How to Get Rid of Japanese Beetles and Grubs

Japanese beetles can be quite the menace for gardeners and homeowners alike. Their lifecycle consists of several stages, each requiring a specific approach to treating them.

The immature stage of the Japanese beetle—the white grub—typically has a three-year lifecycle. However, most of the damage to ornamentals and turf grass happens during the spring and fall of their second year. This is when grubs are present in the top inch of the root zone, heavily feeding on grass roots and thatch.

In the third year of the cycle, the grubs rise out of the soil as Japanese beetles. These beetles eat surrounding plants and lay eggs in the soil throughout the summer. These eggs eventually hatch into grubs, and the cycle begins again.

In this comprehensive guide from Blain’s Farm & Fleet, we’ll walk you through the necessary steps to tackle these pests at every stage of their life. From dormant grubs hidden beneath the soil to the feeding adults that wreck havoc on your plants, we’ve got you covered.

Stage 1: Dormant Grub (October – March)

In the colder months, Japanese beetle grubs burrow deep into the soil and go dormant for the winter. During dormancy, grubs are not actively feeding, but they are preparing for their next phase. They reside a couple of inches below the soil surface, making them hard to reach with topical treatments.

Actions to Take

• Aerate Your Lawn: Aerating helps break up the soil. This can expose grubs to cold temperatures, which can reduce their numbers.
• Use an Insecticide: Apply products such as BioAdvanced 24 Hour Grub Killer Plus for fast results in early spring or fall. Grubs will usually stop feeding and start dying within one day.

Stage 2: Feeding Grub (March – April)

As the weather warms up, grubs rise from their winter rest and begin feeding on the roots of grass and other plants, causing extensive damage. Look out for patches of dying grass that lift easily. Chances are, there will be white grubs underneath.

Actions to Take

• Apply Milky Spore: This natural bacteria specifically targets Japanese beetle grubs and is safe for the environment.
• Use an Insecticide: The best way to control adult beetles is to make a preemptive strike in the spring, well in advance of the adults emerging. Insecticides like BioAdvanced Tree & Shrub Protect & Feed Concentrate or BioAdvanced All-In-One Rose & Flower Insect Killer are best

Stage 3: Pupa (April – June)

After the spring feeding period during the third summer of their life, grubs transition into the pupal stage. This is when they transform into adult beetles.

Actions to Take

• Use an Insecticide: Grubs are easiest to control when they are young. So take preventative action in late spring through early summer with a treatment like BioAdvanced Season Long Grub Control, which is great to use all season long.
• Monitor: During this stage, it’s important to watch for the emergence of adult beetles.

Stage 4: Adult (June – August)

This is when adult Japanese beetles emerge from the soil and begin feeding on the foliage and flowers of over 300 plant species, leaving behind skeletonized leaves.

Adult Japanese beetles are quite distinctive once you know what to look for. They are about 1/2 inch long and have metallic blue-green bodies with copper-colored wings. They are most active from June through August.

Actions to Take

• Hand Picking: Early in the morning, when they are less active, hand pick Japanese beetles off plants and drop them into a bucket of soapy water.
• Use an Insecticide: Try an insecticide like BioAdvanced Dual Action Rose & Flower Insect Killer. If you haven’t taken any preemptive actions and the beetles are feeding on your plants, products such as this one are most effective. They will kill on contact and provide extra protection to your plants. For an organic option that’s effective at killing beetles, use neem oil.
• Use Traps: If you opt for Japanese beetle traps, place them far away from the garden plants you’re trying to protect to lure the beetles away.

Stage 5: Egg (July – September)

The adult beetle continues to feed, mate, and lay eggs in the soil and turf until up to 60 eggs are laid, starting the cycle over again.

Actions to Take

• Reduce Watering: Japanese beetles prefer moist soil for egg laying. So keep the soil drier to dissuade them from laying eggs.
• Use an Insecticide: Starting in August, it’s a good idea to bring the BioAdvanced 24 Hour Grub Killer Plus back out. Lawns already under attack by grubs are best treated in early fall, and applying this product will give you fast results.

Stage 6: Feeding Larva (August – October)

The eggs hatch into grubs, which feed heavily on organic matter in the soil, including grass roots. This happens throughout the late summer and early fall, causing extensive damage.

Actions to Take

• Apply Milky Spore: Staying consistent with this treatment can keep beetle larvae at bay.
• Use an Insecticide: Remember that there are products like the BioAdvanced Season Long Grub Control, which are good for all-season use. Grubs are easiest to control when they are young, so take preventative action.
• Monitor: Keep an eye on your lawn’s health, and apply treatments as needed.

Managing Japanese beetles and grubs is a cycle of vigilance and timely action. By understanding the lifecycle of these pests and using the appropriate strategies for each stage, you can protect your garden and lawn from damage.

Remember, the key to effective pest management is persistence and consistency. Take action today to enjoy a healthier garden tomorrow.

For more how-to guides like this one, check out our other Outdoor Maintenance articles.