White Grubs / Lawn Grubs

Due to the hot and dry summer months and low humidity insect damage from white grubs is not very common in the Boulder and Fort Collins areas. Like most common lawn care problems, the prevention of insect pressure like white grubs can be prevented by following proper cultural practices, especially regarding proper lawn watering.

How Problematic are White Grubs in Colorado?

A white grub is the immature (larval) form of a scarab beetle, such as a European chafer or Japanese beetle. Grubs live in the soil, feeding on plant roots, so damage caused by grubs may not be noticeable until after severe damage becomes prevalent.

Due to our hot and dry climate in the Boulder, Fort Collins and Northern Front Range areas, White Grubs are not very problematic. Since 1997, Organo-Lawn has seen and treated only 25 cases of white grubs. That being said, 2015 and 2016 have been the worst years for grubs due to the wet spring and early summer rain.

Why Organo-Lawn treated lawns rarely suffer from grub infestations?

There are two reasons why lawns treated by Organo-Lawn almost never suffer from grub infestations. The main reason is because Organo-Lawn insists that all their customers water their lawns according to a very specific watering schedule.

Grub eggs die quickly if they dry out during the month of July. Organo-Lawn's watering schedule is a deep and infrequent watering which allows the soil to dry out between lawn watering. Therefore, if a lawn has grubs then we know the lawn did not dry out during the egg stage and probably was not being watered properly. Unless it rained a lot during the egg cycle if a lawn in the Boulder and Fort Collins areas are being watered properly the eggs will die.

The second reason lawns cared for by Organo-Lawn rarely have grub problems is because there is a beneficial bacteria called Bacillus popillae-Dutky that kills grubs. Organo-Lawn's lawn care programs are designed to build a living soil, that are teaming with beneficial bacteria and nematodes. If a soil is teaming with beneficial bacterial that means there will be the presence of bacteria Bacillus popillae-Dutky, which will kill the grubs.

If you are one of the unlucky homeowners and your lawn is damaged by grubs, Organo-Lawn recommends an insecticide treatment. As well as the insecticide we will recommend and inspection of the sprinkler system to make sure the lawn has proper cultural practices.

White grub lawn damage

What is the Life Cycle of Lawn Grubs

In late June and early July, the Japanese beetle adults emerge from the ground and begin to search for food and mates. Adults can fly as far as one mile and feed on a multitude of plants; their favorites include roses, grapes, and linden trees. Scarab beetles may go unnoticed at this time because they are not attacking ornamental plants.

In July, female beetles spend 2–3 weeks laying up to 60 eggs each in the soil. Depending on soil moisture and temperature, eggs hatch about 2 weeks later. During this time white grubs are very small and feed on grass roots for most of August.

From late August through October (depending on your temperatures), white grubs molt into a second and then a third stage. As they grow, white grubs consume roots very quickly. This is typically when damage to the lawn is noticeable.

As temperatures drop in autumn, lawn grubs move down in the soil. The white grubs overwinter below the frost line.

In the spring, typically late April or early May they move up in the soil to feed on roots for a very short time. Most of the lawn damage seen in the spring is a result of fall feeding, not spring feeding.

In late spring, the white grubs stop feeding and turn into pupae and are resistant to chemical insecticides. In late June or early July, beetles emerge from the pupae and crawl out of the soil, completing the life cycle.

White Grub Illustration

Illustration by K. English, NYS IPM

How to Identify the Damage Caused by White Grubs

White Grubs are not very prevalent in Boulder, Fort Collins, and the Front Range of Colorado and since 1997 Organo-Lawn has only seen 25 instances in lawns. 2015 was the worst year with 12 cases and this is due to increased rains during the egg stage in 2014 and the spring of 2015.

Identification of the symptoms of grub damage is relatively easy. When you pull on the damaged grass blades near the edge of the damaged grass areas where the grass is still green, the turf will pull up like a fresh roll of sod. The reason for this is because the grubs eat the roots of the grass within one inch of the surface of the soil. After it is clear that the grass roots have been damaged, carefully sift through the top one inch of the soil until you find a White Grub. After you have a grub in your hand, then one can conclude that the damage was caused by White Grubs.

Recommended Treatment for White Grubs in a Lawn

Preventative treatment of white grubs is easy because grub eggs are killed by dry soils during the month of July. Therefore, the first step in controlling grubs is to evaluate the lawn watering schedule and make any corrections necessary. A proper lawn watering schedule should allow the soil to dry out between watering. Grub eggs cannot survive in dry soil.

If grubs are still in their larva stage we suggest having Organo-Lawn apply a special EPA's Reduced Risk List insecticide called Acelepryn to kill any living larvae. For the Boulder and Fort Collins area we recommend an application of Acelepryn around the end of April or very early May. During this time of year is when the grubs return to feed on roots before they leave the soil. Finally, it is important to monitor the lawn and if any signs of another infestation occur then contact Organo-Lawn's office immediately.

If the grubs killed the lawn and the grass is severely damaged to the point where it cannot recover on its own, we will recommend a top seeding package to reestablish the grass in the lawn.

If you live in the Boulder or Fort Collins area and you believe that your lawn might have grubs, please contact our office to schedule a insect and disease diagnosis or to schedule a grub treatment.

Acelepryn Label and MSDS



Click on an image to enlarge the photo.

White grub next to a dime for size reference.

White grub damage found in a lawn in Boulder, Colorado.

Severe white grub damage in a lawn in Fort Collins.