How to Help Your Trees & Shrubs Survive a Japanese Beetle Invasion

This spring and summer Denver residents have spent more time than ever tending to their gardens, making additions to their landscaping, and beautifying their homes.  Caring for the plants and trees on your property can feel therapeutic and release pent up stress during these difficult times. 

As we all strive to stay safe and socially distanced during the COVID-19 pandemic, home has become our refuge. The front porch, outdoor patio, and garden areas provide a welcome retreat for relaxation and escape. 

Many Denver locals are going all-out on their gardens this year, but are dismayed to find that an old foe is back in the flower beds. The destructive Japanese Beetle is on the verge of an all-out invasion. Imagine putting in hours and hours of hard work, only to have your gorgeous rose bushes skeletonized before your very eyes! 

Japanese Beetles don’t just target flowers, they also deal serious damage to several trees species native to the Denver region such as American Linden, American Elm, and Norway Maple. Learn more about this pest and how to protect your trees and shrubs from impending invasion.

Japanese Beetle Basics

First recognized in Denver in 2006, Japanese beetles have grown enormously in population since then, becoming an unwanted part of the Colorado landscape. The county has tried tirelessly to curb these pests, but the Japanese beetle continues to spread and cause more damage each year. 

Recognizing The Japanese Beetle

Japanese beetles are easily recognizable by their metallic green shell. The beetles may look pretty, but they are considered one of the most relentlessly destructive urban pests in the US!

  • Japanese beetle adult: identifiable by its oval form, which is about 7/16-inch in length. Its Torso is bright, shiny emerald green, and its wings are copper-colored. On the sides of its body are five patches of whitish hairs. On its head and fan-like antennae.
  • Japanese beetle larvae: a grub can be identified by its milky white body, dark head, and the legs on the thorax that are well developed. The body often curves into a C-shape. To distinguish Japanese beetle grubs from other varieties, look for a pattern of hairs on the hind end of the abdomen which forms a distinctive V-shape.

Japanese Beetle Life-cycle

According to Colorado State University experts, the Japanese beetle has a one-year life cycle. Adults may begin to emerge from the soil in early June and are usually in full force in early summer – from late June through early August. However, some adults may be found well into September. Japanese beetles remain active until the soil temperature drops below 50 degrees.

Adult beetles actively feed and mate on foliage and flowers of their host plants. Seeking out moist soil, adult beetles lay a small cluster of eggs among the plant roots daily. A total of 40-60 eggs may be laid by each Japanese beetle female during the course of her 4-8 week life span!

Fast Facts

Here are some other pertinent facts on the Japanese beetle from the Colorado State University Extension:

  • Japanese beetle adults chew flower blossoms and leaves of many commonly grown plants.
  • Japanese beetle larvae are a type of white grub that feeds on the roots of grasses.
  • Adults are best controlled by handpicking or by use of certain insecticide sprays.
  • Japanese beetle traps can capture many adults, but do not reduce damage to nearby plants.
  • Japanese beetle larvae can be controlled with certain insecticides or by insect parasitic nematodes.

At-risk Trees, Plants, and Shrubs

There are 300 plant varieties that the beetles crave and prey on, but here are the ones at the top of their list:

  • Virginia Creeper
  • Rosebush
  • American Linden
  • American Elm
  • Norway Maple
  • American Mountain-ash
  • Crabapple & Appletree

Not sure exactly what varieties of trees are on your property, wondering f they are a risk? Schedule one of our expert arborists to come out for a quick consultation! They are happy to help you identify your tree species and advise on next-steps for proper care.

Japanese Beetle Destruction

What does it look like when a tree or shrub is infested by Japanese beetles? Here are some classic signs:

  • Skeleton-like leaves: Japanese beetles devour the tender parts of the leaves, leaving veins. The result is severely damaged, lace-like leaves. They do not fall off, instead the leaves hang on the branch until they dry out.
  • Scorched appearance: Trees with a very severe infestation can develop a scorched look to the bark and leaves.
  • Beetle activity: Japanese beetles are not sneaky! They can easily be spotted flying from tree to shrub, feasting on leaves. If you have a Japanese beetle infestation, you will see them be especially active on warm sunny days.

A Japanese beetle can wreak havoc on your landscape leaving terrible damage. Luckily there are preventative measures you can take and treatment options for stopping these pests in their tracks.

