beetles2_mar17BY LINDSAY CUTLER

We left for France under the blue skies of early July 2016, marveled at the Eiffel Tower, ate bowls of steaming mussels with our children late at night, strolled the farmers markets, drank quantities of local wine, and…arrived home to an onslaught of frantic calls at our design and landscaping company. Forget jet lag – the Invasion of the Japanese Beetle had begun. Little did we know, even before we departed, lurking in the soil were the larva of this dreaded pest.

One client called in near tears – her house, previously green with Virginia Creeper had been decimated by the beetles. The beetles attacked from the base to the tips of the vines on every wall of her house. It all came down, leaving the previously lush green walls bare and white. Even after being sprayed with insecticide, the beetles were falling out in masses as we removed the vines. In places, you could hear them chewing.

My son was with us that day. I put his childish affinity for killing small insects to use. Unfortunately, that would only attract more.

We spent much of the next three weeks responding to urgent calls, driving across the metro area, hearing the same story each time. In some places it wasn’t so bad, but in others the infestation leveled whole neighborhoods. The quarantine email for nursery growers I received in mid-August confirmed that the Front Range is a zone of high infestation.

How did they get here and what can be done? First, a bit more about the nature of the beast.

Japanese beetles arrived in New Jersey from Northern Japan in 1916, probably on a plant. Not a problem in their home country where populations are checked by native predators, they quickly became a pest here, experiencing a virtual all-you-can-eat buffet on a host of garden plants. They made their way south and west, arriving in the mountain states around 2006. By 2009, an external quarantine was imposed on all nursery stock imported into Colorado and, in summer of 2016, an internal quarantine was passed, meaning that nursery stock from highly infested areas must be inspected and cleared of contamination before being allowed into areas of lower infestation. This quarantine is in effect for 11 counties along the Front Range for 2017.

The beetles spend 10 months of the year as grubs beneath the surface of our lawns, emerging in late June as adult beetles. They mate, lay their eggs, and die 4-8 weeks later. The grubs feed on the roots of lawn grass, causing visible brown patches in the later, drier months of August and September. The adult beetles feed on raspberries, beans, hollyhock, American linden, American elm, rose, silverlace, guara, rose of Sharon, Japanese maple, Peking cotoneaster, crabapple, basil, grapes and about 300 more plants. They eat the soft leaf tissue in between the veins of the leaf, resulting in the now-familiar skeletonized leaf. With this tissue gone, the plant cannot adequately photosynthesize and may die.

Once an adult beetle finds a choice food plant, it emits a pheromone inviting others over for the feast. If there is one Japanese beetle on your whirling butterfly, there are bound to be dozens more on the way. What’s more, if you pluck that one and squish it, it emits that same pheromone, bringing the party to the scene of the crime.

With effective quarantines, we can slow the spread of the Japanese Beetle, but the Front Range is already heavily infested. For Denverites, this pest is likely to be ubiquitous for the foreseeable future.

Things you can do:

1. Inspect your plants weekly beginning in July for signs of beetle incursion.

2. Drown the beetles in soapy water. They do not have a very firm grasp and can easily be shaken off into a bucket.

3. Water more deeply, less frequently. Allowing your lawn to dry out between waterings not only promotes deep roots and reduces long term water needs, it also dries out the grubs, killing them. Bonus – adults prefer to lay their eggs in cool, moist spots in the lawn.

4. Mow high. Or rather, mow long. Grass kept at 2 ½-3” height will grow deeper roots and need less water. All ages and stages love a moist lawn so CONSERVE.

5. Avoid buying plants they love. Really, the only way to eradicate them is to deprive them of their food source. However, if you can’t live without fresh green beans, be prepared to fight the uphill battle…and endure the glares from your neighbors as they pluck and drown each one now munching on their apple tree.

6. Plant a diversity of plants to encourage natural pests. Bringing in native predators such as parasitic wasps, birds, and flies can control outbreaks, resulting in a balanced community with the resiliency to fight off infestations.

7. Incorporate plants that the beetles abhor such as lilac, forsythia, dogwood, magnolia, and American holly. Diversity creates a strong community of beneficial nematodes, pollinators, predators, and soil microbiota, limiting infestations to a tolerable threshold.

8. Call a pro. The Master Gardeners at Colorado State University Extension are there to answer all your lawn and garden questions. They are backed by extensive research and armed with hundreds of volunteers to help you. For best results, contact your local county extension office.


1. Freak out and let your child go on a beetle killing spree – this will only attract more (beetles, not wild children).

2. Head to your nearest big box store to buy an arsenal of insecticides. Most insecticides are only effective before damage is visible – in mid-July when the eggs are hatching. These insecticides impact the entire insect community which (see item 6, above) is not good. If you must spray, look for the ingredient chlorantranipole as it poses a lower risk.

3. Buy traps. Remember the pheromone? Where one beetle is, many more will come and your house will be fraternity row.

4. Rip out all your plants. Again – there is strength in diversity and as surely as the pendulum is swinging away from certain plants, something in our future will surely swing it back.

5. Take plants to your friends in Winter Park (or Palisade or Vail…). That’s like sneezing on the handle of the coffee pot at work, spreading infection to the uninfested.

Leave to the pros:

1. Biological controls such as milky spore or sprayed-on beneficial nematodes. While these can be effective, they must be applied during the right time of the year under certain weather conditions.

2. Chemical controls. Again, these can be effective but are not recommended if grub population is less than 20/sf in the lawn due to their adverse environmental effects. Though Japanese beetle grubs are distinct from other grubs, the identification is better left to an entomologist. Additionally, brown patches on the lawn may be attributable to many other things such as disease, drought, or thatch. Insecticides will not remedy most of these problems. Once brown patches do appear as a result of grub damage, it is far too late to control chemically since the grubs are very large at this time of year and will not readily die.

The Japanese Beetle problem rears its ugly head in some years worse than others. They are only active when soil temperatures are above 60 and soil moisture is high. Given the heat and aridity of winter thus far, there will likely be water restrictions this summer. Observing these restrictions not only saves water but can significantly reduce your exposure to the damage wrought by this beautiful killer.

For more information contact Lindsay Cutler at Cutler Design Group 303.859.5519 or

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