Controlling the Hibiscus Sawflies

Kirsten S. Traynor
Frederick County Master Gardener Program

Your hibiscus is finally starting to take off, one of the later plants to get going in late spring. It is unfurling gorgeous green leaves that will bear beautiful, dinner plate-size blooms in just a few weeks.

On your afternoon stroll through the garden, you happen to notice little black bugs congregating on those large leaves. They resemble a small, black fly with a bright orange-brown thorax just behind the head. These pests, not quite a quarter-inch long, are using your hibiscus leaves as landing pads.

Although they look harmless enough sunning themselves in your garden, they are not a welcome garden bug. They are hibiscus sawflies, also known as mallow sawflies. Their scientific name is Atomacera decepta.

The hibiscus sawfly also attacks other garden favorites. Plants especially susceptible to attack include the ornamentals hollyhock (Alcea rosea), rose mallow (Hibiscus moscheutos) and some other hibiscus species.

This sawfly shows little or no interest in some other economically important malvaceous plants, including cotton, okra and rose of Sharon.

When you see the adult hibiscus sawflies congregating on the plant's leaves, you can be sure your plant has come under attack. Although hibiscus sawflies are considered a minor pest, they can wreak major havoc to prized hibiscus.

The females lay eggs in the upper surfaces of leaves, near the leaf margin, producing blister-like swellings. When these eggs hatch, the larvae move to the underside of the leaf and begin feeding.

Within a few short days, they will turn the leaves of the hibiscus into skeletonized remains that resemble delicate lacework.

This frenzied feeding usually occurs in late July, so you still have time to take action and stay vigilant. The most difficult problem for gardeners is that the young larvae of the hibiscus sawfly look like green caterpillars with black heads and tiny black raised bumps called spines. This leads them to conclude their flowers are under attack by a caterpillar instead of a sawfly, and so they treat incorrectly.

The University of Maryland, College of Natural Resources recommends the following control: Handpick larvae or prune out affected tissue and destroy. If the population is too big, or the plant is too tall to hand-pick, treat with Conserve.

Unfortunately, I took action too late last year and lost one of my dinner plate hibiscus plants. These little sawflies can do a lot of damage in a short time. They are relatively easy to control with foliar sprays, but because the hibiscus sawflies produce up to six generations in one season, the susceptible plants need to be sprayed on numerous occasions.

There is a glimmer of hope for beloved hibiscus plants. Studies are being done to breed for resistant plants that are less susceptible to the ravenous appetites of the sawfly. Three genotypes show promise in breeding for hibiscus with resistance to the hibiscus sawfly: H. acetosella, H aculeateus and H. grandiflora.

Let's hope resistant varieties make it into nurseries soon, because hibiscus and hollyhocks are too pretty to be lost from our gardens because of a pesky pest.

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