Asparagus beetles in home gardens

Jerry Vitalis

The warm temperatures and ample rain have helped gardeners enjoy a great asparagus harvest. The conditions have also made it easy for the asparagus beetles to thrive as they lay their eggs on nearby weeds as the host.
The common asparagus beetle and the spotted asparagus beetle are two of the main pests of asparagus. Both beetles have oval-shaped bodies with moderate length antennae. The common beetle adult is bluish-black with six cream-colored spots on its back, while adult spotted beetles are reddish-orange with twelve black spots. The spotted asparagus should not be confused with the beneficial lady beetles that have an oval, almost rounded body, with a varying number of spots. They also have heads that are partly to completely concealed when viewed from above and a short antennae.
Common asparagus beetle adults overwinter in sheltered areas such as under loose tree bark, hollow stems of asparagus plants and of course weeds. Adults appear in gardens just as the spears emerge from the soil in the spring. They lay many dark brown, oval-shaped eggs on end in rows on spears, ferns, flower buds, etc. The eggs hatch within a week and the larvae migrate to the ferns to start feeding. They feed for about two weeks and fall to the ground to pupate in the soil. About a week later, adults emerge to start another generation, feeding on the ferns for the rest of the growing season.
The spotted asparagus beetle has a similar life cycle, but usually appears in gardens later; appearing in mid-May and disappearing in late July. The orange larvae typically feed on the berries, or fruit of the asparagus, feeding on the spears by both varieties. They can cause browning, scarring, and may cause the spears to bend over into a shepherd’s crook. Significant defoliation can weaken the plants and reduce the ability to provide nutrients for the coming year, therefore causing winter kill, especially in young plants.
Handpicking can be effective in small gardens, but less practical in large gardens. If you detect heavy infestation, you may choses to use an insecticide. Look at the label and look for the active ingredients that have pyrethrins, malation, carbaryl, and permethrin. Since carbaryl kills honey bees, avoid spraying when other plants are flowering and spray towards evening. Always read the labels on insecticides and follow the instructions carefully.

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