Don’t Let the Grubs Bug You: A Guide to Healthy Turf

beetle grubs laying in a hand — Beetle grubs are the larval form of beetles. They can damage plants, but not in all cases and are important parts of the ecosystem. Photo by Amanda Bratcher

May 1st marks the official kickoff for the warm-season grass cycle in North Carolina. As homeowners head outside for garden renovations and spring digging, it’s almost inevitable that a shovel full of soil will turn up a few grubs. While many people call the office in a panic when they see these critters, I’m here to tell you: it’s usually not as bad as it seems!

Let’s take a moment to reflect on what grubs are, why they are in your yard, and—most importantly—when you should (and shouldn't) try to control them.

What Exactly is a Grub?

Grubs are the larval (immature) form of beetles. Think of them as the “caterpillars” of beetles! While most people immediately think of the invasive Japanese beetle, there are more than 400,000 species of beetles worldwide, with tens of thousands in North America alone.

These larvae live in various habitats and perform critical ecosystem functions, including acting as a vital food source for birds and other wildlife. While some species do eat grass roots, a healthy, well-maintained lawn can easily overcome minor root pruning without you ever noticing.

Debunking the "Mole Myth"

One of the most common misunderstandings in the gardening world is that "grubs bring moles."

Research has clearly shown that while grubs are a small part of a mole’s diet, moles actually prefer earthworms. Ironically, many homeowners rejoice when they see earthworms but fret when they see grubs, when in reality, if you want fewer moles, you'd have to get rid of your "good" worms! Since we want those worms for soil aeration, the best approach is to manage the turf, not the tunnels.

turf area with insect damage — Grubs can chew on roots, making turf seem weak and brown. This is a symptom of unhealthy turf. Photo by N. Bosold, Penn State (retired)

The Best Defense is a Good Offense

The best way to manage grubs is to start with a healthy, resilient lawn. If your turf is thriving, a few grubs won't cause irreparable damage.

Start with a Soil Test

Before you buy any treatments, perform a soil test. This tells you exactly what fertility and pH levels your specific turf species needs to stay strong. Soil testing is available year-round through the NCDA&CS Soil Testing Lab and it’s FREE from April until early winter (and $5 a sample in the winter).

Stop by the Lee County Cooperative Extension office to pick up your FREE sample boxes and forms. We are happy to help you interpret the results!

Smart Irrigation

Most turf grasses struggle during droughts, making them susceptible to damage. While we recommend an irrigation system for consistency, be careful not to overwater, which can actually attract certain egg-laying beetles.

To Control or Not to Control?

If you feel your grub population has reached a "threshold" (typically more than six to ten grubs per square foot) where the grass is actually dying, you have options—but they come with caveats.

Milky Spore

This is a biological control (a bacteria, Paenibacillus popilliae) that can be effective against only Japanese beetle grubs and it requires patience. You must inoculate your entire turf area so the fungus comes in direct contact with the grubs. This requires you to properly identify the grubs (good luck!) and make sure your turf area stays inoculated. These spores work best when applied in late September or early October to soil with a pH level between 6 and 7.

Insecticides

I generally do not recommend blanket insecticide applications for grubs. It is very difficult for the average homeowner to determine whether a "grub" is the reason for landscape issues, or to distinguish a native "good" beetle larva from an invasive Japanese beetle. Our native beetles provide essential ecosystem services, and we don't want to lose them to "friendly fire."

The Bottom Line

Don't fret about finding a few grubs while you're planting your summer annuals this week. Focus on your soil health, keep your grass hydrated, and let the local ecosystem do its job.

Getting in Touch

Contact the NC Cooperative Extension Office in Lee County Amanda Bratcher is the horticulture agent with N.C. Cooperative Extension—Lee County Center. You can reach out to the office at 919-775-5624 for technical assistance with soil samples or any other garden and farm questions! Visit our website to see upcoming programs.