How and When To Control Lawn Grubs With Scotts® GrubEx®

Scotts® GrubEx® (Amazon) is a specialized product designed to eradicate the Japanese beetle larvae wreaking havoc on your lawn from beneath.

GrubEx is an extremely effective tool in the fight against Japanese beetle grubs. The key to maximal effectiveness lies in knowing when to apply GrubEx and how to apply GrubEx. It also helps prevent turf damage by killing these grubs.

Lawn GrubPin

These grubs live by gobbling up your grassroots, eventually killing your lawn. Left untreated, grubs can ruin your lawn in a single season.

Depending on your local climate, when to apply GrubEx in Massachusetts, for example, may be different from areas with milder weather.

NOTE: Scotts® GrubEx®1 Season Long Grub Killer demonstrates greater efficacy than the original GrubEx, as the application kills or eliminates 25% more grubs.

In this article, we share information to help you make the best use of this excellent season-long grub killer product and build a stronger lawn.

Related: More about Scotts GrubEx at Amazon

How Can You Tell There Are Grubs In Your Lawn?

Lawn grubs can cause significant root damage to grass by feeding on the roots. This makes the grass weak, yellow, and sometimes dead. The damage can create ugly patches and make the lawn look unhealthy.

If the grubs take hold, you won’t have any problem seeing the large swathes of dead, brown grass, but you don’t want to let it get worse.

It’s important to examine your lawn closely and frequently to spot the signs of trouble.

It’s the only way to know exactly when you should apply GrubEx.

Watch for these three signs of grubs:

Brown, Dry Spots

Brown, dry spots: Of course, during the hot summer months or in times of drought, your grass may dry out, wilt, and turn brown from lack of water, but if you see this happening during cooler, wetter months, you should suspect grubs or other subterranean pests, such as moles and voles.

Damage In Sunny Areas

Damage in sunny areas: Grubs like to be in areas where the soil is warm.

If you notice the south side of your lawn seems to be showing more signs of damage than other areas, suspect grubs.


Beetles: If you see beetles bumbling about in your grass or flying just above it in the early summer, you know they are laying eggs.

If you don’t have grubs already, you soon will!

NOTE: On the label, Scotts GrubEx is listed to help control Japanese beetle infestations and armyworms when applied during spring or early summer. The label does not list if GrubEx is effective against caterpillars.

use GrubEx insecticide to kill lawn grubsPin

When To Put GrubEx Down To Treat For Grubs?

It’s important to follow the instructions on the GrubEx packaging very closely because precision in both timing and application is essential.

Early May, June, and July is the best time to apply this product to eliminate Japanese beetle infestations.

Adhering to the GrubEx directions and applying the Scotts grub control product in early May, June, and July can eliminate Japanese beetle infestations.

Therefore, when to apply scotts grubex should be very carefully calculated. Knowing how long to water in grub killer is also crucial for the product’s efficacy.

  • Remember, the beetles lay eggs in early summer.
  • The small grubs hatch in the middle of the summer.

How does grubex work?

GrubEx works as a preventative by preventing eggs from maturing and hatching, so you want to apply it in late spring and be sure it is present in the soil through mid-summer.

One application can last for about four months.

An annual application is recommended. Learn more about Scotts GrubEx at Amazon.

GrubEx When To Apply and How Quickly Does It Work?

It’s important to understand this product does not work its pest control by killing grubs.

It works by preventing eggs from maturing, so it works as soon as eggs are present.

Getting it in place is essential before the beetles begin laying eggs.

How Should GrubEx Be Applied?

A Scotts GrubEx application involves using a rotary or drop spreader to apply the pesticide evenly over the surface of your yard. The recommended rate is 2.87 pounds per 1000 square feet.

Remember when applying to dry lawns.

  • Follow up by giving your lawn a good watering to activate the product.
  • Water for about half an hour or about half an inch deep.
  • Keep pets and kids off the turf until the water has soaked in completely and the grass is dry.

Now, you might ask, But can i apply grubex to a wet lawn?

