How do I treat for grubs in my lawn?
After fertilizer and grass seed, grub control products are typically the most prominently displayed and commonly stocked lawn care product at garden centers. For many homeowners, grub control products are an important part of the annual lawn care routine.
More often than not, people are surprised at how much there is to learn about grubs, and how many misconceptions there are about them and the damage they can do to lawns. This blog, accompanying a live video we produced in the field, addresses some of the common questions we get at the UNH Extension Infoline about grubs.
How bad are grubs for the lawn?
Grubs, which are the larval, or immature, stage of several species of beetles and chafers, can damage a lawn by feeding on the roots of your grass. Healthier grass can tolerate more grub feeding, and all grass can tolerate some grub feeding.
A grub infestation will cause patches of thinning turf, and these patches will gradually increase in size. Often times grub damaged grass will pull out very easily at the roots.
What we often hear from homeowners is that they believe they have grubs because animals like moles, skunks, crows and racoons are digging in the lawn. This isn’t a reliable clue, however, because grub infestations aren’t always accompanied by animal damage and animal damage doesn’t always result from a grub infestation. These animals feed on other insects in the lawn, like earthworms, which are beneficial to the health of the lawn. That all said, if you do have grubs and animals are digging for them in the lawn, that can be detrimental to the health of your turf and to the appearance of your yard.
How do I know if I have grubs?
Many lawn issues that resemble grub damage can be caused by something else, including disease, drought stress, hairy chinch bugs, sod webworms, shade, compaction, and more. In the early spring, for example, many homeowners suspect grub damage because of the condition of their lawn after snow melt.
The only way to be sure that you have grubs is to scout for them in your lawn.
- Using a shovel or a lawn edger, you can make a cut in a one-foot section of your lawn where you suspect grub activity.
- Peel up a one square-foot section of grass and soil from that cut. If there is significant grub damage, the grass should peel up quite easily.
- Sift around in the soil, simply counting how many grubs you find. If you count 10 or more grubs per square foot, you have a serious infestation. Finding a few grubs is normal and not cause for concern.
- Replace the grass you’ve cut in short order to avoid any damage to the lawn.
Depending on the size of your lawn, you may want to scout for grubs in several places in the lawn. Just because there are a lot of grubs, or not a lot of grubs, in a particular square foot doesn’t mean that the entire lawn either does or doesn’t have a grub infestation. You can focus your scouting on areas of the lawn that are showing symptoms of grub feeding.
As you’re scouting for grubs in your lawn, take notes so you remember which areas of your lawn have high counts and which don’t. This is important if and when you decide to treat the lawn.
Do I need to treat for grubs?
If you have a very high concentration of grubs – 10 or more grubs per square foot – treatment may be necessary to maintain healthy grass. However, if you have a lower count of grubs, yet aren’t seeing good results in your lawn, that’s a clue that you should revisit your lawn care practices more broadly.
Some of the best practices we recommend are:
- Testing your soil every 2-3 years, and following the fertilizer and amendment recommendations.
- Keeping grass mowed high – at least 2”, and ideally 3” or more – which means that your grass will have a deeper, healthier root system that can tolerate more sub-surface insect feeding.
- Over-seeding bare or sparse areas in the spring or fall (preferred).
Are there natural treatments for grub infestations?
The two natural products we are asked about most are milky spore and nematodes.
Milky spore is a bacterium that is effective for controlling Japanese beetle larvae, provided the spring soils are sufficiently warm. While the research on milky spore in our region hasn’t been revisited recently, the latest research findings are that spring soils in Northern New England are too cold for milky spore to be effective. That said, there is anecdotal evidence that it has shown at least some efficacy in warmer micro-climates within southern New Hampshire. Milky spore may be worth a try if you are:
- Sure that the grubs in your lawn are the larvae of Japanese beetles (identifying grub species requires a hand-lens because the differences are very subtle)
- In a warmer microclimate within southern New Hampshire
Keep in mind that milky spore will take several years to achieve good results.
Nematodes are microscopic worms, and some species of nematodes can work very well for controlling grubs in home lawns. To successfully use nematodes for grub control, you should keep the following principles in mind:
- The lawn needs to be well watered and the soil can’t go dry while the nematodes are getting established.
- The nematodes need to be viable (living) when applied. Purchasing nematodes from a reputable supplier and applying them right away are important.
- You need to apply the appropriate species of nematode at the appropriate time of year.
- Nematodes are sensitive to light and can be killed within a minute if exposed to intense direct sunlight – it’s generally advised to apply them on an overcast day or in the early morning.
