Grub worms, also known as white grubs, are the larval form of various beetles. They are common lawn and garden pests that can cause significant damage by feeding on the roots of grass, vegetables, and ornamental plants. Controlling grub worms can be challenging, but there are several effective ways to get rid of them or prevent infestations. This article will provide an in-depth look at what kills grub worms and how to use grub control products safely and effectively.
What Are Grub Worms?
Grub worms are the immature stage of beetles belonging to the Scarabaeidae family, including Japanese beetles, June beetles, European chafers, and Oriental beetles. The adult female beetle lays eggs in the soil during late spring or summer. The eggs hatch into white C-shaped grubs with brown heads and six legs. The grubs grow quickly, molting several times over summer and reaching up to 1-1.5 inches long when fully mature.
Grub worms feed on plant roots, shredded organic matter, and decaying roots for 9-10 months before pupating into adult beetles and emerging from the soil. Their feeding can destroy lawn roots, resulting in dead patches that are easy to lift up like carpet. Vegetable gardens may be riddled with holes and wilted, dying plants due to grub damage.
Life Cycle of Grub Worms
The life cycle of grub worms has four stages:
Egg: Adult female beetles lay small, oval white or yellow eggs in the soil. June beetles and Japanese beetles may lay eggs in clusters, while other species lay eggs singly. The eggs hatch in about 2 weeks.
Larva: The larvae are white grubs with brown heads and six legs that grow up to 1-1.5 inches long. They molt and feed on roots for 9-10 months, causing the most damage in mid to late summer.
Pupa: In late summer, the grubs stop feeding and move deeper into the soil to pupate. The pupal stage lasts 1-2 weeks.
Adult beetle: Adult beetles emerge from the soil starting in mid to late summer. After feeding for several weeks, the females lay eggs to start the cycle again. There is one generation per year in most regions.
Signs of Grub Infestation
It’s important to watch for early signs of grub damage in lawns and gardens to treat infestations before they get severe. Indications of a grub problem include:
– Dead, brown patches of grass that can be lifted up like carpet
– Wilting, dying plants in vegetable gardens
– Raccoons, skunks, or birds digging and feeding in the lawn
– Grubs found while digging in the soil
– Adult beetles swarming on vegetation and mating
Skunks and raccoons digging in the lawn are a telltale sign since they dig up and feed on grubs. The grubs may also attract moles which make tunnels in search of their favorite food.
When Are Grubs Most Active?
Grub worms feed heavily during the summer months while actively growing and molting. Damage to lawns and gardens is most apparent in mid to late summer when grubs are nearly full grown (up to 1-1.5 inches long). Their feeding activity decreases in fall as the grubs start moving deeper into the soil to pupate for winter.
The adult beetles are present from mid to late summer through early fall. September and October are peak months for adult beetle activity as they swarm lawns to mate and lay eggs. Treating for grubs or adult beetles during this time can help reduce infestations for next year.
Natural Grub Control
There are several eco-friendly methods to get rid of or deter grub worms naturally without pesticides:
Introduce Beneficial Nematodes
Nematodes are microscopic organisms that occur naturally in soil. Certain species attack and kill grubs but are harmless to plants, animals, and people. Nematode products can be applied to lawns and gardens to wipe out grub populations. They are most effective against young grubs.
Encourage Natural Predators
Certain animals like birds, raccoons, moles, and skunks feed on grubs. Avoid killing them and encourage these predators to frequent your lawn or garden areas to help control grubs. Their digging may be unsightly at first, but it indicates they are feasting on the grubs.
Use Milky Spore
Milky spore is a natural bacteria that kills Japanese beetle grubs when they ingest it from the soil. It does not harm beneficial insects or earthworms. It can take 2-3 years to establish milky spore in the soil, but one application provides long-term control.
Apply Diatomaceous Earth
Diatomaceous earth is made from fossilized diatoms and has sharp edges that damage the exoskeleton of grubs. Apply as a powder over lawns or garden beds. Reapply after heavy watering.
