Landscape - Current Pests

The following are pests that are currently active in Delaware landscapes.

Tuliptree scale and magnolia scale crawlers are active. Horticultural oil and Distance provide good control.

Magnolia scale. Photo by Brian Kunkel, UD Extension

Tuliptree scales. Photo by Gerald J. Lenhard, Louisiana State Univ, Bugwood.org

European Hornets/German Wasps and Yellowjackets are very active. They are predatory natural enemies of other insects but may need control, especially where food or food crops are present.

Late season leafhooper and lace bug damage is showing up. On evergreen plants, (Azalea and Andromeda), a fall horticultural oil application may reduce lacebugs and their eggs that would potentially overwinter on leaves.

Information from the September 18, 2009 edition of the Ornamentals Hotline newsletter from University of Delaware Cooperative Extension.

Landscape - Current Pests

The following are some current pest problems in Delaware landscapes.

Septoria leafspot is one of several common diseases showing up now on flowering dogwood (Cornus florida) and silky dogwood (Cornus amomum). Some trees have numerous small angular spots on the lower branches that look like small dogwood anthracnose spots. It is too late for any chemical control.

This time of year we often see an increase of anthracnose on oak, maple and walnut. On oak and maple, look for large brown spots that follow the veins and some round spots as well. This late in the season no control is necessary. On walnut, the spots are irregular in shape, numerous and can cause premature defoliation. Again it is too late in the season for any control and the fungus does little to harm the health of the trees.

Puss caterpillars and other stinging caterpillars are actively feeding. Puss caterpillars have been found on Ilex and Acer.

Ground nesting wasps, yellowjackets, and hornets are active and becoming more of a nuisance as we approach fall.

Slime molds have been appearing on lawns especially after recent rains. Slime molds produce a gray growth over the blades of turf that give it a dark appearance from a distance. What you see is the reproductive stage of this primitive fungus. It is not harmful to turf and can be removed by cutting the grass. These are related to the slime molds that appear in mulched beds as white, pinkish red, and yellow blobs often referred to as the “dog vomit fungus”.

Information from the current issue of the Ornamentals Hotline newsletter from the University of Delaware Cooperative Extension.

Landscape - European Hornets Out Now

European hornets are now active in Delaware landscapes feeding on ripe fruits. The following is more information on this insect.

The European hornet is a large wasp resembling a yellow jacketsbut much larger. The European hornet is about 35 mm (1.5 inches) long and is brown with yellow markings. Nests are rarely constructed in open areas and are more likely to be found in protected areas such as tree cavities, bird houses, barns, or sheds. During the summer, these hornets feed on large insects such as caterpillars, grasshoppers, flies, and bees. European hornets damage a number of ornamental trees and shrubs including, lilacs, rhododendrons, birch, ash, and dogwood. The hornet gains nourishment from the plant sap and the bark may be used as nesting material. Workers expand the nest throughout the summer, and in the fall the next season's queens mate with newly emerged male hornets. European hornets feed on substances high in carbohydrates in the fall. These food sources include overripe fruits, tree sap, soft drinks, juices, and possibly honeydew produced by insects such as aphids or scales. This hornet is also known to attack small fruits such as grapes and consume the sugars. European hornets do not reuse nests and populations die off with the onset of cold weather. The only effective method of control is nest removal. A pressurized wasp and hornet spray with a range of 10 15 feet is desirable. Treatments should be made at dusk or after dark to ensure most of the hornets are in the nest. Caution should be used when treating hornet nests since hornets guard the nest, can sting repeatedly, and can fly at night.

European Hornet. Photo by Jessica Lawrence, NC State Entomology Department, Bugwood.org

Information from Brian Kunkel, Ornamental IPM Specialist, UD

Landscape - European Hornets Very Active Now

We have had samples of European hornets come into the office recently. This is the time of the year that these hornets change their feeding habits and can attack plants in the landscape. The following is more information.

The European hornet is a large brown heavy-bodied wasp with yellow and orange markings. It prefers to nest in hollow trees. Normally, European hornets feed on other insects - caterpillars, grasshoppers, flies, etc. At this time of year, they look for carbohydrates and begin to attack fruit and trees and bushes (especially ash and lilac). The hornets can chew into fruit and chew off the bark and girdle branches as they create wounds from which they collect sap. European hornets have a long workday, they will continue to fly into early evening so damage occurs over a short period of time.

Control is difficult and involves finding nests in the area. If nests are found, they can be treated with insecticides such as Sevin or numerous pyrethroids. Landscape sprays are usually ineffective.


Adapted from "EUROPEAN HORNETS HITTING FRUIT AND TREE BARK" By Lee Townsend in the current edition of the Kentucky Pest News from the University of Kentucky, College of Agriculture.