By Dr. Rich Guggenheim, Plant Health Certification Program Manager, CO Dept. of Agriculture, Division of Plant Industry

Dr. Rich Guggenheim, Plant Health Certification Program Manager for the Colorado Department of Agriculture’s Division of Plant Industry, has crafted an insightful write-up on the Japanese beetle, a persistent threat to our green spaces, below. As part of ongoing efforts to combat the spread of this invasive pest, Dr. Guggenheim calls on community, county, and municipal leaders to join forces in educating the public and taking proactive measures. Feel free to share this information and contact Dr. Guggenheim with questions or for further assistance.

History

The Japanese beetle was discovered at a nursery in New Jersey. It is believed to have come in on nursery stock used in the 1916 World Fair. Currently, the beetle is established in 28 states with detections in an additional 13 states including Oregon, Washington, Idaho, Utah, Wyoming, Montana, and Arizona. The Japanese beetle was first discovered in Colorado in 1995 when trapping began to determine if and where the Japanese beetle was located. The North American Harmonization Plan between the US and Canada was established in 1998 to help control the spread of Japanese beetle across the US and prevent spread to uninfested states. Colorado’s External Japanese beetle (JB) quarantine was established in 2009. To date, no eradication efforts were initiated.

Lifecycle 

The Japanese beetle’s life cycle lasts one year. In the summer, they typically emerge around late June to early July as adults when they fly, mate, lay eggs in the soil, and die. Adult life span is anywhere from one to two months. The eggs hatch as grubs during autumn and feed on the roots of turf grass. Larvae move deeper into the soil during the late fall and winter, moving back up in the spring to resume feeding and emerge as adults in the summer.

Damage

Japanese Beetles cause damage in both the larval and adult stage. Larvae feed on the roots of grass, damaging turf. Injury by the adults is more obvious and is usually the primary concern in Colorado. Adults feed on leaves, buds and flowers of many common garden and landscape plants. They also cause significant damage to fruit trees and grapes, which causes significant concern to Colorado’s fruit industry. Leaf feeding is usually restricted to the softer tissues between the larger leaf veins, which results in a characteristic feeding pattern known and described as “skeletonizing”. More generalized ragged feeding typically progresses from the edges inward and produces a very ragged-appearing leaf. This damage can reduce photosynthesis and thus plant vigor. This often occurs on softer tissues, notably flower petals. Rose flowers are particularly susceptible to Japanese beetle injury. Damage on individual plants may be patchy and concentrated where aggregations of feeding beetles occur.

Spread

Since their introduction into the United States, Japanese beetle have spread primarily through infected plant material. To help protect Colorado’s economy and environment, Colorado established our External Japanese beetle quarantine in 2009 as well as establishing an internal quarantine in 2018 that includes 11 Front Range counties to help reduce the spread to parts of the state that are not currently infested, such as the the Western Slope and Eastern Plains. Plant material, including nursery stock and turf, should not be moved from the Front Range to other states or parts of Colorado. The best practice for any type of nursery stock or turfgrass is to buy it locally, from a licensed and inspected nursery or landscape contractor. 

Management

Japanese beetle grubs can damage turfgrass in the same manner as other turfgrass white grubs. Some cultural practices can limit damage and applied chemical or biological controls may also be useful. However, control of Japanese beetle larvae in a yard will have very little, if any, effect on the number of Japanese beetle adults feeding on trees, shrubs and garden plants. The insect is highly mobile so that problems with adult beetles typically involve insects that have moved a considerable distance.
Watering can have several effects. Japanese beetle eggs and the tiny early stage larvae are very susceptible to drying. If the top couple of inches of soil in a lawn can be allowed to dry a bit during the time eggs are being laid and hatching – July and early August – then many may be killed.

Biological control options with limited success include use of parasitic nematodes and strains of bacterium called  Bacillus thuringiensis, and a relatively new one called Milky Spore.

There are several insecticides that can be used to help control damage by adult Japanese beetles. These different insecticides vary considerably in features such as how long they can persist and control beetles, what plants they can be used on, whether they move systemically in the plant, and their hazard to desirable insects, notably pollinators.
Several insecticides are presently available that can provide excellent control of Japanese beetle grubs in lawns. Most commonly available are insecticides that are applied preventively to kill young grub stages. These include imidacloprid (Merit, Zenith, several retail products), chlorantraniprole (Acelepryn, Scott’s GrubEx), and chlothianidin (Arena), all of which can provide control of Japanese beetle larvae over an extended period (several weeks-months). Applications of these types of products are best made just before eggs hatch or shortly after this time (typically mid-June to early July). When using pesticides of any type, always read and follow all label instructions. It’s the law!

*No product endorsement is intended or applied. Those listed are for educational purposes only.

Quarantine and regulation in Colorado

Action items:

Education

CSU Extension has a factsheet homeowners can reference regarding this beetle. The information will help homeowners and the general public understand how to identify and control the beetle in their yards. One of the most important things homeowners can do to prevent the introduction of invasive insects is to buy plant material locally from licensed and inspected nursery dealers and hire landscapers that are licensed by the Colorado Department of Agriculture.

Homeowners can help prevent the introduction of invasive insects such as the Japanese beetle by adopting policies that foster Colorado friendly landscaping practices and buying nursery stock and sod from local suppliers who are licensed, encourage the use of xeric shrubs, and native plants, and reduce or eliminate non-functional turf. HOAs can also develop policies to ensure that landscape contractors are licensed and following all applicable laws regarding the quarantine in Colorado.

To help protect their communities from what is often expensive and difficult eradication or management efforts of invasive pests, municipalities are encouraged to help ensure compliance with these regulations in their own municipalities and educate business and residents on the importance of the Nursery Act to stop the spread of Japanese beetle and other invasive plant pests.

Enforcement

• Colorado Revised Statutes 35-26-106 requires anyone who distributes plant material in Colorado to have a current nursery license. This includes landscapers, nurseries, and greenhouses. This helps to:
  • To protect the nursery and landscape industry.
  • To protect consumers and
  • To protect Colorado’s ecology
    
• Nurseries, and Greenhouses – Must show Japanese beetle mitigation efforts in order to ship their plant material to states west of Colorado or, if operations are located within the 11 quarantined counties on the Front Range, in order to ship to other uninfested parts of Colorado. 

There are 5 types of mitigation certification depending on size and the intended destination of the plant material:

• Japanese beetle free greenhouse or screenhouse
• Chemical treatment
• Pest-free window from Oct. 1 to May 31.
• Pre-harvest soil treatment
• Negative detection trapping

• The Colorado Department of Agriculture provides seasonal trapping technicians for nurseries or greenhouses that want to use negative detection trapping certification.