Judging from the heat and humidity, the appearance of
fresh-picked zucchini on the table, and the arrival of certain insects,
summer is here. Imagine my dismay, while eating a freshly picked bowl
of raspberries, at finding a Japanese beetle. This year’s invasion by
the leaf-devouring, half-inch-long, colorful metallic-green critters with
coppery-brown wing covers has begun.
Adult beetles feed on more than 300 species of
plants, but they really like linden, birch, willow, apple, and peach trees and rose
bushes, grapevines and raspberry canes. The beetles chew the leaf tissue
between the veins, leaving a skeletonized leaf, but they also like to eat
flowers. Adult beetles, which are most active on warm, sunny
days from 9 a.m. to 3 p.m., are attracted to other beetles and damaged
leaves, so early control is the key to preventing a heavy infestations. You
have a couple of options: Handpicking adult beetles early in the morning
is one method of controlling an infestation. Hold a bucket containing soapy
water or rubbing alcohol beneath the infested leaves. Move the plant or
poke the beetles, and they will drop to their deaths. Heavily infested ornamental plants may be
sprayed with carbaryl (sold as Sevin), cyfluthrin (sold as Tempo or Bayer
Advanced Garden Insect Killer), or another pyrethroid. Always read and
follow label directions for the safe use of pesticides. An affected plant may look devastated, but Japanese
beetles only rarely kill woody plants. To learn more about these insects,
visit the University of Illinois Japanese beetle fact sheet, located at
www.ipm.uiuc.edu/hyg/insects/japanese_beetles/index.html Right now bagworms, whose larvae hatched at the end
of May, are feeding on evergreens in our area. These are a most notable
pest of evergreens such as junipers, arborvitae, spruce, pine, and eastern
red cedar. Evergreens may sustain severe damage because leaf loss can cause
branch death. The caterpillars also feed on deciduous trees and shrubs such
as maples and crabapples. Deciduous trees and shrubs that have been
infested generally produce a new flush of leaves and survive. As the name implies, bagworm eggs, caterpillars, and
larvae live in bags decorated with pieces of foliage from the plant. In the
fall, winter, and spring, the spindle-shaped bags hang from plants like
Christmas ornaments. Young caterpillars are an eighth to a quarter of an
inch long and initially cause minimal damage, feeding on the outer layer of
leaves. Older larvae are three-quarters to an inch long and consume entire
needles or leaves. Because caterpillars start feeding at the tops of trees
and shrubs, damage progresses down the plant. Caterpillars are best controlled after they have
settled down and begun to feed, about two weeks after the eggs hatch. As is
the case with beetles, you have the option of handpicking them from the
plants or using an insecticide. One application of insecticide during this
time provides a high level of control. A second application may be required
a week or two later. According to Raymond Cloyd, an entomologist with
University of Illinois Extension, insecticides recommended for control of
bagworms include the bacterium Bacillus
thuringiensis var. kurstaki (sold as Dipel or
Thuricide), cyfluthrin (Tempo), trichlorfon (Dylox), and spinosad
(Conserve). Insecticide is effective on the young caterpillars. Older ones,
in which the bags are at least 3/4 inch long, are difficult to control, and
females feed less as they prepare to reproduce. B. thuringiensis is effective
on young caterpillars, but the material must be ingested, so thorough
coverage of all plant parts is essential. Spinosad works by way of contact
and ingestion and is effective in controlling bagworms. Cyfluthrin and
trichlorfon are recommended for larger caterpillars, but, again, thorough
coverage is essential. The best and most effective control is
handpicking and destruction of bags, fall through midspring, which ensures
that overwintering eggs are removed before they hatch. For more information on bagworms and to view photos
of them and the damage they cause, go to Kansas State University’s
“Home and Horticultural Pests” Web page,
www.oznet.ksu.edu/library/ENTML2/MF728.PDF.
This article appears in Jun 22-28, 2006.
