The Control of Japanese Beetles

You know it is summer in Denver when we start handpicking Japanese Beetles (Popillia japonica) off plants in our yards. The beetles favor roses, grape & Virginia Creeper vines, but the pests are generalists and attack many plants and trees found in yards. They appear in late June and persist through September. Rapid reproduction makes them challenging to control. They lay their eggs in lawns, and their grubs feed on grass roots before emerging as adults. By midsummer, these voracious eaters overwhelm many neighborhoods frustrating homeowners and gardeners to no end. The question is, what to do? Before we get into that, let’s discuss where the Japanese Beetle comes from and its lifecycle.

Quick Facts…

  • Adult Japanese Beetle attack over 300 commonly grown plants.
  • They put Colorado’s fruit and wine industry at risk.
  • They defoliate Elms, Birch, Lindens, some Maples, and fruit trees.
  • Japanese beetle larvae or grubs feed on the roots of turfgrass.
  • Control options include handpicking and the use of certain insecticide products.
  • Traps do attract and capture adults but are not that effective.
  • Insect parasitic nematodes and other biological controls show promise in controlling these insects.

Entomologists believe that the beetles entered the country in 1916 as grubs in the soil of Japanese Iris at a nursery near Riverton, New Jersey. Within four years, the beetle proved too prolific and widespread. Japanese Beetles spread to other parts of the country inside nursery stock. Experts thought the insect would not thrive in Colorado because of our dry climate. However, the widespread installation of sprinkler systems across the city transformed our urban landscape into a perfect breeding ground for the bug. In 2003, the insect first appeared in Cherry Hills Village, and within ten years, the insect now has permanent, reproducing populations.

Japanese Beetle Life History

Japanese Beetle lifecycle

 

A Japanese Beetle lives one year. Adults emerge from the soil in early June and start feeding and mating on the foliage and flowers of their host plants. Throughout their 4-8 week lifespan, the mated females lay eggs on grass lawns. They seek out moist soil, dig 2-3 inches down, and then bear a small cluster of eggs among the grass root system. Each female beetle repeats this process throughout the summer, laying 40-60 eggs.
Once hatched, the larvae seek out nearby plant roots for food. The grubs become full-size by September. High infestations cause dead spots on lawns. The larvae continue to feed into the fall and dig deeper into the soil to overwinter. When the weather starts to warm the following spring, the grubs pupate into adults emerging a few weeks later to start the cycle again.

The Japanese Beetle Double Whammy

It is a double whammy because both the larvae and adult stages damage plants. Adult damage is evident since the insects feed on leaves, buds, and flowers. They eat on the soft tissue between leaf veins leaving a feeding pattern called “skeletonization.” Japanese Beetles attack Linden and Elm trees. Large-scale infestations can defoliate trees. Also, their grubs feed on grass roots, eliminating the plants’ ability to acquire water, causing brown patches. Damage to individual plants and trees may be patchy or concentrated when large numbers of beetles appear.

Control of Adult Japanese Beetles

Handpicking

hand picking japanese beetles

In Denver, handpicking has become a morning routine for people determined to control these insects in their yards. It is best to pick them early before they are less alert and active. Handpicking is time-consuming but prevents feeding damage. Most people place the beetles in a jar with soapy water.

Insecticide and Biological Controls

Controlling Japanese Beetles with insecticide products is complicated because the pests are active at the same time as flower pollinators. Most control products are highly toxic to bees and persist after application. Be sure to apply in the early morning or dusk when bees are not active. There are systemic products available on the market as well. Homeowners concerned about bees should contact a licensed tree service company like Ross Tree to manage the Japanese Beetles in their yard. This Denver Post article discusses promising Japanese Beetle control products currently on the market. Believe it or not, Geraniums sicken these beetles. Geraniums contain a compound when ingested, paralyzes these pests. Homeowners should plant Geraniums around plants they want to protect.

