GRUB TREATMENT FOR A LAWN
How Common are White Grubs in Lawns in Colorado?
As summer temperatures continue to increase yearly and more lawns are watered with automatic irrigation systems, conditions have become favorable for Japanese beetles to thrive. Here’s how this occurs:
Grub damage to Colorado lawns typically becomes noticeable in September and October. However, when an infestation occurs, we can trace the problem back to July, when adult beetles lay their eggs in the soil. These adult beetles specifically choose moist or wet soil for egg-laying, as the eggs can become unviable if the soil dries out for as little as 24 to 48 hours.
Without irrigation, the heat and dryness of a typical Colorado July would cause most lawns to turn brown. However, many homeowners now utilize irrigation systems and choose to water their lawns seven days a week during July. This excessive watering keeps lawns green but also creates an ideal environment for grub eggs to thrive.
Before we discuss the best methods for controlling Japanese beetles, it’s crucial to understand their lifecycle:
- Egg Stage (July-August): Females lay eggs in moist, well-irrigated soil, often in grassy areas. The eggs hatch in about two weeks.
- Larva (Grub) Stage (September/October and again in April/May): The larvae, known as grubs, are C-shaped, white, with brown heads. They feed on the roots of grass and other plants, leading to brown, dead patches on lawns. Grubs overwinter in the soil and resume feeding in the spring as temperatures warm.
- Pupa Stage (Late May – June): After completing their larval development, grubs pupate in the soil and transition into adults over several weeks.
- Adult Stage (June/July and, in some years, early August): Adult beetles emerge in late spring or early summer and feed on plant foliage and flowers in large groups. Their activity peaks in July, and they live for 30 to 45 days, during which females lay eggs, continuing the cycle.
What is the Best Way to Control Grubs in a Lawn Without Chemicals?
The best way to prevent grub infestations in lawns is to allow the soil to dry out completely for 24 to 48 hours during July. Homeowners can effectively reduce grub issues by following the 1-2-3-2-1 lawn watering technique. This method involves watering the lawn a maximum of three days a week, typically on Monday, Wednesday, and Friday, or Tuesday, Thursday, and Saturday. This schedule provides the lawn with consecutive days without any irrigation. It’s important to avoid watering every other day, as this does not allow the soil enough time to dry out. These two consecutive days without irrigation are crucial, as they help dry out the soil and eliminate the viability of the grub eggs laid there.
Unfortunately, many homeowners continue to water their lawns seven days a week, which not only wastes water but also creates perfect conditions for Japanese beetles to lay their eggs.
Historically, grubs have not posed a significant issue for Colorado lawns until recently. From 1997 to 2020, Organo-Lawn handled only 75 confirmed cases of white grubs. However, since 2020, there has been an exponential increase in these cases, which we believe is directly linked to the rising number of homeowners using underground irrigation and improperly programmed sprinkler systems. Organo-Lawn now treats approximately 200 to 500 white grub cases annually, and we even recommend preventative insecticide treatments in August for homeowners who want to mitigate the risk of losing major sections of their lawn to grub damage.
Grub Management for Lawns
Why do organically treated lawns rarely suffer damage from lawn grubs?
There are two main reasons why lawns treated organically by Organo-Lawn rarely suffer from grub infestations.
First, Organo-Lawn insists that all its customers should follow a specific watering schedule for their lawns called the 1-2-3-2-1 technique. This watering practice gives the lawn two consecutive days without watering which allows the soil to completely dry out. When the soil is dry the grubs typically do not lay eggs in soils that are not moist or wet.
Second, Organo-Lawn’s lawn care programs are designed to promote healthy soil that supports beneficial bacteria and nematodes. One such beneficial bacterium, Bacillus popillae-Dutky, is particularly effective at killing grub larvae. By building a thriving ecosystem in the soil, Organo-Lawn helps ensure the presence of Bacillus popillae-Dutky, which in turn protects the lawn from grub problems.
How to Kill Grubs In a Lawn if an Infestation is Happening?
If you are one of the unlucky homeowners and your lawn is damaged by grubs, Organo-Lawn recommends a special insecticide treatment called Acelepryn. This grub control is not organic but it is on the EPA’s reduced risk list.
Including the lawn grub treatment Acelepryn, we always recommend an inspection of the sprinkler system to make sure the lawn is being watered according to the 1-2-3-2-1 lawn watering principals
This lawn in Boulder was attacked by white grubs. It is easy to tell if a lawn has a grub problem because the grass will pull up easily like it is a newly laid piece of sod.
Acelepryn is on the EPA’s reduced risk list and will control grubs for up to 3 months after the grub treatment has been applied to a lawn.
Acelepryn Label PDF
Acelepryn SDS PDF
What is the Life Cycle of White Grubs in a Lawn?
