How to Prevent and Deal With Lawn Grubs

Lawn grubs are the larval stage of various beetles that can cause major damage to lawns by feeding on grass roots. Preventing and dealing with lawn grubs requires diligence and multiple control strategies for the best results. This comprehensive guide provides homeowners and gardeners with extensive, detailed information on identifying lawn grubs, preventing them from invading turf grass, and effective treatment methods if an infestation occurs.

What Are Lawn Grubs?

Lawn grubs are the larval form of beetles belonging to the Scarabaeidae family. The most common grub species that attack lawns in North America are:

  • Japanese beetle grubs – Popillia japonica
  • European chafer grubs – Rhizotrogus majalis
  • June beetle grubs – Phyllophaga spp.
  • Asiatic garden beetle grubs – Maladera castanea
  • Black turfgrass ataenius grubs – Ataenius spretulus
  • Masked chafer grubs – Cyclocephala spp.
  • Green June beetle grubs – Cotinis nitida

These white C-shaped grubs live underground and feed on the roots of grass. As they grow bigger, they can devour entire root systems, leading to dead patches that are easily pulled up like carpet.

Grubs pupate into adult beetles that emerge from lawns in early summer to mate and lay eggs. The eggs hatch into larvae about 10-14 days later, starting a new generation of destructive grubs.

Life Cycle of Lawn Grubs

The life cycle of common lawn grub species has four stages:

Egg – Adult beetles lay small whitish eggs in the soil from late spring to mid summer. The eggs hatch into larvae usually within 2 weeks.

Larva – The C-shaped grubs feed actively on grass roots through summer and fall, causing lawn damage. They eventually grow to about 1-1.5 inches long.

Pupa – In late fall when temperatures drop, grubs burrow deeper into the soil and enter the pupal stage. They transform into beetles within the protective cocoon.

Adult beetle – Pupae become adult beetles that emerge from lawns in spring or early summer to mate, feed, and start the cycle again by laying eggs in turf grass.

Signs of Lawn Grub Damage

Lawn grubs can rapidly destroy grass by feeding on the roots that deliver water and nutrients. Watch for these signs of a potential grub infestation:

  • Irregular dead patches – Brown areas that appear in the lawn, usually first noticed in late summer. The damaged areas feel spongy and are easily peeled back from healthy grass.
  • Sparse turf – Thinning areas of the lawn that look drought stressed, but do not respond well to increased watering.
  • Skunk or raccoon damage – Nocturnal digging by wildlife feeding on grubs exposes large sections of damaged grass. Look for upturned soil and huge rolls of grass “carpet”.
  • Unthrifty growth – Poor density and lackluster color of the grass, even in well fertilized areas. Plants lack robust root systems.
  • Flocks of birds – Watch for groups of birds like crows and seagulls that peck the ground to feed on grubs they detect below.

Carefully inspect the roots and surrounding soil of damaged areas to look for the curled white grubs. Confirm their presence before applying treatments.

When Are Lawn Grubs Most Active?

Lawn grub damage is most prevalent and visible when the larvae are actively growing and devouring grass roots through summer and fall. However, effective prevention and control requires impeccable timing.

Here are the peak activity times of problematic grub life stages in most regions:

  • Spring – Adult beetles are active and lay eggs in the soil from late spring onwards. Preventive treatments should target the eggs and newly hatched grubs.
  • Summer – Young grubs start feeding on roots through the summer. Curative treatments applied in early summer can control larvae before they cause severe damage.
  • Late summer to fall – Larger mature grubs do the most root destruction from August-September until the first hard frosts. Expect to see dead lawn patches. Curative treatments should target bigger grubs.
  • Fall & winter – Grubs burrow deeper and enter pupal stage. No treatments are effective when grubs are inactive and pupating.
  • Early spring – Adult beetles emerge and exit lawns to feed, mate, and start the cycle again. Preventive treatments should target them before egg-laying begins.

How to Prevent Lawn Grub Infestations

Preventing lawn grubs from invading turf grass is more effective than trying to get rid of them after significant lawn damage occurs. Here are smart tactics to proactively protect against grubs.

Encourage Natural Predators

Promote beneficial predatory insects, birds, mammals, and soil organisms that feed on white grubs and keep their populations in check:

  • Avoid excess use of pesticides that kill natural predators. Spot treat grub damaged areas only.
  • Introduce nematodes like Heterorhabditis bacteriophora that parasitize and kill grubs.
  • Attract birds like starlings, robins, and crows that eat grubs from lawns.
  • Entice moles, shrews, raccoons, and skunks with suitable habitat. Put up with minor digging damage for their big grub appetite.
  • Boost soil health with compost and aeration to support centipedes, ground beetles, bacteria, and fungi that all help suppress grubs.

Choose Resistant Turf Varieties

When establishing a new lawn or overseeding bare spots, select turf grass varieties that have better resistance to white grubs. Some options are:

  • Fescue grasses like Rebel Exeda and Houndog V that have endophytes that deter grubs.
  • Perennial ryegrass cultivars with improved resistance such as Accentuate, Assure II, and Barpiper.
  • Hard fescue mixes are less tasty to grubs than other cool-season grasses. Try Trevail, Reliant IV, or Nordic.
  • Zoysia, bermudagrass, and other warm-season grasses are somewhat repellent and less damaged. Empire zoysia shows tolerance.

