When to Apply Grub Control: Best Timing to Put Down Grub Killer

Grub damage starts to occur early in the spring but becomes more intense as summer approaches. If you don’t treat for grubs by applying grub control, the same problem can easily recur every year. So, what is the best time to apply grub control on your lawn?

The best time to apply grub control is early spring (late March to late April). You can also apply a grub killer when you see signs of grub damage. Grubs turn into adult Japanese beetles from late spring to early summer, which is a good time to put down a grub preventer for the following season.

A good grub preventer should contain chlorantraniliprole, a compound that acts on the larvae of the grubs as they hatch. I use and recommend Syngenta’s Acelepryn G Insecticide for extensive infestations or Scotts GrubEx. Make sure the timing is right for the application of this insecticide for season-long grub control. More on this below.

Best Time to Apply Grub Control

Grub control comes in two types – grub preventers and grub killers. Prevention is the best approach to maintaining a healthy lawn, but when you already have signs of grub damage in your lawn, you want to apply an insecticide for immediate control.

The best time to apply grub control is early spring (April to May) to prevent grub damage that occurs in the fall. For grub killers, treat the lawn as soon as you see irregular brown patches of grass. You can also put down the treatment in the months of June and July to prevent grubs the next season.

Most grubs have a life cycle that lasts one year. Japanese beetles and European chafers turn from pupae into adult beetles during the months of summer. They lay eggs in your lawn which hatch into grub worms in the fall.

When to apply grub control

The newly hatched white grub worms remain dormant in the ground until spring when they start to feed on the roots of your turfgrass, causing brown patches of dead grass all over the lawn.

When you see your grass turning brown, check to confirm it is a grub problem and treat for grubs with a good grub killer immediately such as GrubEx.

  • Grub damage signs start to show from early spring to summer.
  • Prevention should be done a season earlier.
  • Treat for grub damage by putting down grub killer when you see patches of dead grass.

Early summer, adult beetles emerge from the soil when the cycle is complete. They lay eggs in the lawn, which hatch within two weeks. At this time, the newly-hatched grubs start to cause damage to your lawn until when the temperatures drop in the winter when they go dormant deep in the soil.

How often should you apply grub control?

White grub worms are the most destructive to lawns because they feed on roots, leaving the grass dead and turning brown. You’ll need to apply grub control as per the stage of infestation in your lawn. But how often should you apply grub control?

Grub control insecticides can be applied up to 2 to 3 times per year depending on the season and stage in the life cycle of the grubs. Put down grub killers when you see irregular patches of dead grass, and apply preventive treatment early in spring and also during fall to eliminate the pests completely for the next couple of seasons.

In brief, you need to apply grub killer as soon as you see signs of grub damage in your lawn, and then put down a grubworm preventer to prevent grubs from damaging your lawn next season.

Signs of grub damage in lawns and when to apply grub killer

The best timing for applying a grub killer may also depend on the region. For example, common practices for Massachusetts, Iowa, Texas, New Jersey, Florida etc. may not be the same because the species that are prevalent in these regions may be different.

Here are the generally recommended timings for grub control for different regions:

Area/StateWhen to apply grub killer
MassachusettsApril to May
DelawareApril to May
IowaJune and July
TexasEarly June to mid-July
FloridaLate June to early September
New JerseyMid-July to August
MinnesotaMid-June to mid-July
ConnecticutEarly August
South CarolinaEarly August
KansasMid-June through early July

Do I need to apply grub killer every year?

You don’t need to treat for grubs every year because a preventive pesticide application should kill a majority of the grubs that are likely to cause damage the next year. Grubs in your neighbor’s lawn are unlikely to spread to your lawn every year, so only treat when you see the signs of grub damage.

In fact, a healthy lawn can tolerate a few grubs here and there without showing any signs of damage. You only need to start treating the lawn with a grub killer when you see irregular patches of dead grass and also put down a grub preventer as a precaution for the next year.

For prevention purposes, put down lawn insecticides with either thiamethoxam, imidacloprid, or chlorantraniliprole as the active ingredients once every 2 years early in the spring. Follow the instructions on the product label to guide you on the right time to apply the grub control pesticide because some products last longer in the soil than others.

When is it too late to treat for grubs?

It is too late to treat for grubs in late summer (September) because white grubs will have turned into adult beetles that are hard to kill. Even spraying a grub killer on the lawn may not kill 60% of the beetles that are already feeding on the foliage and laying eggs in your lawn.

However, it will only be too late to put down a grub killer pesticide when the grass is already dead because you’ll not be able to revive the grass that’s been dead for more than 5 weeks.

Apply the grub killer when the grubs are actively causing damage to your lawn. It won’t take any timing to do that. The application that needs precise timing is that of a grub preventer because it needs to be in the soil before or when the eggs hatch into larvae (white grub worms).

Can you apply GrubEx before it rains?

GrubEx is best applied before it rains because the water from the downpour will wash the insecticide into the soil. Grubs live about 2 inches into the soil and this is where you need the treatment to reach.

The best practice is to put down grub control granules or dust and then water down the lawn to ensure the treatment enters the root zone and kills grubs that are cutting the roots of your grass.

You can also time to apply the grub killer just before it rains, but first, make sure it is forecast to rain in your area in the next few hours.

Pro tip:

I recommend mowing first before applying GrubEx or any other grub killer to ensure most of the pesticide penetrates down into the soil to kill grubs that are damaging your grass.

How long do grub killer insecticides last?

Most grub preventers last between 60 and 90 days in the soil, which means they can control grub worms from the time they hatch to the time they become larvae. However, different products may have varying half-lives so it is important to do the timing properly before putting them down for the most prolonged control of grubs.

For example, Syngenta’s Acelepryn insecticide can take 3-4 weeks to penetrate thatch in your lawn and enter the root zone where there’s grub worm activity, Once it enters this zone, it can kill grubs and offer season-long control of these pests with just a single application.


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