.cat-links { display: none !important; }

Unwelcome summer garden pests

Two unwelcome summer garden pests

By John Chapin

Every summer, two nasty garden pests show up to plague homeowners in Central Indiana. Bagworms and Japanese Beetles appear like clockwork in midsummer to do their best to damage and disfigure flowers and shrubs. However, there are preventative steps that can be taken to mitigate the damage, as well as effective ways to deal with each pest when they do show up.

The caterpillar stage of a moth with the tongue-twister name of Thyridopteryx ephemeraeformis is commonly known as eastern bagworm or evergreen bagworm. Adult males resemble bees, with transparent wings and black furry bodies. Adult females are eyeless, wingless and maggot-like, with yellowish-white soft bodies. Newly hatched larvae are blackish, turning brown to tan as they grow, mottled with black and yellow-tinted heads.

Larvae build a “bag” of silk decorated with bits of plant material from the shrubs or trees on which they feed. This effectively camouflages them until they get some size (up to almost 2”) by midsummer and the plant bits turn brown and gray. Adult males transform into moths in mid-August after fastening their “bag” to a branch and pupating head down. Females never leave their cocoon, requiring a male which she attracts with a strong pheromone to mate with her through an open end at the back of the case. She dies with hundreds to several thousand eggs to overwinter safely inside her protective bag.

Bagworms most commonly feed on many types of evergreens, including arborvitae, junipers, pines, and spruces, but will also attack over 100 other species of trees and shrubs. They have few natural predators in urban areas and a voracious appetite, so they can be serious pests in home gardens and landscapes. If left unchecked, host shrubs and trees can be killed by bagworm infestations.

Preventative care includes picking off any bags in the fall when they are easiest to detect. If late spring inspection reveals young bagworms, spraying with insecticides will kill them. As they get older (and larger) they are more resistant to chemical sprays. However, various bacterial sprays such at Bt/Spinosad are very effective at any stage. Systemic insecticides can be used to “inoculate” favorite plants in late fall or very early spring for 12-month control.

Late June into early July is when Japanese Beetles, Popillia japonica, make an appearance in this area. This non-native pest was discovered in New Jersey in 1916 and is now a serious pest in 30 states east of the Rockies. The beetles zero in to feed on flowers, fruits, vegetables, and certain favorite ornamental shrubs and trees. They will be around for a month or so before mating, laying eggs and dying by late summer.

Preventative control can be done by killing the grubs. There are several turf chemical insecticides on the market to do this, but proper timing of application is crucial.  An organic solution is to establish a bacterial culture of Milky Spore disease in the lawn. Once established, which can take a year or more, grubs are killed by the bacteria thus eliminating the immediate beetle population.

For adult beetle control, there are insecticidal sprays, both chemical and organic, available at garden centers. There is disagreement as to whether or not popular beetle “traps” help or not. Some claim that they attract more beetles to landscapes than would normally be found. Many who use traps locate them away from gardens to minimize damage.

Several insect predators and parasitoids have been introduced to the United States for biocontrol. A few have become well-established and are beginning to have a positive effect on reducing Japanese Beetle populations. We can only hope!

Leave a Reply

Your email address will not be published. Required fields are marked *