Summer Pests in the Garden

This summer has been a busy year for insects in the garden. Many of the insects we are seeing in high numbers are attacking the garden earlier in the season than is typical. We have also seen an increase of Japanese beetles in the state; this beetle is a newly introduced pest for Missouri.

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 1/2 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 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 damages turf. If you find beetles that resemble Japanese beetles, please contact our office for assistance in identification, as this insect is a quarantined pest in Missouri.

Another beetle that wreaks havoc in home gardens is the blister beetle. Blister beetles range from 1/2 to one inch in length and are easily recognized by their characteristic shape: narrow, 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 in my garden they completely defoliate my buttercups 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 leaves? Hollyhock was attacked heavily this year by a leafmining insect that only attacks hollyhock, and, occasionally, hibiscus. 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 skeltonize 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 columbine, larkspur, nasturtium, verbena, and chrysanthemum.

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