Those Pesky Summer Insects are Back

The typical summer insect pests are starting to appear throughout Missouri. We are also collecting Japanese beetles in traps in central Missouri. This is the earliest we have trapped this insect in this area.

Japanese beetles have recently been found in urban areas in Missouri and can be quite destructive to lawns, trees, flowers and fruits. The adult beetle is about ˝ inch long and is metallic green and bronze with a row of white tufts of hair on each side of its body. Japanese beetles resemble green June beetles, but are about 1/3 the size of green June beetles. Adult beetles are usually spotted in the garden from mid-July through August. They are especially fond of roses, grapes and flowers of all kinds. The larval stage is a typical white grub and feeds on the roots of grasses and primarily damage turf. If you find beetles that resemble Japanese beetles, please contact our office for assistance in identification as we are trying to ascertain the distribution of this insect in central Missouri.

Another beetle that wreaks havoc in home gardens is the blister beetle. Blister beetles range from ˝ to 1 inch in length and are easily recognized by their characteristic shape: narrow and cylindrical, with a distinct “neck-like” appearance when viewed from above. Their colors range from black to gray to brown, and some species have orange stripes. Blister beetles appear in late June and early July and feed on the leaves and flowers of most plants. They can cause serious damage and can completely defoliate many plants such as clematis on an annual basis. Blister beetles also produce a protective toxic chemical, cantharidin, which is released when they are disturbed or crushed. This chemical can cause blistering of the skin, especially tender skin. Blister beetles are also highly toxic to some livestock, including horses, which sometimes eat them in alfalfa hay. Blister beetles usually travel in groups and tend to mass in one area of the garden. Blister beetles come into the garden quickly, feed heavily and disappear quite abruptly. They tend to feed on the same plants from year to year; thus, you can protect your plants using row covers or shade cloth. Blister beetles are also usually easily controlled with several garden insecticides.

And for those of you wondering what happened to your hollyhock and columbine leaves? Many plants were attacked heavily this year by leafmining insects. Leafminers are the larval stage of various insects, that upon hatching from the egg, tunnel into the leaves between the upper and lower surfaces to feed on the inner part of the leaves. Sometimes, these insects will skeletonize the leaves until nothing is left such as was the case with hollyhocks this year. Other plants commonly attacked by various species of leafminers include larkspur, nasturtium, verbena and chrysanthemum.

We are also seeing heavy aphid infestations on many different plants including trees and shrubs, annual and perennials and tomato plants. Aphids, sometimes called “plant lice,” are among the most common insects that can attack home, garden and landscape plants. Aphids have an extremely high rate of reproduction, which enables insect numbers to build up very rapidly. When aphid numbers are high, plants are stressed and therefore less vigorous. Aphids damage the plant by piercing the leaves, stems and flowers and sucking sap and other fluids, weakening plants and leaving them discolored and stunted. Foliage may look puckered or distorted. Aphids have many natural enemies that successfully attack them and provide very effective control. They are a favorite diet for ladybird beetles which eat entire aphids. One ladybird beetle can eat up to 100 aphids per day. Encourage natural enemies of aphids by using synthetic insecticides as little as possible. Before treating any plants, thoroughly inspect the plant for presence of natural enemies. Aphids can be knocked off the plants with a strong spray of water every couple of days. Aphids tend to congregate on the under sides of the leaves; thus, you need to spray water under the leaves as well as on the tops. Insecticidal soaps or horticultural oils also work well to control aphids. It is best not to apply insecticidal soups or horticultural oils in direct sunlight as they can have phytotoxic effects on the plant. Heavy aphid infestations can be difficult to control if aphids hunker down in the folds of leaves, flower buds or new growth. Aphid colonies can be reduced by pruning and disposing of aphid infested plant material and can also be controlled by squashing with fingers.

Mary Kroening, Missouri Master Gardener Coordinator and UMC Horticulturist, (573) 882-9633