Mandevilla is a genus that incorporates about 100 species of tropical ornamental vines. These plants are prized for showy, fragrant flowers, rapid and climbing growth, and the versatility that allows them to thrive in the ground, in containers or even in hanging baskets. Although mandevillas have relatively few pest problems, they are still susceptible to a handful of pests, especially mealybugs and for some varieties, spider mites.
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Mealybugs are soft-bodied insects less than 1/4 inch long that are covered by a wax, white secretion. These pests use piercing mouthparts to feed on stem and leaf axils. Most mealybugs lay eggs, often in sacs, that hatch into "crawlers" before maturing into adults. Mealybugs cause leaves to turn yellow and drop and may distort new growth. Feeding mealybugs also excrete a stick, sweet substance known as honeydew that attracts unsightly sooty mold. Mealybugs may prove difficult to control, but they are susceptible to insecticides during the crawler stage. Ladybird beetles are natural predators of mealybugs, so preserve their population by reducing the use of broad-spectrum pesticides.
Mandevilla may be affected by some species of scales. These are unusual-looking, generally immobile and wingless insects that appear as bumps on the stem or leaves, where they use strawlike moutparts to feed on plant fluids. These pests, which also excrete honeydew, can, in large numbers, cause leaves to wilt, turn yellow and drop. A heavy scale infestation will also impact plant vigor. Scales are often controlled by natural predators, but ants, which feed on the honeydew, may protect the scale population and require control. Applications of horticultural oil applied when scales are in their active crawler stage should provide some degree of control. Also, remove heavily infested leaves or plant portions.
Whiteflies such as the giant whitefly (Aleurodicus dugesii) feed on fluids in the mandevilla. A large whitefly population will cause leaf loss, reduce plant vigor and excrete honeydew. Control whiteflies by removing and destroying heavily infested leaves or blasting a strong spray of water on infested leaves. Natural predators like green lacewings, lady beetles and parasitic wasps often provide ample control.
M. laxa, the white, fragrant variety of mandevilla and M. x amabilis "Alice Dupont" are especially susceptible to spider mite infestations. The red spider mite is generally the most common mite pest on mandevilla. Mites feed on leaves, first giving the leaves a stippled appearance, followed by a more severe discoloration and premature drop. This eight-legged pest which prefers hot and dry conditions, is often controlled by natural predators, so limit the use of broad-spectrum insecticides. Control this pest by removing heavily infested leaves, knocking pests and webbing off with a strong blast of water and, if necessary, with applications of horticultural oil, insecticidal soap or certain miticides.
Mandevillas may be plagued by aphids, which are tiny, soft-bodied insects. These pests use sucking mouthparts to feed on plant sap, causing leaf distortion and excreting honeydew, which hosts black sooty mold. Aphids, which are often difficult to control because of their high reproductive rates can be addressed with occasional strong blasts of water to knock them off the plants. These pests also have several natural enemies like green lacewings, lady beetles and parasitic wasps that are present if no broad-spectrum pesticide has impacted their health.