Spots on New Guinea Impatiens

Impatiens Necrotic Spot Virus

• Impatiens necrotic spot virus begins in the greenhouse where thrips spread it from plant to plant. It causes round, yellow or brown spots on leaves as well as browning veins, yellow line markings and discolored stems. The leaves may be distorted. Gardeners often bring the disease home on greenhouse-grown plants, so inspect new plants carefully before purchasing them. There is no cure, so destroy infected plants.

Botrytis Blight

• Botrytis blight causes abnormal leaves and flowers with purple to brown spots. The fungus that causes the disease overwinters in plant litter on the ground. In spring, it forms spores that spread on the wind or in splashing water. Keep the garden free of debris and avoid high-nitrogen fertilizers. Space the plants appropriately and keep them dry as much as possible by watering the soil, not the plants. Fungicides applied every 10 days may help prevent the disease.

Mites

• Both cyclamen mites and two-spotted spider mites cause flecks and spots on New Guinea impatiens. The spots indicate that mites are feeding on the undersides of the leaves. Cyclamen mites may congregate around the buds. These pests are very tiny and difficult to see, and damaged leaves may be the first indication of infestation. Use a contact insecticide labeled for use against mites. Spray the undersides of leaves thoroughly using three applications, five days apart. Mites develop resistance to insecticides and you may have to try products with different active ingredients to achieve control. Isolate infested indoor plants to prevent spread.

Western Flower Thrips

• Like mites, thrips are tiny insects that are difficult to detect until the damage is done. They like to feed on enclosed plant tissue such as buds, leaving black dots of feces as well as tiny spots on leaves and petals. Although the damage may be minimal, it is important to control thrips because they carry the impatien necrotic spot virus. Isolate infested indoor plants and use an insecticide labeled for use against thrips. Severe infestations are difficult to control and you may have to destroy the plant.