Why Does My Mandevilla Look Sickly?

Do the leaves and vines have white, cottony clusters on them?

Are the leaves yellow and covered with small bumps?

Are the leaves yellow and the plant looks weakened?

Are the leaves discolored, foliage may be webbed?

Are the buds and leaves covered with gray mold, stems are soft, may be rotted?

Do the stems have swollen, tumor-like growths on them?

Are there brown to black spots or blotches present on the leaves?

Does the plant wilts and leaves and stems are discolored?

White, cottony clusters on leaves and vines are caused by mealybugs. These tiny insects are covered with a fluffy white coating. They feed by sucking plants sap. They produce sticky substance honeydew which makes leaves sticky. You can control them by washing them off the plant with water spray. Insecticidal soap should be used with severe infestations.

Yellow leaves covered by small bumps are caused by scales. These tiny, shelled insects often feed on the undersides of the leaves, causing an unhealthy appearance with yellowish blotches on the upper leaf surfaces. Scrape off minor infestations with your fingernail. Prune out badly infested growth, or use a soft brush and soapy water to gently scrub the scales off the stems. Control scales by spraying insecticidal oil during the growing season.

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.

Spider mites are known to cause problems for Mandevilla. You can control spider mites by spraying plants thoroughly with water 2-3 times a day for several days. For severe infestations, spray plants with insecticidal soap or pyrethrin.

Gray mold on flowers and leaves, followed by rotted stems are symptoms that indicate a fungal disease - Botrytis blight. Other symptoms include brown to black spots that may appear on leaves and petals. You can only prevent Botrytis blight disease by planting flowers in areas with good air circulation. Water plants sparsely. Infected plants should be removed. Spray weekly with a copper fungicide until the disease is under control.

Bacterial disease Crown gall causes wartlike swellings on stems of Mandevilla. Gall bacteria are introduced into plants that are vulnerable due to wounds. If the plant is only slightly infected, prune off diseased growth. Destroy severely infected plants and avoid replanting Mandevilla or any susceptible plant species in the same spot.

Leaf spot diseases in Mandevilla are caused by several fungi that thrive on moist leaf surfaces. Brown to black spots develops on the leaves of infected plants. These spots often come together to form larger patches of dead tissue. Pick off and discard infected leaves, and spray the vine foliage every seven to ten days with sulfur. Avoid wetting the foliage while watering the vines. Mulching around plants helps prevent fungi from being splashed up from the ground by rain.

These symptoms are most likely caused by Fusarium wilt. There is no cure for Fusarium wilt, so the infected plants should be destroyed. Do not plant new vines or any susceptible plants to Fusarium wilt in the same spot for several years.

Southern wilt or southern blight is a less common, but devastating bacterial disease that may originate in greenhouses. Symptoms include yellowing and browning of lower leaves followed by leaf drop as the disease moves up the plant’s stem. If you suspect southern wilt, destroy the plant to protect your landscape from potential infection.