Why Does My Lisianthus Look Unhealthy?

Are there any small, round reddish brown spots with white to grey centers on the upper surface of the leaves?

Are the flowers covered with gray mold, leaves may be blotched or discolored?

Do the leaves have pale areas on upper surfaces and "downy" patches underneath?

Are there any yellow and wilting leaves, brown streaks appear on a lower surface of leaves, the growth is stunted?

Are the leaves mottled with dark green?

Are the leaves yellow and the plant looks weakened, tiny, white insects are present?

Are the leaves curled and distorted?

Are the leaves covered in coarse stippling and may appear silvery?

These symptoms indicate Alternaria leaf spot. Warm, wet conditions favor this fungal disease. Spray infected plants with copper and/or sulfur to prevent further disease development. Plant only pathogen-free seed from a reputable nursery.

Gray mold on flowers is probably caused by fungal disease - Botrytis blight. You can prevent Botrytis blight disease by planting in areas with good air circulation. Water plants sparsely. Severely infected plants should be removed. Spray weekly with a copper fungicide until the disease is under control.

Pale areas on upper surfaces of the leaves and "downy" patches underneath are caused by Downy mildew. This fungus spreads quickly during cool, wet nights and warm, humid days. Leaves will wilt and die. Remove and destroy all affected plant parts and encourage good air circulation around plants by thining them. Water plants early in the morning to make sure they dry before nightfall.

Fusarium wilt is a fungal disease that causes these symptoms in basil. High soil temperatures favor the disease emergence. Use only disease-free seed. Treat seeds with hot water to kill fungi before planting. Destroy affected plants at the first sign of fusarium. Rotate crops to nonsusceptible species.

Mottled or streaked leaves are caused by Mosaic Virus. There is no cure for infected plants. Remove and destroy all flowers that have the symptoms of the mosaic virus. Mosaic virus is spread by aphids, so the best way of preventing the disease is to control these insects.

Yellow leaves and stunted look are caused by whiteflies. These tiny, mothlike flies and their larvae feed by sucking plant juices. Whiteflies secrete honeydew, a sugary substance that makes leaves sticky to the touch. Control whiteflies by eliminating garden weeds and by introducing green lacewings in the garden. Spray infested plants with insecticidal soap every 3 days for 2 weeks.

Distorted and curled leaves are caused by aphids. These tiny insects cluster under leaves and on growing tips where they feed on plant sap. Leaves, stems, and buds get distorted and later leaves and flowers drop from the plant. You can control them by washing them off the plant with water spray. Insecticidal soap should be used with severe infestations.

These symptoms may indicate thrips. Thrips are tiny, yellow to black flying insects. Severely infected plant parts should be removed and destroyed. Control thrips by introducing lady beetles or lacewings, their natural predators. Insecticidal soap helps in severe infestations.

If there are tunnels in leaves the culprits are leafminers. These tiny fly larvae feed within the leaves in meandering mines that become wider as the larvae grow. Prune off and destroy all infested leaves. Remove debris in fall because it might contain overwintering leafminers. Introducing parasitic wasps is a very effective method of controlling leafminers.