Milkweed plants are found mainly in the Americas, though they also grow in Europe, Africa and Australia. Ninety-five percent of the 3,000 species are tropical in origin. Milkweed plants are perennials and can be found as herbs, vines, shrubs or trees. The scientific name for the milkweed family is Asclepias. Milkweed gets its name from the milky substance that flows from damaged portions of plants.
You can identify common milkweed plants found in 40 U.S. states and portions of Canada by the 1 1/2-inch to 2-inch lance-shaped leaves. Look for the flowers to be bright orange with a diameter of 2 inches to 5 inches. Asclepias tuberosa is the common type found in North America. Its common name is butterfly weed because Monarch and Queen butterflies use this plant to lay eggs and feed upon.
Signs of damage are easy to find. Look for leaf skeletonization as a result of newly hatched caterpillars feeding on the lower leaf tissue. Look for holes and irregular cut patterns to develop in both leaves and flowers as the caterpillars mature. Holes along leaf margins and scars on leaves can be a sign of adult beetles. Plants may become completely defoliated depending on the number of larvae or beetle present.
The most common pest found on milkweed is the Monarch butterfly caterpillar. These butterflies lay eggs along the underside of host plants. The oleander aphid is the next common pest. According to the University of Florida, the aphid causes mainly aesthetic damage in the form of black mold and stunted plant growth. The milkweed beetle is another common pest.
Use of insecticides can be difficult due to the rapid reproduction rate of pests that feed on milkweed plants. Insects can also develop resistance to insecticides. Use a blast of warm water to clear the plant before applying chemicals. Avoid using chemicals when flowers are present to avoid affecting plant growth and beneficial bees that pollinate the plants.
Use biological controls to naturally control infestations on plants. Control aphids with lacewings or lady bugs. Use stink bugs to control caterpillar populations. Parasitic wasps can be used to control both aphids and caterpillars.