Viburnum leaf beetle is a comparatively new pest to Chicagoland gardens. Right here’s methods to deal with an infestation.

“The leaves of my arrowwood viburnums appear like they’ve been shredded, and the small items of leaves that stay have turned utterly brown. This has not occurred in earlier years. I had at all times thought that this viburnum was trouble-free and straightforward to develop. What is that this drawback and what ought to I do?”

— Gail Westerman, Highwood

Your description seems like your viburnums have been attacked by the viburnum leaf beetle, a comparatively new insect pest for the Chicago area.

I’ve been seeing plenty of arrow wooden viburnums in residence gardens, with plenty of harm this 12 months, together with my very own vegetation, for the reason that arrowwood viburnum is a favourite of this insect. The Chicago Botanic Backyard screens its viburnum assortment for this pest annually now and treats it as wanted.

You have to to manage the insect in your viburnums, in addition to present supplemental water throughout dry durations this summer time if you wish to save them. The vegetation ought to leaf again out this 12 months in the event that they have been wholesome earlier than being broken.

The viburnum leaf beetle is a heavy feeder that may utterly defoliate viburnums. It occurred in a short time on the viburnums in my backyard. Each larvae and adults feed on the leaves and take away leaf tissue between the midrib and bigger veins. The leaves will then have a skeletonized look, which is able to appear like they’ve been shredded.

Crops might die after two or three years of injury from very heavy infestations. This insect’s feeding is restricted to viburnum species, so that you would not have to deal with different vegetation in your backyard. Monitor another viburnums that you’re rising, although, for this insect.

The viburnum leaf beetle prefers viburnums with clean leaves (little hair or pubescence). Arrowwood viburnum (Viburnum dentatum) and American cranberrybush viburnum (Viburnum trilobum) are generally planted viburnums which can be most popular hosts and can doubtless be killed over a course of two to a few years if no management therapies are made.

Different extensively planted viburnums comparable to burkwood viburnum (Viburnum burkwoodii), blackhaw viburnum (Viburnum prunifolium) and aromatic snowball viburnum (Viburnum carlcephalum) have various levels of susceptibility to break however typically usually are not destroyed. Koreanspice viburnum (Viburnum carlessii), Judd viburnum (Viburnum juddii) and doublefile viburnum (Viburnum plicatum) are typically immune to feeding. There typically will likely be extra harm on any viburnums which can be grown within the shade.

Viburnum leaf beetles overwinter as eggs on twigs of the host plant. In Might, larvae hatch from the overwintered eggs and start feeding on the host vegetation — that is the harm you might have not too long ago seen in your vegetation.

The larvae are greenish-yellow and develop darkish spots as they age. They’re normally discovered feeding in teams on the leaves. The larvae drop to the bottom and pupate between early and mid-June and stay within the floor for about 10 days earlier than rising as adults in mid- to late July, so chances are you’ll not see them presently.

The grownup beetle is small, ½ to ⅜ of an inch lengthy and is a golden-brown shade with sheen when within the daylight. Adults will stay energetic till the primary frost. Growth from egg to grownup takes eight to 10 weeks.

In late summer time and fall, females will start laying eggs. They chew holes within the bark of twigs to deposit eggs after which cowl them with excrement and fragments of chewed bark. A feminine can lay as much as 500 eggs.

One efficient option to management viburnum leaf beetle is to prune and destroy infested twigs after egg laying has ceased within the fall in October, up till April. However pruning alone is not going to be sufficient. You have to to spray an insecticide comparable to spinosad, acephate, carbaryl or malathion when larvae first seem in early Might for good management. Acephate can have a level of residual exercise, as it would transfer into the leaves.

A second utility in mid- to late summer time on feeding adults could also be useful if harm is extreme, however a technique of simply treating adults is not going to present efficient management. It’s best to solely spray your viburnums in case you discover this insect and comply with all instructions for correct and protected use of the product that you’re utilizing. Present supplemental water to the affected viburnums throughout any dry durations for the remainder of this 12 months to assist scale back stress on the vegetation.

For extra plant recommendation, contact the Plant Info Service on the Chicago Botanic Backyard at [email protected]. Tim Johnson is senior director of horticulture on the Chicago Botanic Backyard.