Published: May 20, 2008 08:55 am         

Answers to questions on Japanese beetles and pruning spring-flowering shrubs

Q: Is there a product that can be applied to my yard in the spring to kill Japanese beetle grubs?

A: Spring is the wrong time to treat Japanese beetle grubs. Apply grub control products to turf grasses in August or September when Japanese beetle larvae/grubs are most susceptible because at that point they are very small, close to the surface and are actively feeding.

May is the right time to target adult Japanese beetles that attack trees, shrubs or flowers by using one of the Bayer Advanced Garden systemic products: Bayer Advanced Tree & Shrub Insect Control Concentrate, Bayer Advanced Dual Protection Azalea, Camellia & Rhododendron Insect & Disease Control Concentrate and Bayer Advanced All-In-One Rose & Flower Care Concentrate. Mix with water according to directions on the package. There is no spraying. Just pour the solution around the base of any plant listed on the container as being safe to treat. (These products should not be used on food crops.) The plant roots absorb the active insect killing ingredient Merit®, also known by the chemical name Imidacloprid. The active ingredient moves up into the tree, shrub or flower then into the leaves. Insect pests die after eating leaves, flowers or other plant parts.

My personal experience has been with Bayer’s All-In-One Rose & Flower Care formula which controls adelgids, aphids, black vine weevil larvae, lace bugs, leaf beetles, leafhoppers, mealybugs, psyllids, thrips, and whiteflies in addition to adult Japanese beetles. The product not only promises to protect roses and other flowering shrubs from insects, it also controls diseases like black spot, powdery mildew, rust and southern blight for up to six weeks and feeds roots, shoots and blooms with a 9-14-9 fertilizer. Because it works from the inside, rain can’t wash away the insect and disease protection.

It takes a few weeks for the active ingredient to move throughout a large tree, so Tennessee gardeners should apply these or similar systemic products during May to have good insect control in place by June when the first Japanese beetles usually show up. Call Bayer’s toll-free number (1-877-229-3724) to ask questions about these products.

Q: When should I prune rhododendrons and other spring-flowering shrubs?

A: Proper pruning encourages better flowering. Badly timed use of pruning shears or loppers can have the opposite effect. Ornamental trees and shrubs which have just one bloom period during the spring or early summer, should be cut back after their blossoms fade. There is no need to rush to do the job but don’t delay past July 1. Shrubs that flower early in the season are described as blooming on “old wood.” In other words, flower buds form on new shoots but the blossoms don’t swell and open until next season after those branches have been around nearly a year. If this season’s growth gets cut off by late summer or autumn pruning or damaged during the winter, there may not be any blooms next spring.

Shrubs that flower after the end of June form buds on branches from this year also, but their blooms open this year on “new wood.” Shrubs that flower during late summer and autumn should be trimmed while dormant or just after the last frost in the spring.

Remondant or re-blooming shrubs have flowers throughout the season. They bloom on both new and old wood. Endless Summer hydrangeas are remondant so gardeners tending them don’t have worries about whether pruning at the wrong time will leave them without flowers.

Plateau Gardening is written by Tennessee Master Gardeners about home landscapes and gardening in our state’s Upper Cumberland Region. For answers to specific yard and garden questions or to learn how to become a Master Gardener, contact UT Extension Cumberland County, P.O. Box 483, Crossville, TN 38557, (phone 484-6743). E-mail inquiries to mgardenerrae@frontiernet.net. E-mail questions may be answered either individually or through future newspaper articles.