LAWN GRUBS
How Common are White Grubs in Lawns in Colorado?
Very Problematic in Colorado
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.
July is The Key to Grub Control
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: Without irrigation, the heat and dryness of a typical Colorado July would cause most lawns to dry up and turn brown.
Severe Grub Damage
Grubs in a Lawn
Why are the Sprinklers Systems to Blame for Grub Infestations?
However, most homeowners now utilize irrigation systems and choose to water their lawns excessively (some even water seven days a week) during July. This excessive watering keeps lawns green, but it also keeps the soil moist. Moisture is what grub eggs need to survive, because if they go even as little as 48 hours without moisture they will dry up and die. The improper lawn watering technique of daily watering creates a perfect environment for grub eggs to thrive.
Before we discuss the best methods for controlling Japanese beetles, it’s crucial to understand their lifecycle.
Lifecycle of Lawn Grubs
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.
Illustration by K. English, NYS IPM
How to Kill Grub Eggs Using Your Sprinkler System
Dry July!
You read that correctly: you can effectively kill grubs by watering your lawn properly. Here’s how it works: grubs lay their eggs in moist soil, and if the soil dries out for even just 24 hours, the eggs will perish and become unviable.
Every-Other-Day Watering is Wrong!
The 1-2-3-2-1 lawn watering technique involves skipping watering on two consecutive days every weed during the month of July. This watering technique is specifically designed to aligns with the time grubs are laying their eggs. This method is based on logical reasoning and scientific principles, and the two consecutive days without watering are essential for reducing grub pressure. When a soil completely dries out this alone can successfully destroy the grub eggs.
Lawn Watering Can Stop Grubs
Daily Watering Keeps Grub Eggs Alive
Many homeowners still water their lawns seven days a week, which not only wastes water but also provides ideal conditions for Japanese beetles to lay their eggs. In fact, watering a lawn every other day does not allow enough time for the soil to dry out and can fail to kill off grub eggs.
When Necessary Apply This Insecticide
Due to the rapid increase of grub pressure in Colorado lawns we do suggest a preventative insect treatment of Acelapryn during the month of August. This is a fail safe way to protect your lawn and avoid potential damage. Taking proactive steps can save you from losing significant areas of your lawn to grub infestations.
July is Egg Laying Season
Grub Control for Colorado Lawns
How to Identify Grub Damage in Lawns?
The Pull Test
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.
Look for Grubs
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.
Checking for Grubs
Grub Management for Lawns
Why do Organically Treated Lawns Rarely Suffer from Grub Damage?
There are two main reasons why lawns treated organically by Organo-Lawn rarely suffer from grub infestations.
We Water a Lawn Correctly
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.
Beneficial Bacteria Kill Grub Larvae
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.
Grub Damage to a Lawn
Which Insecticide Do We Recommend for Grub Attacks?
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.
Recommend a Sprinkler Audit
In addition to the lawn grub treatment of 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
EPA's Reduced Risk Listed
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
We Can Fix Your Lawn Grub Problem!
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?
Size of a Grub
Grub Damage to a Lawn
Severe Grub Damage
Lawn Grubs - FAQs
How to Prevent 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.
Learn the 1-2-3-2-1 Lawn Watering Technique
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.