Maintain Healthy Turf

A lush, vigorous lawn is less susceptible to white grubs. Promote healthy grass through proper mowing, fertilization, irrigation, and other care:

  • Mow high (3-4 inches) and frequently to encourage deep roots less accessible to grubs. Leave sharp clippings that deter beetles.
  • Fertilize moderately in fall with a slow-release organic source to feed the grass rather than grubs.
  • Water deeply and infrequently to promote deeper rooting. Avoid excess moisture that brings grubs closer to the surface.
  • Dethatch and aerate compacted areas so roots grow deeply in aerated soil. Fill any bare spots that invite grubs.
  • Overseed thin turf in fall to thicken growth and recover from any grub damage.

Apply Preventive Treatments

Use selective, targeted lawn products when adults are first active in spring or right before eggs hatch in early summer:

  • Adult beetle control – Apply Milky Spore (Bacillus popilliae) to lawns in spring to kill active adult beetles before they lay eggs. It infects and spreads naturally through the white grub population. Reapply annually.
  • Chafer grub control – Use a soil drench of Merit (Imidacloprid) in early summer when adults start laying eggs and young grubs soon hatch. It protects for 3 months or more.
  • Japanese beetle grub killer – Apply Arena (Clothianidin) around early-mid summer before larvae hatch and start feeding on roots. It protects all season with one application.
  • Organic grub prevention – Use Diatomaceous Earth or Nematodes like Heterorhabditis bacteriophora early in the season to kill young grubs in the soil. Both are eco-friendly options.

These selective grub-targeting treatments work well for prevention when timed properly and reduce damage from hatching larvae over the entire season.

How to Identify Lawn Grubs

Confirmatory identification is important before investing time and money in treatments. Here are the best ways to positively identify white grubs if you spot lawn damage:

  • Check roots of dying grass – Gently pull up damaged patches of lawn and look for plump, curled, C-shaped white grubs clinging to roots or in surrounding soil.
  • Dig test pits – Use a shovel or trowel to dig test pits about 4-6 inches deep in areas of suspected grub damage. Look to see if grubs are present in the soil profile and root zone.
  • Apply soapy flush – Mix few tablespoons of lemon-scented dish soap in a bucket of water. Pour this solution over 1 square foot of damaged lawn. Count any grubs that float to the surface within 5-10 minutes.
  • Set out night light – Position a flood light over a patched area of suspected grub damage and check after 1-2 hours for raccoons, skunks, or other wildlife digging for grubs attracted to the light.
  • Get samples identified – If you are unsure of the exact grub species present, place several larvae and adult beetles from lawn in a sealed plastic bag. Contact your local county extension agent to have the samples examined by a pest diagnostic clinic or expert. Proper identification ensures using the right treatments.

Finding and positively identifying active white grubs confirms they are responsible for the lawn damage before treating an infestation.

How to Get Rid of Lawn Grubs – Control & Treatment

If preventive measures fail and lawn grubs take hold, here are effective treatment options listed from most eco-friendly to strongest chemicals. Always confirm grubs are actively present before any blanket applications.

Apply Milky Spore Disease

Milky spore disease (Bacillus popilliae) is a biological grub treatment derived from beneficial bacteria that liquefy and kill Japanese beetle larvae in soil but leave other species unharmed. It remains effective at spreading and suppressing grubs for many seasons but takes longer to start working than other remedies.

Key tips for milky spore grub control:

  • Time applications for early summer when small grubs first hatch. Water in well after applying.
  • Make multiple light applications over the lawn over two weeks to establish wide coverage. Apply according to label.
  • Get milky spore formulations like Grub Attack or Top Gun specifically for Japanese beetle grubs. Choose strain V-10 of the bacteria.
  • Expect milky spore disease to keep spreading naturally through the soil and providing multi-year control.

Release Parasitic Nematodes

Beneficial parasitic roundworms called entomopathogenic nematodes offer an organic curative treatment that provides natural grub control. Look for the species Heterorhabditis bacteriophora or Steinernema glaseri ideally suited for controlling common white grubs.

Follow these guidelines for nematode applications:

  • Apply when grubs are actively feeding roughly June-September so nematodes seek them out underground as hosts.
  • Select reputable commercial nematode products like Nemasys, Exhibitline sf, or Guardian that provide millions of live worms per square foot.
  • Check product labels and calibrate irrigation system for proper dilution and application rates. Soak the lawn thoroughly.
  • Make 2-3 repeat applications spaced 1-2 weeks apart for sufficient coverage as nematodes have limited mobility in soil.
  • Nematodes require moderate soil moisture and temperature between 60-90°F to work effectively. Irrigate lawn before and after release.

