Japanese Beetles in Colorado by Joyce D'Agostino

Photo courtesy colorado.gov

As gardeners, we often struggle with the unwelcome visitors to our garden, whether it be a disease, an invasive plant or an insect pest that causes damage. The Japanese Beetle is now present in Colorado and can do significant damage to landscapes and lawns. This insect is not native to the US and came to the East Coast about 1912. Because it is not a native species, it has no natural predators that help control it.

Scientists have been monitoring its movement across the US and have been working on methods of control. This beetle enjoys a wide variety of plants commonly grown here, especially those that are highly scented such as roses and grapes. 

View the attached picture to help you identify this beetle. It may look like other more common beetles you may see in your garden, but one distinctive feature are the tufts of white hair around the hind end of the abdomen that are unique to their species. 

Begin by regularly checking your gardens and landscape starting mid-summer. Should you spot Japanese beetles, one method of basic control is to remove them by hand and drop into soapy water. This works for small infestations. 

The Japanese Beetle sends out a pheromone that attracts more beetles to your area, so working quickly and on a daily basis can help cut down the number that are drawn to your area. Traps for Japanese Beetles contain this pheromone that will bring them to the trap but it also can attract more to your landscape so are not recommended. 

Read the attached Fact Sheet 5.601 to learn more about the habits of this insect. Tips include controlling the Japanese Beetle grubs in your lawn. The adult female lays their eggs in turf and some cultural control tips are included in this fact sheet for helping stop the develop of the eggs into grubs and then into adults. This has been found to help stop a large number of this pest before it develops and spreads without the use of pesticides.

If you choose to use other methods, the fact sheets listed below include scientifically tested biological controls as well as insecticides. Remember that these insects can visit the same plants that your pollinators are attracted to, so careful use and timing of these insecticides and using ones that have been tested for safety and effectiveness helps eliminate harming the bees, butterflies and other beneficial insects. 

For more research-based information on these insects, refer to these bulletins. If you have additional questions, please contact your local county Extension Service:

CSU Extension Fact Sheet 5.601: Japanese Beetle

CSU Extension Fact Sheet 5.516: Billbugs and White Grubs in Home Lawns

Colorado State University: Questions and Answers About Japanese Beetle in Colorado 

Colorado State University: Insecticide Options for Control of Japanese Beetle on Leaves and Flowers 

Trees Forever: Japanese Beetle