| Aster Yellows | Plants are stunted with excessive branching and yellow, strap-shaped leaves. | Phytoplasma | Destroy infected plants. Maintain good insect and weed control in the greenhouse. |
| Botrytis Blight | Leaves, especially those near the soil surface, rot and become covered with gray fungal growth as do fading flowers. | Botrytis cinerea | Heat and ventilate to maintain low humidity. Remove dead and dying tissue from the greenhouse. Apply a fungicide. |
| Damping-off | Seedlings wilt and die. | Pythium spp. | Plant in pasteurized potting mix. Discard infected plants. Apply a fungicide. |
| Phytophthora Root Rot | Roots rot and plants wilt and die. | Phytophthora primulae | Plant in pasteurized potting mix. Discard infected plants. Apply a fungicide to protect healthy plants. |
| Rhizoctonia Crown Rot and Bud Blight | Roots and stems brown. Plants wilt and die. Older plants may fail to flower or produce new leaves. | Rhizoctonia solani | Plant in pasteurized potting mix. Discard infected plants. Apply a fungicide to protect healthy plants. |
| Thielaviopsis Root Rot | Small black spots form on roots. Gradually, the entire root system browns. Old leaves die while younger leaves yellow. | Thielaviopsis basicola | Plant in pasteurized potting mix. Discard infected plants. Apply a fungicide to protect healthy plants. |
| Viruses | Leaves may be mottled, yellowed, or have dead spots or be curled. Plants are stunted. Flower color may break. Entire plants may die. | Tobacco necrosis, primrose mosaic, cucumber mosaic, impatiens necrotic spot, tomato bushy stunt, alfalfa mosaic, or tobacco ringspot. | Discard infected plants. Maintain good insect control, especially aphids and thrips. |