Illustration by K. English, NYS IPM
ADULT BEETLES EMERGE FROM THE SOIL: In late May through early July, adult Japanese beetles emerge from the ground and begin searching for food and mates. These beetles can fly up to one mile and feed on a variety of plants, with their favorites being roses, grapes, and linden trees. Younger scarab beetles are often unnoticed during this time because they do not typically attack ornamental plants.
LAYING EGGS IN THE SOIL: In July, female beetles lay up to 60 eggs each in the soil over a span of 2–3 weeks. The eggs hatch approximately two weeks later, depending on soil moisture and temperature. During this period, the white grubs are very small and primarily feed on grass roots throughout most of August.
GRUBS CAUSE THE MOST DAMAGE IN LAWNS: From late August through October, depending on external temperatures, the white grubs undergo molting stages, transitioning into second and then third-stage larvae. As they grow, these grubs consume grass roots rapidly, and lawn damage typically becomes noticeable during this time.
GRUBS DIG 3+ FEET DEEP INTO THE SOIL TO OVERWINTER: As temperatures drop in autumn, lawn grubs burrow deeper into the soil, where they will overwinter below the frost line.
GRUBS RETURN TO THE SURFACE AND HAVE A SHORT FEEDING PERIOD: In the spring, usually by late April or early May, the lawn grubs move back up to the shallow soil to feed on grass roots for a brief period. Most of the lawn damage observed in the spring is a result of their feeding in the previous fall, rather than spring feeding.
GRUBS CHANGE TO BEETLES: In late spring, the white grubs stop feeding and transform into pupae, entering a stage where they are resistant to chemical insecticides. By late June or early July, the beetles emerge from the pupae and crawl out of the soil, completing their life cycle.
How to Identify Grub Damage in Lawns?
Identifying the symptoms of lawn grub damage is relatively straightforward, making it easy for even non-professionals to recognize. The simplest method is to examine the affected area of the lawn by gently tugging on the green grass adjacent to the damaged section. If the grass pulls up easily, like a fresh roll of sod, it indicates damage. This is because grubs feed on the grass roots at or just below the soil surface.
Once you confirm that grub damage is present and the grass roots have been consumed, carefully sift through the top inch of soil until you find a white grub. If you discover grubs, it’s clear they are responsible for the damage. However, if no grubs are found, the lawn may be experiencing other issues, such as drought stress or damage from spider mites.
White grubs have traditionally been uncommon in the Front Range of Colorado. From 1997 to 2020, Organo-Lawn treated only 75 instances of grub damage in local lawns. The highest incidence occurred in 2015, with 25 cases reported due to irrigation practices and increased rainfall during the egg stage in 2014 and the spring of 2015. Another significant year for grub activity in Colorado was 2018, with about 20 reported cases. Since 2020, grub infestations have increased dramatically, and Organo-Lawn now treats between 200 and 500 grub infestations each year. Unfortunately, it appears that Japanese beetles and grubs are becoming a major concern for the Front Range of Colorado.
Click on Image to Enlarge
Professional Lawn Care Companies
We understand that insect controls can be confusing. If you have any questions about the Japanese beetle grubs or if you want to talk with a lawn care expert please contact our office to answer your tree care questions. Learn More About the Other Insects that Affect Lawns.
Organo-Lawn of Boulder (303) 499-2000 or Fort Collins (970) 225-9425
What Does Grub Damage in a Lawn Look Like?
FAQ – Is a Preventative Insecticide Grub Treatment Necessary for Colorado Lawns?
How to treat lawn grubs without using chemicals?
Taking control of lawn grubs can be simple and chemical-free by allowing the soil to dry out during July. Japanese beetles lay their eggs in lawns from late June to early July, and these white grub eggs are highly sensitive to a lack of moisture. Just one or two days of dry conditions can effectively kill the grub eggs. By turning off your sprinkler system for about a week in July during the egg laying period, you can eliminate the eggs’ viability. While the lawn may turn brown temporarily, it will bounce back swiftly with three deep waterings over three consecutive days.
If you follow the 1-2-3-2-1 lawn watering technique, your lawn will have sufficient time to dry out between watering sessions, further enhancing its resilience. Additionally, remember that grubs can be targeted by beneficial bacteria such as Bacillus thuringiensis and protozoa like Ovavesicula popilliae. By nurturing a living soil rich in microorganisms, you can create an environment that naturally combats these pests. With these strategies, you can maintain a healthy, vibrant lawn while steering clear of harmful chemicals.
What is an Effective but Safer Grub Control?
Until recently, grubs have not posed a significant issue for Colorado lawns. However, since 2020, there has been an exponential increase in these cases, which we believe is directly linked to the rising number of homeowners using underground irrigation and improperly programmed sprinkler systems. Organo-Lawn now treats approximately 200 to 500 white grub cases annually, and we are even recommending insecticide treatments using an insecticide called Acelepryn in August for homeowners who are not willing to take the risk in losing sections of their lawn to grub damage.
