When to Apply Grub Control (Best Month to Kill Grubs)

Grubs are highly destructive to lawns and gardens. They feed on the roots of the grass and other organic matter in the soil, resulting in dead patches in your turf. Applying grub killers and preventers is the only way to stop the occasional grab damage. So when should you apply grub control?

The best time to apply grub control is when they are highly active. Treat lawn for grubs in early spring (late March to late April) or in late summer (around the third week of August).

When to Apply Grub Control

Relying on signs of grubs in the lawn is not enough to stage an effective control treatment. Understanding the life cycle of beetles will provide insights into the best time to treat grubs.

Common white C-shaped grubs are larvae of several different beetle species including Chafer and Japanese beetles.

Life Cycle of a Beetle

The majority of adult beetle species lay eggs in the summer and in 10 days the grubs hatch. From around August, the new grubs will start feeding on organic matter in the soil including the roots of the grass until late October when the cold weather arrives.

The grubs will then burrow 2 to 8 inches into the soil to overwinter.

When spring arrives and the soil warms, the fully grown grubs begin feeding on the grass roots again. In late spring and early summer, grubs pupate waiting to emerge as adult beetles in mid-summer. These adult beetles will lay eggs again and the cycle continues like that.

Therefore, the best time to apply grub control is early spring (late March to late April) or late summer when grubs are more active in your lawn.

How to Control Grubs in your Lawn

There are two main approaches for controlling grubs in lawns; preventive grub control and curative grub treatment which involve the use of a chemical pesticide. Further, you may opt for a natural grub control strategy which is friendly to the environment but the approach takes a longer time to get rid of grubs.

Preventive Grub Treatments

Grub preventive treatment should be applied in the spring to kill the overwintering grubs or in summer to kill the newly hatched grubs. Effective preventive grub control products contain chlorantraniliprole, imidacloprid, thiamethoxam, or clothianidin ingredients.

Examples include Scotts Grub-Ex – Granular, Bayer Advanced Season-Long Grub Control – Granular, Premium Grub Control – Granular, and Bayer Advanced Complete Insect Killer – available in both granular and liquid attach-to-hose-bottle.

Granulated preventive insecticides are best applied using a fertilizer spreader and should be watered immediately after application. There are also formulations that are mixed with water and applied using a sprayer. What is important is to read and follow label instructions before you use your insecticide.

Insecticides contain active ingredients that can be toxic to bees and other insect pollinators. To prevent this problem, mow your lawn prior to application to remove any weed flowers that are likely to attract bumble bees, honey bees butterflies, and even birds.

You should also be careful when spraying to avoid a spray drift to nearby flowers or vegetable gardens.

Curative Grub Treatments

Grub curative insecticides contain carbaryl and trichlorfon chemicals as the main active ingredients that kill all life stages of grubs. Apply these pesticides in the fall or spring when grubs are most active.

While most products will claim instant action, it may take up to 4 weeks for them to take full control over the grub population.

Examples of effective curative pesticides for grubs include Bayer Advanced 24 hr Grub Killer Plus – Granular containing trichlorfon 9.3% and Sevin Lawn Insect Granules – Granular with carbaryl 2.0%.

As with the preventive grub control products, lawns should be mowed before applying to protect pollinators like bees and butterflies.

Do not apply any curative grub treatments in the summer as grubs stop feeding in late May to pupate. Water your lawn immediately after applying the pesticide for at least 0.5 inches of water and allow at least 24 hours before letting pets or anyone in the lawn.

Remember to wear rubber gloves and rubber boots when applying insecticides to turf grass.

Natural Grub Control

Using a chemical pesticide to control grubs will potentially kill or harm other beneficial insects and soil microorganisms such as bees and earthworms. For this reason, you may decide to get rid of grubs naturally using beneficial nematodes for grubs, milk spore, or dehydration strategy.

Grub damage on the lawn

Grubs feed on the roots of the grass and other plants which causes grass to die in patches. A large infestation can ravage the whole lawn. Grubs also attract predators such as birds, raccoons, and moles that tear up or dig holes in your lawn as they hunt for the grubs.

More grub damage in lawns will be realized in late summer after the eggs have hatched into new grubs or in spring as they wait to pupate. If you dig around the edges of the affected area and roll the turf away from the soil, you will see the white grubs.

Less than 5 grubs per square foot may not affect a well-maintained lawn – this does not indicate any need to apply a grub control treatment. However, if there are more than 5 grubs per square foot, it is very necessary to apply a grub control insecticide.

Final Thought

A large number of grubs in lawns are highly destructive and using a chemical treatment will be the fastest way to stop the problem. Preventive control is more effective as compared to a curative option of controlling grubs. Few grubs in your lawn should be managed naturally or through healthy lawn practices supported by proper mowing, fertilizing, and watering.


Leave a Comment