Viburnum Under Siege. Part Two

Editor’s note: this is part two of this series. Don’t miss part one of Viburnum Under Siege.

The accidentally introduced pest, viburnum leaf beetle (Pyrrhalta viburni) or VLB for short, can destroy a shrub in just a couple of years. Unfortunately it continues to spread through North America. So I am trying to learn more about it, hoping that we can protect the viburnums in our area. This is the information that I have gathered from the sites listed and from my own observations. It doesn’t look very encouraging.

VLB larvae and leaf damage

© Beatriz Moisset

The grubs or larvae emerge from eggs early in the spring. They are yellowish or greenish, with black markings and can reach one third or a quarter of an inch in length.

They spend a few weeks feeding on the leaves by making numerous little holes between the veins. These holes are easy to identify. By early or mid June they climb down along the stems and bury themselves in the ground to pupate. When I searched for them in mid June, I found none, only the damage remained.

Viburnum Under Siege

Leaf damage inflicted on arrowwood

by the viburnum leaf beetle

© Beatriz Moisset

 The shoots of Viburnum dentatum are thin, strong and straight. Native Americans used them for arrow shafts. That is why this shrub is often called arrowwood. Until recently it was considered as a plant free from serious pests. Now, the arrowwoods in my area are under attack by an invasive leaf beetle.

Last May (2010), I began noticing leaves full of holes (skeletonized); something that I have never seen before. I finally spotted the culprits, little bugs hiding on the underside of damaged leaves. They look somewhat like caterpillars, but not quite; they are greenish, with black dots. A visit to the Bugguide site helped me identify them and provided links to several university sites full of information (see below). They are the larvae of the viburnum leaf beetle (VLB for short, Pyrrhalta viburni), an introduced pest from The Old World. Both the larvae and adults of this beetle feed exclusively on a variety of species of viburnum.

Viburnum leaf beetle larva and leaf damage

© Beatriz Moisset

Pollinators and the Garden in Winter

Man-made bee houses

Good replacement for holes in old logs

©Beatriz Moisset

Do you ask yourself: where do pollinators go in winter? We see them through the warm seasons visiting flowers and doing their invaluable job. But, then what happens to them? Putting aside the few, such as hummingbirds and monarch butterflies, which fly to better climates, all the others find a secluded place to spend the cold months. Like hibernating bears, many fatten themselves by stocking up on supplies and then go to sleep. Others rest as eggs or in an immature state such as a larva or pupa. Either way, they need a sheltered space safe from predators, parasites and excessive cold.

I know that some gardeners, with the best of intentions, destroy these vital shelters. It may be a good idea to take a look at all the places used by pollinators during the winter. This is one case in which a little untidiness may be a good thing.

Winter Food for Birds

Field of Canada goldenrod. © Beatriz Moisset

 When the days get shorter and other signs of winter hang in the air, most birds pack their bags and leave for warmer climates. They are not necessarily running away from the cold weather, but from the lack of their favorite food, insects.

Not all leave; the ones that can make it through the winter on nuts and berries stay. Also those who know where to find insects stay. Woodpeckers belong to this latter category. Some, such as hawks and owls, who feed on other birds, mice and other small creatures, also stay.

Biocontrols. Fighting Fire with Fire

Mile-a-minute choking trees
© Beatriz Moisset

 What to do when an introduced species, be it a plant or insect, gets so out of control that eradication seems impossible? This is a serious consideration. We see it happens again and again. Many species are so entrenched that all efforts seem futile, from the most ecologically benign, such as physically removing the offenders, to the least desirable ones, the use of pesticides.

Part of the reason why some introduced organisms become invasive is that they left behind the enemies that kept them in check in their native lands. Once free from such restraints they can become enormously successful in their adoptive land. When other methods of control fail conservationists have been resorting to what I would call fighting fire with fire: bringing another introduced species to control the one that has become a pest. These are the so called biological controls or biocontrols. This method is a partial admission of defeat. It allows the invasive species to remain but minimizes its impact. The National Wildlife Federation says it best:

In vast natural areas such as the Everglades, where spraying, snipping or bulldozing exotic weeds is out of the question, a well-tested, well-behaved bug is the conservationist’s best weed whacker.