| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Bacterial soft rot (Dickeya (=Erwinia) chrysanthemi) |
Soft, watery rot of leaves; often foul smelling. Starts as small water-soaked area. Infection is through wounds. Often kills cattleya plants. | In soil and decaying plant debris. Bacteria spread in water. Favored by warm, moist conditions. | Avoid overhead watering, wounding plants, and provide horizontal air movement and good aeration. Observe strict sanitation. Disinfect knives between cuts. |
| Black rot and seedling damping-off (Pythium ultimum *, Phytophthora cactorum *) |
Starts as small, water-soaked leaf spots and root rot. Decay may progress rapidly. Affected tissues turn black and are sometimes soft. | Soilborne fungi. Spores spread in water. Favored by warm moist conditions (above 65°F). | Drench plants with oomycete (water mold) specific fungicide. Steam or chemically treat growing media and used pots. Remove badly infected plants. |
| Botrytis flower brown speck or rot (Botrytis cinerea) |
Tiny, light-brown spots on blossoms may enlarge to rot entire flower. Fuzzy gray fungal spores develop on flowers if kept moist. | On plant debris. Spores airborne. Favored by cool, moist conditions. | Eliminate old flowers. Eliminate plant debris, both inside and outside growing area. Avoid getting flowers wet. Treat with fenhexamid. |
| Gloeosporium leaf spot (Gloeosporium spp.) |
Prominent, sunken, reddish brown spots with definite margins. Spots may coalesce and kill entire leaf. Spots start as minute, dark areas, often at leaf tips. | In infected plants. Spores spread in water. Favored by moist conditions and unfavorable growing conditions. | Provide better growing conditions. Avoid wetting foliage. Remove infected tissues. |
| Rust (Sphenospora kevorkianii, Uredo nigropuncta) |
Pustules of powdery, yellow or orange spores on undersides of leaves. | In infected plants. Spores airborne. Moisture needed for only short period. Not too common. | Avoid wetting leaves. Destroy infected leaves. |
| Virus or viruslike disease | Symptoms | Natural spread and host range | Comments on control |
| Blossom necrotic streak (a strain of Cymbidium mosaic virus) |
Blossoms open without evidence of brown spots or streaks, which become visible after about 1 week or longer. Long, yellowish, irregular streaks may develop on leaves. | Can be spread on cutting tools. | Use clean cutting tools. Destroy infected plants. |
| Leaf necrosis (Cymbidium mosaic virus) |
Irregular, elongated streaks of dead tissue on undersurface of older leaves. Some leaves may be killed or various patterns of sunken, black tissue may develop. Infected plants may show no symptoms. | Spread by pruning tools. Cattleya and its hybrids, Cymbidium, Epidendrum, Zygopetalum, Angraceum, Laelia, Oncidium, Spathoglottis. | Use clean and disinfected cutting tools |
| Mild flower break (Odontoglossum ringspot virus) |
Flowers less variegated than above and without distortion. Leaves show only mild, hard-to-detect mosaic symptoms. Spots and streaks of increased pigment intensity. | Unknown, but can be transmitted by juice inoculations. Cattleya and its hybrids, Cymbidium, Odontoglossum, Phalaenopsis. | Isolate or destroy infected plants. Disinfect tools between cuts with a quaternary ammonium disinfectant. |
| Severe flower break | Variegation of flower color. May also distort sepals and petals. Leaves mottled with streaks of light and dark green tissue. Dark green areas somewhat raised, producing ridges and bumps. | Spread by green peach aphid. Cattleya and its hybrids, Cymbidium. | Same control for all viruses. |
| Symmetrical flower break | A symmetrical variegation in which pigment occurs along sepal margins and over most of petals, except in middle areas that have little or no pigment. Leaves may develop an inconspicuous mosaic mottle. | Unknown, but can be transmitted by juice inoculations. Cattleya. | Use clean and disinfected cutting tools |
| * For additional information, see section on Key Diseases. |