Pests on Butterfly Weeds

Spider Mites

• Spider mites are small red, brown, yellow or green insects that may be hard to spot on the butterfly weed unless you use a magnifying glass. Belonging to the Tetranychidae family, they're related to other pests such as spiders and ticks. If the leaves of the butterfly weed have light flecks, the plant may have spider mites sucking out the milky sap. You can control spider mites by planting companion plants, such as marigolds or sweet alyssum, that attract lady beetles, also called ladybugs, which will eat the spider mites. Insecticides such as Talstar, and horticultural oils such as Sunspray, also will help. Follow the manufacturer's directions for proper usage.

Oleander Aphids

• The oleander aphid, also known as the milkweed aphid, is a yellow and black insect ranging in size from 1.5 to 2.6 mm. This aphid damages the butterfly weed by ingesting the milky sap from the tender shoots, leaving a black mold on the plant that can result in the plant not growing as tall as it should. Control the oleander aphid by applying insecticidal soaps or horticultural oils, which, according to the University of Florida Extension, are quite effective. Follow the directions on the label for correct usage.

Whiteflies

• Whiteflies look like tiny moths covered with a white powderlike wax, and are sometimes found on the underside of the leaves of the butterfly weed. They suck out the milky sap, causing the plant to weaken and the leaves to turn yellow and drop off. Whiteflies also excrete sticky honeydew on the leaves, causing a black mold to form. To control whiteflies on the butterfly weed, you can plant flowers to attract lady beetles, which will eat the whiteflies. You can also apply an organic insecticide such as neem oil or an insecticide containing pyrethrin. Apply as soon as you notice the whiteflies. The University of Missouri Extension recommends 4 to 5 applications every 5 to 7 days. Follow the directions on the label for the amount to use per application.

Mealybugs

• Mealybugs range from 1 to 4 mm long. The females look like tiny pieces of oval cotton, and the males favor gnats with wings. Mealybugs eat the milky sap of the butterfly weed, causing yellow spots on its leaves. The mealybugs also excrete honeydew onto the leaves and stems, causing a sooty, black mold. This will affect the butterfly weed's growth process, and leaves may begin to drop. Spray insecticidal soap or oils directly onto the mealybugs when you first notice them. Look under leaves and on stems, where they may be hiding.