Let's Grow: Beating the invasion of Japanese beetles

Suddenly Japanese beetles are invading our gardens, stripping our favorite plants practically overnight. How do we combat this annual invasion, now and in the future? You need a long-term strategy to defend your garden from this devastating pest.

First, it’s important to understand one thing: unless you lure them with “Japanese Beetle Traps” (which release an irresistible fragrance to attract beetles from miles around into your yard), most Japanese beetles don’t come from miles away or even from your neighbor next door. The beetles munching on your favorite plants probably live their entire lives within a few feet of their chosen meal.

Japanese beetle grubs hatch in the soil and mature just a few feet from your favorite roses or shrubs. At this time of year they mature into shiny flying beetles, emerge from the ground and attack the closest food source. As they feed, they also mate. After an orgy of feeding and procreation, they drop down and burrow back into the soil to lay eggs, after which they die. The eggs eventually hatch and become grubs, feeding on plant roots until it’s their turn to mature and continue the cycle.

You need to break the life cycle of the Japanese beetle without attracting more beetles from elsewhere. The best way to do this is to kill the grubs while they’re in the ground. There are chemical grub killers like Diazinon that you can apply to your lawn and gardens during the grub feeding cycle every year, but these will kill beneficial insects and birds along with the grubs, and are poisonous to children and pets.

A long-term solution is to apply “Milky Spore” bacteria in the vicinity of the plants that Japanese beetles are attracted to. Milky Spore is a microorganism that gives grubs indigestion, after which they die from starvation. You can apply Milky Spore any time of year. The spores colonize and reproduce in the soil, harmful only to Japanese beetle grubs and nothing else. Their effectiveness increases over time, and they will continue in the soil for many years without reapplication. Milky Spore is expensive to apply, but one application can last for decades.

Japanese beetle grubs attract moles to your garden. Moles feast on Japanese beetle, cicada and locust grubs as well as earthworms, burrowing under lawns and beds in search of juicy treats. Eliminating the grubs helps keep moles from taking over your lawn and gardens, so the cost of Milky Spore pays you back with mole control as well.

You can always pick the beetles off the plant by hand and drown them, and this certainly helps. The beetles may be killed by dropping them into a bucket of soapy water. Hand collecting can be used to protect valuable plants when beetle activity is relatively low. Japanese beetles always drop before flying away, so if you hold a container of soapy water under them before you knock them down, they’ll drop right in and drown.

A faster way to kill mature beetles is to spray the foliage with permethrin-based insecticide, which kills after contact and also poisons the beetles when they eat treated foliage. Bonide makes a ready-to-use Japanese Beetle Killer that is super-effective and easy.

There are many good all-purpose sprays that kill Japanese beetles and also help with other insects and diseases. Bonide’s “Eight” insecticide spray kills virtually every garden insect on ornamentals, edibles and houseplants, including Japanese Beetles, and it’s available in a concentrate. “Eight” works better than “Sevin.” Bonide insecticides can be found at any Ace Hardware or well-stocked independent garden center.

Bonide’s “Rose Shield” is a silver bullet for virtually any insect or plant disease on any ornamental plant (not for edibles). It kills Japanese beetles on contact and by ingestion. It also stops existing plant diseases and prevents new ones. An old standby is the “beetle bagger”, which uses scent for bait, attracting Japanese beetles and trapping them. This method attracts beetles from far and wide, so you should place the trap well away from your prize roses!The presence of beetles on a plant attracts more beetles. When you spray or remove beetles daily, only about half as many are attracted to that plant compared to allowing beetles to accumulate. One of the easiest ways to remove beetles from small plants is to inspect the plants early in the morning (about 7 a.m.) when temperatures are lower and the beetles are sluggish.

Timing is everything with Japanese beetles. Pay attention and take steps to control them, or they can strip your plants in a matter of days.

Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are on the “Garden Advice” page at www.goodseedfarm.com. For more information is available at www.goodseedfarm.com or call GoodSeed Farm Landscapes at (937) 587-7021.

This article originally appeared on Lancaster Eagle-Gazette: Beating the invasion of Japanese beetles