Defeating Grubs & Saving Your Lawn

japanese beetle life cycleGrubs are public enemy #1 when it comes to insects that damage your lawn.  They can destroy large portions of healthy lawns in a matter of days or weeks.   They are the larvae of different kinds of beetles, including Japanese and Masked Chafer Beetles. They feed on grass roots killing the grass in patches. White grubs become active when the soil warms up, and they destroy lawns from late spring to early fall.

So how can you protect your lawn from these damaging insects? In this blog we will cover:

  • Do You Have Grubs?
  • Prepare Your Lawn
  • Treatment & Maintenance


grub damaged lawnIt isn’t hard to tell that grubs have invaded your lawn.  But by the time you see the evidence, it may be too late.  The grass appears to wilt and turns brown in large, irregular patches. Brown areas of grass roll up smoothly like a carpet. Birds and animals (like crows, skunks, and raccoons) may be digging in the lawn. Milky white grubs from 1/8″ to 1″ long, with brown heads and three pairs of legs, lie curled in the soil.

To find out if you have a problem, peel back a square foot of turf. If you see six or more grubs, it’s time for action. You want to apply your lawn treatment when grubs are newly hatched or just before. That’s because they’re easier to control when they’re small. For most lawns in our area, season long controls should be applied after Memorial day.  Instant kill options can be used when you see adult Japanese beetles flying around – or anytime.


Classen TR-20 De-thatcher

By taking some steps to prepare your lawn before treating it, you can make it easier for the treatment to work.  That’s why it helps to mow your lawn before treatment.

Also, if you have more than half an inch of thatch, it could get in the way of the treatment. You’ll want to de-thatch your lawn first. To make quick work of that task, visit Koopman Rentals for a De-thatcher.

There are two courses of action you can take to deal with the grub issue; trapping Japanese beetles and treating your lawn for grub larvae.


bag_a_bugJapanese beetle traps release both a sex pheromone and a floral scent, and are very effective in attracting adult beetles. They fly to the trap in droves, where they crawl or fall into the bag and can’t get out. You simply dispose of the bag, and put on a fresh one, and the process starts all over again. They work best if you have a very small, isolated population of beetles that can easily be lured and controlled by the trap.

Adult beetles are most active during June, July, and August. Traps are only effective when the adults are out, particularly during the early season before they’ve done too much mating and egg-laying.

Here are some tips to follow when using these traps:

  • Keep a Distance: Place the traps as far away as possible from the plants you’re trying to protect.
  • Install Downwind: Make sure to hang the traps downwind from your garden, so that as the beetles follow the wafting scent from the trap, they won’t be flying right over your garden and be tempted to stop for a munch.
  • Keep Traps Fresh: Not only can the lures go stale, but the bag full of dead bugs can cause the trap to stop working. Replace the lure according to package instructions, and replace the trap bag every few days.


There are two different types of grub control you can apply to your lawn; a 24 hour treatment and a long-term treatment.

24 Hour Treatment

Bayer 24 hour grubThe Bayer 24 Hour Grub Killer Plus® that Koopman carries is the product to apply if your lawn is currently experiencing a grub problem.  It is an excellent turf rescue formula that delivers overnight results. Bayer recommends applying it as soon as grubs or damage appear.

The maximum number of 24 Grub Killer Plus® applications in a year is three.  Do NOT make more than one application in any 7-day period.

Apply your grub control to a dry lawn with a rotary spreader. Make sure to follow the spreader settings provided on the product’s packaging.

After applying, thoroughly water the treated areas to activate the control and soak it into the soil where the grubs live. To prevent runoff, make sure to sweep any granules that landed on any hard surfaces back into the lawn.

Your lawn can be safely mowed once the granules have soaked into the soil.

Long-Term Treatment

Koopman carries two different kinds of long-term treatments for grubs; Grubex® , Jonathan Green Grub & Insect Control, and  Milky Spore.

Grubex and Jonathan Green Grub & Insect Control

grubex JG 2w1h

Grubex and Jonathan Green Grub & Insect Control use a targeted pesticide to kill grubs while they are young and before they can cause damage to your turf. They kill grubs for up to 4 months, but when used as directed it does not present a hazard to humans or domestic animals. The maximum number of Grubex applications is one per year. Jonathan Green Grub & Insect Control can be applied up to 3 times per year.

Apply your grub control to a dry lawn with a rotary spreader. Make sure to follow the spreader settings provided on the product’s packaging. After applying, you may lightly water the treated areas to activate the control and soak it into the soil where the grubs live. To prevent runoff, make sure to sweep any granules that landed on any hard surfaces back into the lawn.

These season-long systemic controls work when the grass root absorb the control agent and then the grubs eat the grass root and die.  For this process to work, the control must be in the plant when the grub feeds, so the best time to apply is late May/early June, so the plant has the time to absorb the control before the grub eats it.  Apply too soon, and all the power is gone before the grubs start feeding.

Milky Spore

Originally developed by the USDA, Milky Spore is a natural bacteria specifically designed to target grubs. After being applied, it will remain dormant until grubs begin feeding on grass roots and ingest the bacteria. Once grubs are infected, they will multiply the bacterium by several billion times and spread it further. After about a week the grub will die. As the grub decomposes it will release all of those billions of spores back into the soil. The spores will again become dormant until more grubs come along and repeat the cycle.

Milky_Spore_9088733Milky Spore is safe to use along with other herbicides and fertilizers and it is harmless to birds, bees, and fish. Using around pools or ponds is safe.

Apply Milky Spore with a drop spreader any time that the ground is not frozen. Make parallel passes across the area being treated, walking at a steady pace to ensure even distribution of the treatment. Then lightly water the lawn within 24 hours after application. For best results, apply in the spring, summer and fall (Memorial Day, July 4th, Labor Day) for two consecutive years.  Koopman Lumber now carries a one-time application of Milky Spore that stays active in the soil for years after one application.  See stores for details.

The final type of grub control is the 24 Hour Bayer grub killer.  Contrary to the season-long coverage, it works instantly killing grubs on contact, and then is no longer active after 24 hours.  Depending on your situation, you may need to kill the grubs now and apply a season-long control at the same time because they work very differently.

Japanese beetle hanging traps are also an excellent way to cut down the population.  Because the beetles will lay larvae that will turn into grubs that will eat the roots of your grass, it’s always a good idea to eliminate grubs at all life cycle stages.


Grubs are a formidable opponent, but with some knowledge of their life cycle and the right treatments, you can gain the upper hand and take back your lawn. At Koopman, we can help you arm yourself with the information and supplies you will need. Stop in and see us at any of our conveniently located stores, and we are always available online at www.koopmanlumber.com.

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