracnose symptoms take on different forms and appearances it can be mistaken with other fungal diseases. Submit suspicious plants to a diagnostic laboratory for proper identification.
Anthracnose (Colletotrichum sp) is common on many ornamental plants including mandevilla. Disease symptoms are leaf spots and dieback as seen in these photos. Infected leaves develop tan to brown spots or lesions that are typically associated with leaf veins. In severe cases leaf drop may occur. Because anthracnose symptoms take on different forms and appearances it can easily be mistaken with other fungal diseases. It is therefore beneficial to submit samples to a diagnostic laboratory for proper identification.
Tobacco mosaic virus (TMV) has a wide host range but is of special concern on solanaceous plants. Symptoms include yellow and green mottling, upward curling, necrotic leaf spots, leaf distortion, and overall stunting. Symptoms on plants in this photo are very subtle and could be mistaken for nutrient deficiency such as iron.
TMV is not transmitted by insects, but is transmitted mechanically in sap, by contact with contaminated equipment, by vegetative propagation, and it can be carried in seed. Once a plant is infected with a virus, it cannot be cured.
Damping off can be caused by species of Pythium, Phytophthora, Rhizoctonia or Fusarium. A laboratory diagnosis is required to determine the exact cause of damping off of seedlings and cuttings.
Symptoms of seedlings affected by damping-off generally rot at ground level and topple over. In this photo, note the stem canker at ground level.
Cloudy, rainy weather, cool nights and greenhouses full of plants provide an ideal environment for Botrytis. Botrytis symptoms may include leaf spots, flower blights, bud rots, stem cankers, and stem and crown rots and can be mistaken for other causes.