The beetle we hate around here more than anything is the Japanese Beetle, and for good reason!  They show up usually in late June, around the time we think they are never coming back!  They eat, mate and propagate – that’s it!  In the meantime, they eat our plants, flowers and trees, making a lacy mess of them then lay eggs in soil, typically in grass.  In winter the eggs hatch into larvae that eat roots, killing the grass, giving us another reason to hate them. 

They buzz around our heads, and we can’t get rid of them! That’s because they have no natural enemies in Colorado.  Common methods typically employed in the control of Japanese beetles include planting resistant plant species and using mechanical traps designed to attract and trap the adult beetles.  There is quite the debate over the use of mechanical traps – some feel they attract more beetles while others think they are controlling.  In any case, if you decide to use this method, place the trap as far away from your plants as possible. 

Another common method is mixing a couple tablespoons of dish soap with water in a small (approx. two cup) container. Empty beer or soda cans work well because the beetles have even less of a chance to escape.  The soapy solution kills the beetles as they drop to the bottom and drown before they have a chance to release pheromones.  This requires a constant vigil on the part of the gardener (it’s best to do this at least once a day) and if you don’t like to touch beetles, this is probably not the method for you. Unfortunately, there is no spray that really works on these guys with any degree of success, and spraying also affects all the other insects in the vicinity such as our favorite pollinators like bees and aphid killers like lady bugs, lace wings and praying mantis.  Killing beneficial insects leaves plants venerable to other diseases and infestations as well.

There are other methods of controlling (sadly there is no eliminating) beetles.  Here are some suggestions:

• Diseased and poorly nourished trees and plants are especially susceptible to attack by beetles.  The more love (i.e. fertilizer, good soil, proper light and water) you can give your plants the less likely they are to have infestation.
• Japanese beetles are repelled by the scent of several plants, including catnip, chives, garlic, odorless marigolds, and nasturtiums. They also dislike the smell of geraniums, larkspur and chrysanthemums.
• It’s best to eliminate plants that attract these guys like Virginia creeper, grape vine, rose bushes and several types of trees including elm and fruit trees. (see below to follow a link to more information)
• Some annuals I have found that are not bothered by beetles are coleus, begonia, vinca, nasturtium, canna and trailing geranium. (see below for more information)
• The most effective way of lowering the beetle population is by using a granular grub control product called Milky Spore (there is an organic version).  It is broadcast to garden beds and grass areas during the summer and early fall and kills the larvae,(grubs) before they immerge into beetles. It tends to be quite expensive, so it’s great for small areas but difficult to use in large areas like parks.  Results differ but it usually takes at least a couple of years of application to see major improvement.

Resources:

• USDA page on Japanese beetles:  https://www.aphis.usda.gov/plant-pests-diseases/japanese-beetle This will give you pictures, their yearly life cycle and if you scroll down, click on “Controlling Japanese Beetles” you will find a list of plants susceptible and plants resistant to Japanese Beetles.
• Denver Urban Gardens: https://dug.org/gardening-resources/japanese-beetle-management/.

Thanks to Judy Hendricks, who oversees landscaping in Boulevard One for the BOCA Board, for this helpful article.  Judy works with Keesen Landscaping Management to keep this part of Lowry looking good.