Use Targeted Grub-killing Insecticides

Insecticide products containing chemicals specifically toxic to beetle grubs can provide curative grub control when applied correctly:

  • Imidacloprid – Systemic neonicotinoid insecticide with long soil activity against grubs when applied early in the season. Popular products are Merit, GrubEx, and Bayer Season-Long Grub Control.
  • Thiamethoxam – Neonicotinoid that offers the fastest grub knockdown and protection against reinfestation that season. Look for Allectus, Flagship, and GrubGone.
  • Clothianidin – Neonicotinoid grub killer similar to imidacloprid but longer control (8-10 weeks from one application). Look for Arena and Green Light Grub Control with Arena.
  • Trichlorfon – Carbamate insecticide with contact activity against sizable grubs. Available as Dylox, Proxol, Bayer Advanced 24 Hour Grub Killer and rapid grub killers.

Follow label directions carefully for correct application rates and timing. Limit use in gardens and vegetable crops. Most provide 3-4+ weeks of curative grub control with one properly timed application.

Promote Beneficial Nematodes in Soil

Boost populations of useful soil-dwelling roundworms like rhabditid and cephalobid nematodes to prey on small grubs and disrupt their lifecycles.

  • Reduce or avoid use of chemical nematicides and fumigants that kill beneficial nematodes.
  • Foster large diverse nematode populations through reduced tillage and amendments like chitin and compost.
  • Check for native nematodes in soil samples taken 4-6 inches deep where grubs feed. Identifying species mix helps select best cultural practices to promote helpful nematodes.

While predatory nematodes don’t offer quick curative control like insecticides, improving their habitat in lawns pays dividends by allowing them to suppress grub populations continually over the long-term.

How to Repair Grub Damage in Lawns

Where lawn grubs have already destroyed significant areas of turf grass, focus efforts on repairing the damage:

Rake and Reseed Dead Areas

For dead brown patches:

  • Loosen surface thatch with a metal rake to allow for seed contact with soil.
  • Sprinkle new grass seed mix evenly over damaged areas. Consider more grub-resistant varieties.
  • Cover reseeded spots with 1/8 inch layer of compost as a topdressing to retain moisture while seeds germinate.
  • Water gently daily until new grass sprouts fill in bare areas. Continue watering new seedlings regularly as they establish.

Overseed Thin Turf

For thinning or poor turf:

  • Mow, dethatch, and aerate the lawn to allow good seed-to-soil contact.
  • Overseed thin or bare areas with grass varietal matching existing lawn. Consider endophyte-enhanced seed for resistance.
  • Top dress reseeded areas with a thin layer of screened compost or vermiculite to retain moisture.
  • Gently water lawn in early morning to keep top 1 inch moist until overseed establishes. Don’t soak reseeded areas.

Replace Severely Damaged Areas

For dead areas beyond repair:

  • Remove completely dead sections of lawn down to soil level using a sod cutter, shovel or tiller.
  • Shape and smooth the surface, filling any low spots with quality topsoil as needed. Compact lightly.
  • Lay new sod pieces tightly together over prepared area for full instant coverage. Or seed bare soil heavily with a premium grass seed mix ideal for the site’s sun and soil conditions.
  • Mist sod pieces with water twice daily until the grass takes root in about 2 weeks. For seed, water daily until sprouted in 1-3 weeks based on variety. Provide light weekly fertilization.

With proper repair, grub damaged lawns can recover fully and return to their former vigor within a season. Ongoing prevention is key to avoid repeat infestations.

FAQs about Controlling Lawn Grubs

Does applying grub control early prevent damage?

Yes, effective prevention is key with white grubs. Applying treatments before grubs hatch and start feeding on roots prevents lawn damage all season long. Well-timed preventive applications in early summer provide longer protection.

What is the best organic way to get rid of grubs?

Milky spore treatment and beneficial nematodes offer organic curative grub control. Both must be applied when grubs are actively feeding for best results. Multiple light applications ensure wide coverage. For prevention, improve turf health and use resistant grass varieties.

When should I put down grub killer?

Target very early larvae by applying grub insecticides from mid-spring through early summer before damage appears. For sizable active grubs causing visible injury, apply fast-acting controls like Dylox or Allectus in late summer through early fall ideally before September. Avoid treating when grubs are dormant deep in soil over winter.

How do I repair dead spots in my lawn from grubs?

For dead patches under 6 inches wide, loosen soil and overseed with quality grass seed suited for sun/shade conditions. Cover with a thin compost layer to retain moisture and help seeds germinate. Mist gently daily. To fix larger dead areas, cut out the dead turf and replace with new sod or seed and start a new lawn from scratch.

How do I know if I have grubs in my lawn?

Indications of a grub infestation include dead patches that lift up easily, thinning turf unresponsive to water, digging animals, and flocks of birds feeding on grubs they detect below. Confirm grubs by digging up damaged areas to check for plump white C-shaped grubs on roots or inspecting larva that rise to the surface after drenching small sections with dish soap solution.

When is the best time to apply GrubEx?

Ideally apply GrubEx or other imidacloprid products from late spring through early summer before egg hatch to prevent damage. For curative control of active grubs, apply in July or August before grubs