Plant Grub-Deterring Plants
Certain plants like marigolds, chrysanthemums, geraniums, and larkspur contain chemicals that deter adult beetles from laying eggs nearby. Planting them around the garden perimeter or borders may help reduce grub populations over time.
Chemical Grub Killers
While natural control methods are ideal, chemical grub killers are sometimes needed for effective control, especially once infestations are severe. Here are some common active ingredients in grub control products:
Imidacloprid – This systemic insecticide is taken up by plant roots, making the vegetation toxic to grubs feeding on the roots. It requires adequate rainfall or irrigation to move it into the soil. Apply as early as possible in spring for preventative grub control.
Halofenozide – Halofenozide kills grubs when they ingest treated soil but does not harm beneficial insects, birds, or mammals. It is less toxic than many traditional grub treatments. Apply in spring or early summer.
Carbaryl – Carbaryl provides quick knockdown of surface feeding grubs but persistence is short. It may require repeat treatments. Avoid applying when pollinators are active.
Trichlorfon – Trichlorfon kills grubs upon contact but degrades quickly in sunlight. Reapply as needed when monitoring indicates grubs are still active.
Chlorantraniliprole – This anthranilic diamide insecticide provides long residual activity against grubs when applied to turf or soil. It binds to soil particles and releases over time when grubs ingest it.
When using chemical grub killers, always follow label directions carefully for correct timing, application rates, and watering in after application. Only use pesticides registered for use on turf and ornamentals.
When to Apply Grub Control
Timing is critical when using grub control products for best effectiveness:
Spring: Apply preventative grub treatments in spring to kill newly hatched grubs before they start damaging roots. Mid to late spring is ideal for preventative control with most grub killers.
Summer: Switch to faster acting grub killers in summer to control larger grubs actively feeding on roots. Look for dead patches appearing mid to late summer.
Fall: Use grub treatments again in early fall to kill grubs before winter as well as emerging adult beetles. September and October are peak months for adult beetle activity.
Always follow label instructions for when to apply specific grub control products. Preventative application in spring offers longer residual control through the whole grub season.
How to Apply Grub Killer Products
It is important to use grub killers correctly to get the best control:
– For liquid sprays, use a pump sprayer or hose-end sprayer for even coverage over the lawn. Apply when grass is damp but not soaked.
– Granular products can be spread with a hand spreader or pushed rotary spreader. Set the spreader on the correct setting listed on the label.
– Water in treatments lightly after application to move the product into soil. Granules work best if irrigation follows within 24 hours.
– Adhere to listed application rates and frequency. Many products require repeat treatments.
– Reapply grub killers after heavy rainfall if it occurs shortly after treatment.
– Avoid mowing turf for 1-2 days before and after application.
– Keep children and pets off treated areas until lawn is dry.
How to Prevent Grub Infestations
Preventing grub problems is more effective than trying to control existing infestations. Here are some key prevention tips:
– Maintain healthy soil with good drainage and avoid excessive thatch buildup.
– Water early in the day. Avoid overwatering lawns.
– Use grub-resistant grass seeds and turf cultivars.
– Apply milky spore and diatomaceous earth routinely as part of an IPM program.
– Use beneficial nematodes to kill grubs before damage starts.
– Manage adult beetles in summer/fall to reduce egg laying.
– Set up Japanese beetle traps in spring to capture first emerging adults.
– Encourage natural grub predators like birds and moles in the yard.
– Rotate crops in vegetable gardens; avoid planting in same spot as previous year.
Other Methods to Kill Grubs
In addition to insecticide treatments, there are some other methods that may help control grubs:
Hand Picking – Manually dig up and kill grubs in the soil. Effective for small areas. Look for dead turf patches.
Solarizing Soil – Covering moist soil with plastic in hot sunny weather kills grubs and other soil pests from heat/steam.
Parasitic Wasps – Certain wasps lay eggs inside grubs, killing them from the inside out. Attract these wasps by avoiding insecticide use.
Water Flow – Frequent, heavy water flow directed into grub damaged areas may physically displace grubs.
Natural Clay – Spreading a thin layer of kaolin clay over lawns can act as a physical barrier against adult beetles laying eggs.
