An invasive beetle is decimating gardens across the Front Range, and there's no magic bullet to deal with it. From Colorado Community Media.
Japanese beetles have descended on Front Range landscapes, and annual spawning frenzies send waves of frantic gardeners in search of a solution. Each June, the half-inch-long, green and brown metallic beetles lay waste to an array of ornamental and vegetable crops, particularly on the southwest side of the Denver metro area. Though the beetles have appeared sporadically in Colorado in decades past, the current outbreak represents an entrenched population that experts say won’t be easily controlled. “I hate to sound doomsday, but I think it’s too far gone here,” said Larry Vickerman, the director of Denver Botanic Gardens’ Chatfield Farms. “We’re doomed to have to deal with them.” The beetles may have arrived as far back as the 1940s, though the current south Denver outbreak seems to have originated in Cherry Hills Village, said Laura Pottorff, program manager of Plant Pest Detection and Quarantine for the Colorado Department of Agriculture. In many south metro area communities, swarms of beetles drip from host plants for much of the summer, leaving skeletonized leaves behind. Grapes, roses, and vines like Virginia creeper are especially hard hit, though the beetles also devastate other popular trees like lindens, elms, apples and crabapples, according to a fact sheet prepared by Colorado State University. Grass lawns are also victims, as the beetles lay their eggs in irrigated turf. Hatching grubs then munch on grass roots, leaving dead patches. No single method is effective in controlling the beetles, though management strategies abound and tend to fall into a few categories, according to the CSU fact sheet: drying out landscapes to kill thirsty larvae in the soil; replacing plants that attract the bugs with native, xeric varieties; removing the beetles by hand; employing biological controls, such as bacteria and nematodes that damage grubs; and applying organic or synthetic pesticides. Experts recommend homeowners employ a comprehensive approach. Allowing lawns to go dormant from mid-June to mid-July can kill off grubs at their most vulnerable state, though the benefit may be limited. “The beetles that you see in your yard do not mature from larvae in your lawn. They fly in from large expanses of turf grass,” said Robert Cox, horticulture agent at the Arapahoe County Extension of Colorado State University. Replacing affected plants can also help. “We have a way to get rid of it, but it won’t be palatable to people here, because we want greenery, and we want more than just native plants in our yards,” Pottorff said. “We have to come to a happy medium — water less, incorporate more native plants, and we won’t have so many problems. We ought to embrace the climate we live in.” Picking beetles off affected plants and dropping them into soapy water is an important tactic, Cox said, though he added not to smash the beetles — doing so sends clouds of an attractant pheromone skyward. Biological controls are also largely inadequate, though not without merit. Milky spore, a bacteria that infects and kills grubs, must be applied several times a year for several years to take effect. “It’s only going to knock out maybe 10 percent of any grub population,” said Cox. “It will have some benefit once it’s pretty well established. You’re still going to get the same number of adults flying in as you did last year.” Nematodes, tiny worms that infect grubs in the lawn, can be effective, though short-lived, said Larry Hurd, a horticulturist with South Suburban Parks and Recreation who manages Littleton’s War Memorial Rose Garden, where last year he and CSU’s Dr. Whitney Cranshaw ran numerous experiments on control methods. “We found that (nematodes) have to be introduced in the spring, typically watered in, or when it’s raining,” Hurd said. “Nematodes do not overwinter in Colorado soil. Every year they would have to be reapplied. ” Lesser organic pesticides are wholly ineffective — garlic, hot pepper wax, citrus extracts and even neem oil do nothing. Bio-neem, containing azadirachtin — an insect growth regulator extracted from seeds of the neem tree, often labeled as “clarified hydrophobic extracts of neem” — is mildly useful, Hurd said. Imidacloprid, the active ingredient in many commercially available pesticides, readily kills adult beetles on leaves and larvae in the lawn, and is often sold in turf treatments and foliar sprays. However, it’s also a neonicotinoid (neonic for short) — one of a class of pesticides that are believed to be a factor in Colony Collapse Disorder, the phenomenon that’s killing honeybees around the world. “My recommendation is that if you have any weed problems in the turf, or any flowering trees in that lawn, do not use imidacloprid,” said Hurd. “If you have lindens, flowering crabapples, dandelions or white clover in your lawn, you should not use neonics at all.” Still, Pottorff called imidacloprid “the most effective of the pesticides,” and Hurd added, “I don’t think neonics should be removed from the market. They’re just another tool in the shed. If you understand how they work, and you’re taking the necessary precautions, you can use them to your advantage.” Carbaryl, sold under the brand name Sevin, is also tough on honeybees if sprayed on flowers. Pyrethroids, a class of synthetic pesticide derived from a compound found in chrysanthemums, can also wreak havoc on pollinators if not applied in strict accordance with product labels. Acelypryn is a newer pesticide, currently available in only a handful of products, that appears to be much less harmful to pollinators. Larry Vickerman, the Chatfield Farms director, isn’t rattled. “The Japanese beetle’s going to do some damage, but it’s not the end of the world,” Vickerman said. “We’ll have chewed up grapes and roses. That’s the price we pay for green lawns.”