Margaret Lauterbach

Idaho successfully battles destructive Japanese beetles

Japanese beetles feed on leaves at a vineyard in North Carolina.
Japanese beetles feed on leaves at a vineyard in North Carolina. The Associated Press

For more than two decades, I’ve been subscribed to gardening lists online, hearing complaint after complaint about the damage done by Japanese beetles. They shred ornamental plants’ foliage and blossoms, leaving sad havoc in their wake. Entire beds of roses were especially vulnerable. Some gardeners tried poisoning with milky spore disease, but then complained that it seemed to entice more beetles to their area.

I felt sorry for those gardeners, but a little superior, too, since we didn’t have those destructive insects in our area.

Then the boom lowered. Japanese beetles were found in Boise, having hitchhiked here on plants from an out-of-state nursery. We first knew they were here in 2012, mainly on the river level, from Pioneer Cemetery to Plantation Country Club. A total of 61 were found that year. The Idaho Department of Agriculture set out traps, and in 2013 trapped 3,058 beetles. I recall talking with the department’s entomologist at that time, Mike Cooper, and he sounded deeply depressed. He retired in 2014, after hiring Dr. Paul Castrovillo as the new entomologist.

The state has been proactive, putting down insecticides in areas where beetles have been trapped, starting in 2013. Letters are sent to landowners in March regarding the presence of those insects in that area, and informing landowners of the state’s intent to control the beetles with pesticide. That gives landowners over a month to obtain answers to any questions they may have, and to relay their consent or refusal. The insecticides then are put out in May and July with landowners’ permission. The numbers trapped have steadily dwindled after pesticide placement: 1,283 in 2014, 365 in 2015, 128 last year, and eight this year. They’ve put the same insecticide on lawns that lawn maintenance companies use to control billbugs and other lawn pests. Japanese beetles don’t feed on lawns, but they lay their eggs there. Granular Imidacloprid can control them there at less cost and less environmental damage than overhead spraying would.

Castrovillo said Oregon and Utah officials get court permission to apply insecticides if landowners refuse application since this control is so vital to the entire community. Idaho officials could go to court, but have had very few refuse the treatment, so officials just watched those properties carefully.

Cooper had told me that it had taken Salt Lake City seven years to eliminate an invasion of Japanese beetles. Apparently we’re very close to elimination, their pesticide methods evincing effective control. The Idaho Agriculture Department has put out an average of about 2,000 traps around the area to pinpoint their presence.

A different take on earwigs

Many Boise area residents are complaining about the numbers of earwigs they’re finding this year. When I first started gardening in Boise, in 1972, we were flooded with earwigs. I bought some preying mantis egg cases, and the following year we had a fraction of the number of earwigs we’d had the previous year. Entomologists are more prone to regard earwigs as beneficial, and preying mantises as destructive, however. Preying mantises are carnivorous, and will catch and kill honey bees and other beneficial insects for their own consumption.

Earwigs are regarded as beneficial because of their feeding on the eggs, young and even adults of other insects such as aphids, mites, and nematodes. Gardeners regard them as destructive because of their eating holes in leaves of plants such as radishes, turnips, and other vegetables, their startling effect as they emerge from a cut apricot or peach, and their appearance in general. Their pincers look menacing, but are not hazards for humans. Females use them to guard their eggs and young from cannibalistic insects such as other earwigs.

Earwigs are very difficult to control outdoors, since they spend most daylight hours in bark crevices, soil pores, under rocks and logs, emerging at night to feed on plants and insects. They overwintered in the soil or under rocks or logs, protected by a blanket of snow. It would have been warmer there than above the snow, where the air was frigid.

How do we control them? They are vulnerable to Safer’s Insecticidal soap spray, but you must actually spray the insect with that, instead of relying on residual effect. Soap spray has no residual toxic effect. We must take advantage of their preference for hiding in crevices to trap them. You can use corrugated cardboard or rolled-up newspaper, setting either in your garden paths where you’ve had the most damage. In early morning, go outside with a bucket of hot soapy water, and tap the cardboard or rolled newspaper against the brim so hiding earwigs are dropped into the killing soapy water.

Send garden questions to or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

Heat affects fish in outdoor ponds

Do you have a water garden, complete with koi or other tropical fish? This hot weather can damage them — the finny equivalent of being locked in the car. They need a place to get out of the hot sun, such as a hiding place in the pond or shade — under water lily pad. They also need vegetable-based food, and when the temperature is over 88 degrees, they won’t or shouldn’t eat at all.

Moreover, heated water contains less oxygen than tepid water, so your koi may need additional aeration, such as a pond pump stirring up the water and injecting air into the water.