The bean is one of the oldest cultivated crops on the planet and some variation of the bean is found on every continent of the world with the exception of Antarctica. This ability to adapt well to any climate makes the bean a popular choice among home gardeners. Sadly, the bean is not only a favorite of humans; many insects enjoy munching on the stems, pods and leaves of the bean plant.
White to yellow in color, the seedcorn maggot feeds on the contents of the bean seed causing poor growth and spindly seedlings. The seedcorn maggot has no legs and is about a quarter inch when fully grown. The adult is brown-gray in color and looks like a small housefly. Seedcorn maggots lay eggs in the debris that surround the bean plants. Planting bean plants in warm soil helps plants outgrow maggot injury. Seedcorn maggots can't be controlled once they appear on plants. When planting crops in areas that were previously known to be infested with seedcorn maggots, a soil-applied insecticide will stop the seedcorn maggot from returning. Always follow manufacturers instructions when using insecticides.
Sometimes called black fly, the bean aphid feeds on bean plants by sucking sap from the stems and foliage. Damage is minimal until the population of aphids expands. Signs of aphids include curled leaves and yellowing plants. Bean aphids are about 1/12 inch long and have a soft body. Usually blue-black or dark green in color, aphids have wings and white appendages. They are known to transmit the bean common mosaic virus. Aphids are best controlled by natural predators and parasites. High populations of aphids can be reduced by using an insecticide that is made specifically for aphids. Use caution when spraying plants with insecticides and follow all of the manufacturers instructions.
Bean Leaf Beetles
The adult bean leaf beetle is oval-shaped, a quarter inch long and are yellow-green with four black spots and black markings along their wings. Younger plants are more susceptible to an attack by bean leaf beetles. Adult beetles eat the undersides of leaves, creating an eighth-inch hole in the leaf. Large groups beetles will eat the first leaves of a seedling and may eventually kill the young plant. It is possible to hand remove beetles from your beans if there aren't too many and if your garden is not large. Treat greater infestations of bean leaf beetles with insecticide. Always follow the manufacturers directions on the label.
Known for its shield shape, the stink bug will suck the sap from the buds, blossoms and seeds of the bean plant. Young pods become deformed if pierced before they have developed. Seeds will often be flat and shriveled. The green stink bug is marked with a yellow-orange line that borders the edges of the major body regions. Brown stink bugs are a yellow-gray in color. Leaf-footed stink bugs have brown bodies and a cream stripe on their back. Sizes of the stink bug range from an eighth inch to a half inch. The stink bug repels most predators by giving off a foul odor but a few species of birds will eat them. Insecticide is the best option for controlling the stink bug. Use the recommended solution for the bean plant and follow all directions on the label.