The Pesky Japanese Beetle

Japanese Beetles have become a gardeners’ nightmare.  They are out in droves this year and it’s a battle to control the damage they are doing to your plants.  They love fruit trees and shrubs, Lindens, Willows, and many other plants in the Rose family.

The Life Cycle of the Japanese Beetle

Japanese Beetles are the adult phase of the grubs that you have in your lawn.  Here is the life cycle of the Japanese Beetle.

April-May

Have you seen damage to your lawn in early spring?  This is usually caused by skunks and raccoons digging it up to find grubs just under the surface of the turf.  Believe it or not, the skunks and raccoons are helping reduce the future Japanese Beetle population by eating them in their larval stage.   When soil temperatures warm up, the grubs move up to the surface and start feasting on grass roots.

Treatment:

• Apply Nematodes once the soil temperature is above 10 degrees Celsius.
• Rake out the disturbed lawn. Top dress with triple mix or lawn soil and overseed to repair and thicken up the weakened grass roots.

June

This is a quiet month for the Japanese Beetles.  Most homeowners have by now top dressed and overseeded their lawns and are enjoying the gardening season.

July

This is the time when the grubs pupate and the adult beetles emerge.  They start feasting on your plants and are very busy mating. 

Treatment:

• Handpick the Japanese beetles and throw them into a bucket of soapy water, or into your koi pond.  The fish love them! If you have chickens, they will happily gobble them up!

• Install Japanese Beetle traps

• Pesticides with an active ingredient of Pyrethrins or Permethrins will work as a contact killer (Bug-Tek, Trounce).  Please be aware that these pesticides are non-selective, meaning they will kill any organism that comes in contact with the sprayed surface.  This includes beneficial insects. 

August

The Japanese Beetles have finished mating and now descend on the lawn to lay their eggs.  The eggs hatch and become grubs.  At this time, think of them as very hungry adolescents that are feeding voraciously on your grass roots.  The grub will grow very quickly.

Techniques to reduce the Japanese Beetle population 

Hand picking

The least expensive technique to reduce the population count is to hand pick the Japanese Beetles and drop them in a bucket of soapy water to drown.

Japanese Beetle Traps

The traps consist of the bait, or lure, which contains a pheromone that attracts the Japanese Beetle.  The beetles then fall into the attached plastic bag, where they will essentially smother themselves.  There is much debate as to whether the traps make matters worse as you are now attracting the Japanese Beetles to your site.  In my opinion, based on the explosive numbers we are seeing this year, I reckon that if you have them, you may as well trap them and kill them.

Pesticides

Pyrethrins and Permethrins

Pyrethrins are a nerve toxin derived from the Chrysanthemum flower.  Yes, It is organic, but it is also non-selective. Pyrethrins are toxic to all organisms.  Pyrethrins use an oil-based carrier, so it’s not recommended for indoor use due to staining.

Permethrins are a man-made organic compound that act the same as Pyrethrins, except they can be water-based.  Please keep in mind that it is also non-selective and will kill all cold-blooded organisms (all insects, fish, reptiles) as well as potentially impact warm-blooded organisms.

If using either product to kill Japanese Beetles, avoid spraying the blooms as this will kill our pollinators. 

Insecticidal Soap

Insecticidal soaps basically clog the breathing pores of the insect.  It is not as quick acting as Pyrethrins or Permethrins, but can be somewhat effective.

Nematodes

Beneficial Nematodes can be very effective at controlling the grub population if, and only if, they are used properly.  Beneficial Nematodes are live, microscopic worms that essentially penetrate and kill the grub, then multiply inside the grub’s body.  They then seek out other grubs to continue this process.  There are 2 types of nematodes in Lawn Guardian, one that goes in the top 3” of soil and another that goes down to 7” in the soil. 

Lawn Guardian is 100% safe for people, pets, plants and even earthworms.  It is shipped on a sponge and contains 10 million nematodes, covering 185 m sq. (2000ft sq.)
Storage: 12 weeks in refrigeration Please note expiry date!
Timing: when grubs are present in soil at the end of August

How to store live Nematodes:

Nematodes are live insects that need to be refrigerated.  Treat them like milk… if you leave them in a hot car or on the counter too long, they will die and no longer be viable.

How to Apply:

Here is the trick to proper application of the nematodes.  The BEST time to apply the nematodes is after the Japanese Beetles have burrowed into the ground, laid their eggs and the grub is in its juvenile stage.  In our area, this will be towards the end of August-September.  They can be applied up to the first hard frost.  At this point, the grub is voraciously eating the grass roots. It also has thinner skin, making it easier for the nematode to penetrate.  It is IMPERATIVE that the soil be moist when applying nematodes.  The nematodes need moisture in order to swim down to the grub.  Make sure to water your lawn thoroughly before application, and to thoroughly water it for 3-4 days after application.  Applying nematodes when the lawn is dry will kill the live nematodes.  Do not apply the nematodes on a sunny day as they are UV sensitive.  It’s also important that your lawn be cut to 1-2” in height at the time of application to make it easier for the nematode to slide down into the soil.

Watch Video for installation instructions

Timing of Application

The application of Nematodes is NOT a one-time deal.  Follow the schedule of application below for success:

First year:

• In May, once the soil warms up to at least 10 deg Celsius.  This will kill any overwintered grubs.
• Late August-September to kill newly hatched grubs and prevent lawn damage throughout fall and early spring

Second year:

• Late August-September to kill newly hatched grubs and prevent lawn damage throughout fall and early spring

All subsequent years

• Late August-September to kill newly hatched grubs and prevent lawn damage throughout fall and early spring

Conclusion

There are methods to control the Japanese Beetle problem, some more effective than others.  With proper application of any method, and a collaborative effort, we will all see greater success in reducing the Japanese Beetle population. 

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