Neem Oil

neem tree nuts

Neem oil comes from the tree Azadirachta indica, a shade tree that grows in India and South Asia. For centuries, the seeds have been used to make wax, cosmetics, oils, soap, and natural insecticides. Cold-pressed Neem oil is highly effective against soft-bodied insects and mites. The oil’s insecticidal activity comes from Azadirachtin, which acts as an ovicidal (kills eggs), larvicidal (kills larvae), and an insect growth regulator. Together these attributes make Neem oil effective against Japanese Beetles.

Neem oil makes the leaves taste bad, causing the adults will fly away. When ingested, the Azadirachtin cause the beetles larvae or nymphs to stop feeding, stunting their development. Apply the oil as soon as beetles are spotted and spray plants every seven days while beetles are feeding. To prevent leaf burn, apply Neem late in the evening.

How Do You Outfox Japanese Beetles and Grow Raspberries in Denver?

insect netting protecting raspberries from Japanese Beetles

Last year a neighbor decided that if he could not figure out how to outfox the beetles, he would dig up his raspberry patch and try to grow something else. The year before, Japanese Beetles devasted the patch. The neighbor placed garden netting over his raspberries and had a good crop.

His raspberry batch is 3-4 feet wide and 20 feet long, and he noticed that Japanese Beetles land on plants in the morning and late afternoon to feed. Once they land, they stay stationary and feed. Placing garden netting at those times stop the beetles from feeding on his raspberries. He removed the mesh in the late morning and put it back on the plants several hours before sundown. Interestingly, wasp and bee pollinators had no trouble flying under the net to gain access to the flowers. The Japanese Beetles seemed fooled by the netting or fly to other plants to feed. So this year, he will leave the netting on all day and let the pollinators do their work.

Japanese Beetle Grubs in Lawns

Japanese Beetle grubs

Lawn Care Tips to Control Beetles

Female Japanese Beetles lay eggs in turf grass during the summer. Like any other living thing, they take a path of less resistance. Setting mowers to cut grass at a higher length increases the amount of effort to lay eggs, so they fly elsewhere to lay their eggs. As a backup, lay down a grass grub killer to eliminate the bugs before they emerge as adults. Below are other control ideas:

  • Dryness kills the eggs and hatchlings, so watering enough to sustain the grass during the hottest months but allowing the turf to dry disrupts the Japanese Beetle breeding cycle.
  • In the spring, watering your grass longer but less frequently promotes deeper root systems.

What Does Not Work to Control Japanese Beetles?

Japanese Beetles are a big nuisance to serious and casual gardeners alike, so many opinions exist on treating these insects. Some work and some do not. According to the Park People, these controls waste time and money.

  1. Japanese Beetle Trapping

    Traps use floral-based compounds to lure the bugs into the devices. Mandatory mass trapping was a component of the successful Japanese beetle eradication in Palisade, Colorado. However, the piecemeal application of traps in Denver does not work. Ross Tree does not recommend traps for Japanese Beetle control. The big joke at the office is that the best way to keep Japanese Beetles out of a yard is to give neighbors traps as presents.

  2. Milky Spore

    Milky spore is a bacterium sold in powder or granular form to control Japanese Beetles. The product is not cheap, and it takes applications over several years to show any effectiveness. However, even after spending a lot of money on multi-year applications, effectiveness is less than five percent.

  3. General Insecticides

    Homeowners wanting to control Japanese Beetles with insecticides should use products specifically formulated to kill this Beetle. Broad-spectrum treatments do kill the beetles but also kill off beneficial bugs.

 

When To Call A Professional Tree Company?

Whether to treat Japanese Beetle yourself comes down to a value judgment by the individual. Many turn to professionals because it’s complicated for the following reasons:

  • The larvae and the adult beetle are both harmful to plants.
  • Product control of the insect is problematic because of the possibility of harming bees and other pollinators.
  • Correct timing and application are critical to the success of product treatment.
  • State and the Federal Governments regulate the use of these products, so follow all application instructions precisely.
  • Improper use is hazardous and may lead to water contamination.

Are you expecting a sizeable Japanese Beetle infestation this year? Protect your plants and lawn by being proactive by calling Ross Tree at 303-871-9121 or filling out this request service form.