The Japanese Garden Beetle was accidentally introduced to the United States in 1916. Before this period, the beetle was only known to inhabit Japan, where the insect is not considered a pest. The adult beetles have a life cycle of approximately 30 to 45 days. The pests devour plants from the top down, and consume 300 different types of plants. Not only does the adult Japanese beetle cause harm, so does the insect during the larvae stage, also referred to as a grub. Grubs live underground for about 10 months. The grubs can cause damage to grass and turf. Understand the proper methods of beetle and grub control to rid your yard of the pest.
Choose new plants for your garden that will not attract additional Japanese Beetles. Avoid planting roses, linden, grapes, sassafras, hollyhocks and horsechestnut. Choose trees and shrubs that are less attractive to the insect such as box elder, red maple, silver maple, boxwood and flowering dogwood. Visit with a local plant nursery or garden center for suggestions on plants to use and which ones to avoid for your area.
Shake the plants early in the morning to physically remove the beetles, suggests the University of Kentucky College of Agriculture. Allowing beetles to fall into a bucket of soapy water will kill the pests; the beetles are groggy and slow-moving during the early-morning hours and easier to remove at this time.
Cover plants with light cheesecloth to avoid being overwhelmed with infestation. Lightly cover the plant with cheesecloth and tie at the base. Avoid bending the branches, leaves or flowers.
Spray the plants, shrubs and flowers with an appropriate insecticide. Remember that different insecticides will protect plants for certain periods of time, some for a few days and others for a few weeks. Read insecticide labels and look for specific protection from Japanese Beetles. The University of Kentucky suggests products that contain the chemical cyfluthrin, bifenthrin, deltamethrin and permethrin. Carefully read all application directions. Avoid spraying right before rain or when it is windy outside. Pay close attention to the direction if you are spraying an edible crop; there might be a specific number of days you must wait between spraying the plant and harvesting food. The University of Wisconsin suggests spraying during the afternoon hours when beetles are most active.
Cautiously use Japanese beetle traps, experts at the University of Kentucky suggest. Understand that traps will attract many more beetles than actually caught. Don’t place traps near gardens, plants and flowers that will be eaten by the pests who are traveling to the traps. The path of destruction to the beetle trap might not be worth capturing only a small amount of the insects.
Control grubs by holding turf irrigation for about a week during the peak adult beetle flight. Ask a master gardening club or local nursery what time of year the most adult beetles will be present. Monitor your garden and lawn area for signs the beetles are increasing. Apply treatment directly to lawns from early to mid-August—carbaryl, diazinon and trichlorfon are three active ingredients in turf pesticides that help decrease the grub population. Use preventive controls, insecticides used prior to grubs hatching. Look for long-term treatments containing imadacloprid and thiamethoxam.