- Some species of nematodes only control certain species of grubs, so just like with milky spore, identifying what species of grubs you have is important. Nematodes also need to be applied when the species of grubs they control are active in the soil.
- If nematodes are being used curatively, they may need to be applied every 2 weeks until the infestation subsides. For those who use nematodes preventatively, they should be applied 2 to 3 times a season.
For home gardeners that do their homework and follow instructions carefully, nematodes can be a great natural option for controlling grubs.
What chemical products can I use to control grubs in my lawn?
If you have a severe grub infestation and want to use a chemical product to control grubs, you have a number of widely available options.
From about late April into early June, you can effectively use a product with the active ingredient chlorantraniliprole to control all species of white grubs we have in New Hampshire. This chemical also controls caterpillars such as webworms and armyworms. This product is most effective when the grub is actively feeding so applying it 2 to 3 months in advance of severe grub feeding from June to August is recommended. This ingredient is in two widely available products: GrubEx® and Roundup® For Lawns Bug Destroyer. The U.S. EPA designates this chemical as a low risk pesticide due to its low toxicity to bees and other beneficial insects.
There are several other preventative products in the neonicotinoid class of insecticides. Some examples include imidacloprid, thiamethoxam and chlothianidin. Neonicotinoids are systemic and are absorbed by the grass, killing grubs not on contact but rather when they feed on the roots of plants that have been treated. These chemicals and the products they’re in all require slightly different application timing in order to control the grubs while they’re active. Generally, these chemicals are best applied from mid-June to early August. Examples of grub control products with neonicotinoids are Merit®, Meridian® and Arena®. There are also several preventative products that include both a neonicotinoid and a pyrethroid, which provides control not only for grubs but also caterpillars, billbugs, and some other lawn insect pests.
Some products registered for controlling grubs just have a pyrethroid, such as products with the active ingredient Gamma-Cyhalothrin, commonly found in the Spectracide® Triazicide® Insect Killer For Lawns. According to research from Michigan State University, products that only contain lambda-cyhalothrin, gamma-cyhalothrin, bifenthrin, deltamethrin, cyfluthrin or permethrin do not work for grub control.
This time of year (late summer and fall), only curative products can be used to effectively control grub populations. Ingredients such as carbaryl, trichlorfon or zeta-cypermethrin are curative and work on contact with grubs. Examples of products that contain these chemicals include Sevin® and Dylox®. These products can be effective, but are broad-spectrum and have a low residual, killing beneficial insects on contact as well as lawn pests like grubs. Their effectiveness is also quite variable, with wide ranging results at as low as 20 to 25% control. These products should be watered in well, immediately after application. The later in the season these products are applied, the farther down the chemical needs to travel in the soil to contact the grubs.
In most cases, whether it’s early spring or fall, it’s preferable to simply wait until the next appropriate window for using a preventative product that gets better results and is more targeted. Learn more about current insecticide approaches for white grubs from UMass Extension.
How can I control grubs while protecting bees and other pollinators?
Before applying any insecticides, the lawn should be mowed prior to application so there aren’t weeds flowering in the lawn while the product is being applied.
Also be conscious of drift. If it’s windy and you spray an area of your lawn, there’s a chance the product could drift onto flowering plants nearby. Likewise, if you’re using a spreader for a granular product, ensure you limit your application to lawn areas that have been mowed and do have a grub infestation.
There’s little reason to apply any of these products to your entire lawn if only a section of the lawn has a grub infestation. Only use chemicals to control grubs if necessary, and always follow all instructions on the label.
How can I control grubs in my garden beds?
The products that are designed to be used for grubs in the lawn are not designed for use in gardens. Rather, techniques like crop rotation, tilling, and handpicking are better options.
Will controlling grubs in my lawn help control the garden beetles that eat my plants?
Not necessarily, because the adult stage of grubs are flying beetles that can travel to your garden from outside your property. Learn more about these beetles.
Disclaimer: The use of specific brand or trade names in this article is for educational purposes only. The University of New Hampshire does not support the use of one product over others of similar composition, nor does it guarantee the efficacy or quality of any product. The user is responsible for applying pesticides only as directed on the label and in compliance with the law. Product availability is subject to change depending on registration status in the State of New Hampshire and other factors.
Got questions? The Ask UNH Extension Infoline offers practical help finding answers for your home, yard, and garden questions. Call toll free at 1-877-398-4769, Monday to Friday, 9 a.m. to 2 p.m., or e-mail us at email@example.com.
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