European lily leaf beetle a culprit in Maine gardens since 1997

Q. Last summer all my of my lilies were devoured by orange bugs (ladybug size). I looked in all my insect books and could not find them. Many of my friends had their lilies eaten also. Have you any idea what bug it was, and how to prevent the same thing from happening next summer? – B.B., Kenduskeag

A. Most likely the culprit is the lily leaf beetle, scientifically known as Lilioceris lilii.

This pest, native to Europe, has been established in areas of Canada around Montreal since the 1940s. It first appeared in the United States in 1993 in eastern Massachusetts and is now present in Maine.

In 1997, the lily leaf beetle was reportedly found in home gardens in York and Ogunquit. In 1999 the Maine Department of Agriculture reported that it was feeding on lilies by mid-May and in Bridgton and Wells. The pest rapidly expanded its range northward: by 2003 the beetle had spread to every county except Washington and Aroostook and caused significant damage to all true lilies in some areas.

The University of Rhode Island experimented with the field release of parasitic natural enemies of the lily leaf beetle in infested New England states. An organism known as Tetrastichus setifer – which exists as a parasite on the larval stage of the lily leaf beetle – was released in Bridgton in 2003. The project met only limited success.

As mentioned, the lily leaf beetle attacks all true lilies and doesn’t bother dining on daylilies. Researchers believe that the pest arrived somewhere around Cambridge, Mass., in a shipment of lily bulbs from Europe. The insects are strong fliers and can also be moved from one area to another on host plants.

While the critter is nestled on the leaf of a lily plant, the gardener will notice the beetle’s striking bright scarlet wings and contrasting jet black head, antennae, legs and undersides. Adults are 3/8 of an inch long.

When one examines the lifecycle of the lily leaf beetle, it’s no wonder how it swiftly spread across New England. The insect overwinters in soil and plant debris. In early spring, the adults emerge to mate and lay eggs. According to University of Massachusetts researchers, the female lays between 200 and 300 eggs on the underside of leaves in clumps or irregular rows of two to 10 eggs. Some females can survive to lay eggs over two successive years.

Incubation of the eggs takes between five and 10 days. The newly hatched larvae feed on the underside of leaves while mature larvae feed on the upper surface of the leaves. The larval stage lasts 16-24 days and the larvae are typically covered with a protective case of excrement. The pupal stage lasts 20-25 days and occurs in the soil within a secreted cocoon.

It is not uncommon for the beetle to produce up to three generations per year.

Both the adults and larvae feed on lily foliage, often consuming all the leaves and killing the plants. The Maine Department of Agriculture advises that the lily leaf beetle may be controlled by regular hand picking if the infestation is minimal or with general garden insecticide such as Sevin. Most damage may occur in June and July. Gardeners have reported seeing all lifecycle stages of the beetle on lilies in early July.

Q. I know apple trees are supposed to be pruned in winter, but when should I prune my peach trees. I have two 4-year-old trees that are badly in need of opening up. – Manny D., e-mail

A. In general, pruning trees during winter is desirable for several reasons. From the point of view of the person pruning, certainly the branching structure of the specimen is more easily seen in the absence of leaves.

Winter pruning is also called dormant pruning. Remember dormant trees are still living, and are therefore potentially susceptible to injury by severe winter cold and the bitter affects of wind. Pruning should begin as late in the winter as possible to avoid winter injury. In the home orchard, the hardier and older trees should be pruned first. (Younger trees are more prone to winter injury from early pruning.) Apple trees should be pruned first, followed by cherry, peach, and plum trees.

A good rule to follow is to prune the latest blooming trees first and the earliest blooming last.

Although it is possible to prune peach trees in winter – mid-March, perhaps – a good deal of investigation points to evidence that pruning peach trees in the early winter can reduce their cold-hardiness. Trees pruned in the midst of harsh winter weather may have poor flower bud survival, dieback of tender young shoots and injured bark.

Considering the difficulty with which peach trees accept dormant pruning, it is perhaps wise to prune a little late than too early. In other words, the cautious gardener should prune in spring after budbreak. Pruning peach trees during bloom or shortly after bloom may not be ideal, but it will not adversely affect the growth of the tree or the fruit.

Diana George Chapin is the NEWS garden columnist. Send horticulture questions to Gardening Questions, 512 North Ridge Road, Montville 04941 or e-mail dianagc@midcoast.com. Selected questions will be answered in future columns. Include name, address and telephone number.