Treatment Options For Japanese Beetles

If you google treatments for Japanese beetles, you’ll come across ads for traps. County officials, however, warn that due to population size and explosive growth of the beetles traps have essentially been rendered useless. Repeated trials have demonstrated that the use of such traps does not reduce the number of beetles damaging nearby vegetation.

Handpicking is another possible option, but is only partially effective when employed in small plantings. Beetles can be easily picked off or you can shake infested plants over a collecting container in the early morning. This strategy is still hit or miss, and yields unreliable results.

Lepitect Insecticide

Lepitect is an environmentally safe soil injection insecticide. It is a unique solution that provides rapid results, delivering systemic control of many key shade tree pests. It is a highly effective tool for the management of Japanese beetles. One application of Lepitect will give 30 days of efficacy for insect larvae.

Lepitect Comes In Two Forms:

  • The soil injected form of Lepitect treats 25 inches of tree diameter (DBH) at a high rate and 50 inches at the low rate.
  • The tree injected form of Lepitect treats 71 inches of diameter (DBH).

How Soil Injection Treatment Works

Soil injection of Lepitect involves placing chemicals in liquid form near the roots in the soil for root uptake. The chemicals are water-soluble, similar to other injection methods. For best results, Lepitect will be applied to soil that is moist, but not soaked.

With soil injection, also called the soil drench method, the insecticide is mixed in water and simply poured on the soil near the tree’s root crown. For this to work mulch or other surface organic matter has to be pulled back. The chemical must be poured directly on the soil. Afterward, the mulch can be replaced.

Soil injection methods vary somewhat, but typical recommendations are to inject chemicals 2–4 inches deep with a high-pressure injector either within 18 inches of the trunk or on a grid. The amount of Lepitect to be applied depends on trunk diameter, and diameters are added if multiple trees are being treated in an area.

Trunk Injection

Trunk injection is another application option. Injection of Lepitect into a tree trunk directly applies concentrated systemic pesticides into a tree’s vascular tissues for faster translocation. Trunk injection has the same benefits as soil injection, in that the pesticide quickly enters the tree’s vascular system. Both applications of Lepitect are particularly effective in controlling some of the most troublesome insect pests, like Japanese Beetles and Aphids.

Here are details on how Lepitect is typically applied:

  • Application Method: Pull back landscape mulch, landscape fabric, and surface organic matter before making soil applications to ensure the solution is delivered to the mineral soil. Measure the diameter of the tree at breast height (DBH), 4’6” above the soil line. For multi-stemmed trees and shrubs, use the cumulative diameter of individual stems at the soil line instead of DBH.
  • Application Timing: Make applications to actively growing plants just prior to or when insects first appear. Repeat applications every 2 weeks as needed.

Advantages of Trunk and Soil Injection Lepitect

Some pesticides and insecticides can be dangerous to birds, other insects, and nearby plants if they enter water runoff. You can breathe easily and feel confident when you choose Lepitect to manage pests in your lawn. It is safe and environmentally friendly!

Environmentally conscientious advantages of trunk and soil injection Lepitect:

  • Little, if any, pesticide applied is wasted to drift or runoff, because it can be applied precisely to where it is needed in the tree.
  • Can apply Lepitect with trunk or soil injection during windy and rainy weather because there is no drift or runoff.
  • Trunk injections can be used on sites where soil treatments may not be practical, effective, or appropriate, including trees growing on excessively wet, sandy, compacted, or restricted-soil environments.
  • There is little non-target organism exposure; therefore, it is safe in environmentally-sensitive areas. Your nearby shrubs and plants will not be affected.
  • Injection methods for treating some of Denver’s troublesome pests, such as Japanese beetles and aphids, can be particularly useful.
  • During Lepitect soil injection application trees are not wounded.
  • The soil injection and trunk injection methods require very few tools and can be completed quickly.

Spending time in your outdoor space is precious during the spring and summer months. Your beautiful trees and shrubs create the serene atmosphere for all your favorite activities. Protect your lawn and landscape from spring pests with environmentally safe Lepitect. 

Schedule with one of our friendly certified arborists for a quick and free consultation. We can’t wait to help you eliminate Japanese beetles from your property for good! Contact us at Fielding Tree & Shrub Care for more information on this simple, safe, and effective solution!