It is generally recommended to apply Grubex to a dry lawn and irrigate afterward. Applying it to a wet lawn may reduce its effectiveness.

Grubex Application Time: Can GrubEx Be Applied In The Fall?

It’s important not to apply the product at the wrong time of year.

Fall application is not recommended since the product will no longer be effective in the early spring.

Scotts GrubEx pesticide package with lawn imagery.Pin
Photo Credit: Instagram @the_grubbsfather

Additionally, you should avoid applying it when heavy rain is expected, as this will naturally wash away and dilute the product.

This could negatively impact its effectiveness.

How Do I Reseed My Lawn After Grub Damage?

If you already have severe grub damage to your lawn, it’s a good idea to remove the grass and either put in new sod or reseed the entire lawn before your first single application of Grub Ex.

If you only have small areas of damage, laying sod is preferable to seeding.

GrubEx Best Practices: Can I Apply GrubEx And Fertilizer At The Same Time?

GrubEx and fertilizer applications should be done separately. It’s better to apply fertilizer when you reseed your lawn or put down new sod and make the application of GrubEx separately.

Do lawn repair and fertilizing either in the autumn or in the early springtime.

Follow these steps:

  • Use a rake to remove dead grass.
  • For a very thick thatch, scrape it off with a spade.
  • Compost or otherwise dispose of the dead grass.
  • Use an aerator to loosen and aerate the soil.
  • Be sure to get the whole area by walking the machine across your lawn like a mower.
  • Good aeration will help your subsequent application of GrubEx to soak in better.
  • Choose your grass seed carefully to be sure it matches your existing lawn.
  • Follow packaging scotts grubex instructions to broadcast the right amount of seed to cover your square footage correctly.
  • Broadcast the seed over the damaged areas and rake lightly to incorporate it into the surface of the soil.
  • Toss out straw lightly to help keep the seed in place and protect it against birds.
  • Water deeply, and be sure to keep the soil moist until the grass has sprouted and become established.
  • Gradually cut off watering as the grass matures.
  • When it is 6″ inches high, walk on and mow it.
  • Once the grass has matured, you’ll want to apply some fertilizer.
  • If it’s late spring, apply GrubEx at the same time if you wish.
  • Be sure to use straight fertilizer containing no other ingredients.
  • Do this just before a scheduled watering.

Follow the packaging instructions to get the right amount of each product.

Use a drop spreader, and be sure to cover the entire lawn.

Remember to water after applying fertilizer and/or GrubEx.

Is Grub Control Necessary Every Year?

Grub control is necessary every year. Even if you’ve eradicated all of the Japanese beetle grubs one year, they could easily return the next year. Therefore, GrubEx should be incorporated into your annual lawn care routine.

It just takes one or two Japanese beetles to lay lots of eggs and produce lots of grubs.

GrubEx does not have a repellent effect on the beetles, so your best bet is to make the application of this product part of your annual lawn care routine.

Is GrubEx Safe For Vegetable Gardens?

This product is for lawn care only. The label is the law.

Follow the GrubEx instructions for application and timing to effectively rid your lawn of pests. Beware – if you’re wondering you can apply too much GrubEx, the answer is yes. Over-application can harm beneficial insects. Always read and follow packaging instructions closely.

Use of GrubEx for anything other than lawn care is a violation of federal law.

GrubEx Is The Best Choice For Japanese Beetle Grub Control

GrubEx is the best defense against the Japanese beetle grubs. Many grub treatment methods and pesticides (Milky Spores) will kill grubs. But GrubEx does it without harming beneficial insects.

If you follow the Grubex application instructions, you won’t have to apply the product more than once annually. Take the time to understand when to use GrubEx.

  • Timing is everything when deciding when to apply grub control.
  • The best time to apply GrubEx is early May, June, and July.
  • Is GrubEx necessary every year? The answer is yes! Annual application preventively controls any resurgence of infestation.

Make a habit of an annual, preemptive GrubEx application a part of your gardening routine to ensure a lush, Japanese beetle grub free lawn.

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