DENVER, Colorado — Japanese beetles have become a scourge upon many gardens in the metro area. To combat them, it's important to understand their life cycle.
In summer and fall, the beetles mate and lay eggs in lawns. They hatch and the grubs feed on the roots of turf grass. They persist through winter and emerge as adult beetles in late spring or summer.
Controlling the beetles starts with treating your lawn in fall and spring with a grub killer. This can be done in conjunction with applying milky spore, which makes the grubs sick and will stay in the soil to pass on to new generations.
The problem is that even if you treat your lawn--or don't have a lawn--the beetles will fly in from your neighbors.
The best method of control I've found is to use a soap spray. I mix about a tablespoon of Dr. Bronner's liquid soap in a quart bottle of water. Shake and spray the soapy mixture on the beetles. You must make a direct hit. The soap gums up their wings and they die quickly. Use a pure soap. A detergent will burn the leaves of your plants.
This isn't a preventative spray. You must hit them with the spray. I make my rounds to spray several times a day, checking the plants they feed on most frequently.
The objective is to reduce the population as much as possible and prevent them from mating. Eliminate as many as you can, whether they originated in your lawn or not. Traps can also be used in conjunction with routine spraying.
Avoid using insecticides that can kill beneficial insects such as butterflies, lady bugs and bees. Soap can also be used to control pests such as aphids, whiteflies and spider mites. A soap spray is effective when applied to the undersides of the leaves where they congregate. If lady bugs are active, let them take care of the situation.
Don't let the beetles ruin your summer. Use soap to make the best of a bad situation.
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