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Flowers, Fruits, and Frass

Local and statewide information on a variety of current topics for home gardeners and market growers.

Killing Japanese Beetles Can Kill Bees

Posted by Kelly Allsup - Bugs

Killing Japanese beetles can kill bees

Japanese beetles are a jeweled menace of plants like roses, lindens, hibiscus and blackberries. They don't come from some elusive place in the south where they have been sunning themselves all winter but rather have hibernated in your lawn as a grub. When spring comes, overwintered full-sized grubs begin to feed on the roots of turf. Right before the adults emerge they pupate. The adult beetles feed and lay eggs for the next two months. Japanese beetles like to lay their eggs on irrigated turf in July and continue into August. Growing grubs begin feeding in August until October. It is important to know that killing the larvae in your lawn will not prevent the adults from dining on your landscaping because they are very strong fliers. The only reason to treat for the grubs is if they are too numerous in your lawn and causing damage. Treat for the grubs after adults are seen to get the smallest stage of the insect. If you can pull large sections of your turf up like a carpet and see at least 12 grubs per square foot, a lawn grub treatment is recommended. Japanese beetle adults typically emerge the fourth week of June in central Illinois. They feed for about six weeks, flying to new hosts every three days.

Japanese beetles are the most detested by homeowners driving them to the garden centers to buy chemicals to kills this menace. Master Gardeners receive hundreds of questions each season on Japanese Beetles. Chemicals with the active ingredient of Carbamyl, pyrethroids and permethrin are effective control on adult beetles, with each spray lasting a few days. A systemic insecticide, imidacloprid may also be applied as a granular or drench to the root system of susceptible plants to provide control. However his systemic insecticide, imidacloprid, has been shown to move into the flower pollen of various plants where they are picked up by pollinating insects including honey bees and bumble bees and carbamyl, pyrethroids and permethrin will kill pollinators and beneficial insects.

University of Illinois extension advocates alternative to chemicals such as of hand-picking. If you stop by Sarah's Garden and the David Davis Mansion you may see a Master Gardener knocking Japanese beetles off their heirloom roses into a jar of soapy water. Do this activity every morning or evening for the first few weeks. Some gardeners go to the extent of trimming off all their rose/hibiscus flowers to prevent the lure of yummy fragrant flowers. Japanese beetles like sunny locations and are attracted to foliage that has already been eaten due to feeding hormones left behind. It is necessary to remove all of the lacy foliage left behind to prevent further occupancy. Most gardeners agree handpicking and removal of damaged foliage can be just as effective as the above chemical means without the killing the declining honey bee and pollinator population.

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