Signs Treatments Are Working
It takes time for grub treatments to take effect, but here are some signs the products are working:
– Seeing dead grubs in soil when digging
– Reduction in beetles swarming on plants
– Less raccoon or skunk digging activity
– Improved turf health and regrowth
– No new brown dead spots appearing
– Sampling reveals lower grub counts over time
Be patient, as it takes 1-2 weeks for results. Persistence through the whole grub season is key for knocking down populations long-term. Combine treatments with prevention methods for best control.
Safety Tips for Grub Control
When using any pesticide, it is essential to take proper safety precautions:
– Read and follow all label directions for correct use.
– Avoid breathing in dusts or mists from products.
– Wear gloves and wash hands afterwards when handling.
– Keep children and pets off treated areas until dry.
– Use least toxic formulations when possible.
– Apply only at listed rates. More is not better.
– Do not allow runoff from treated areas into storm drains or surface water.
– Rinse empty containers and dispose according to label guidelines.
Using grub control products correctly minimizes risks to people, pets, and the environment. Integrate chemical measures with preventative methods for best results. Monitor regularly to determine if additional treatments are needed. With persistence, you can knock down those pesky white grub infestations.
Organic Grub Killers
For those wanting to avoid synthetic chemicals, there are some effective organic approaches to killing grubs:
Milky Spore (Bacillus popilliae)
This naturally occurring bacterium kills Japanese beetle grubs when ingested. It does not harm beneficial insects. Establishing milky spore in the soil provides long-term grub control.
Diatomaceous Earth
The razor-sharp edges of diatomaceous earth damage the waxy outer layer of grubs upon contact. The abrasion leads to dehydration.
Neem Oil
Extracted from the seeds of the neem tree, neem oil can kill grubs as well as repel adult beetles. Look for 100% cold-pressed neem oil.
Insecticidal Soap
Soap-based products disrupt cell membranes of soft-bodied insects like grubs upon contact. However, effects are short lived.
Beneficial Nematodes
Microscopic worms applied to soil seek out and infect grubs with lethal bacteria. Effective but can be pricey.
BT (Bacillus thuringiensis)
This bacteria produces toxins that damage the gut lining of grubs, leading to death. Must be ingested to work.
Always follow label directions when using organic grub killers. Combining two or more methods often boosts control. Maintaining healthy soil and plants is also key for repelling pests naturally.
Chemical vs. Organic Grub Control
Both chemical pesticides and organic options can be effective for controlling grubs, with some key differences:
| Chemical | Organic | |
|---|---|---|
| Speed of Action | Fast knockdown of grubs | May take longer to kill grubs |
| Persistence | Long residual activity (weeks-months) | Shorter residual, Some very short |
| Toxicity | Higher risk of toxicity to bees, pets, people | Lower toxicity risks overall |
| Effects on Soil | May negatively impact beneficial soil microbes | Less harmful to natural soil biology |
| Cost | Chemical treatments are cheaper | Most organic options are more expensive |
| Regulations | Subject to EPA label regulations | Fewer restrictions on most organic products |
An integrated approach using both chemical and organic controls as part of a whole property management plan is often the best long-term grub solution.
Grub Identification Guide
Identifying the type of grub pest can help select the best control methods. Common grub species include:
Japanese Beetle Grub
– Up to 1.5 inches long
– White body, brown head, V-shaped stripes on rear
– Adults are metallic green and copper colored
June Beetle Grub
– Over 2 inches long when mature
– Yellowish white body, dark brown head
– Adults are brown, fly at night
European Chafer Grub
– Up to 1 inch long
– Creamy white body, light brown head
– Adults are light brown beetles
Asiatic Garden Beetle Grub
– Up to .75 inch long
– White body, brown head
– Adults are brown beetles active at night
Oriental Beetle Grub
– Up to 1.25 inches long
– White C-shaped grub, mottled pattern
– Shiny black adult beetles feed on flowers
Identifying the type of grub pest can help select the best organic or chemical control methods tailored to that species. Proper identification also ensures using the safest, most effective products for the grub species in your lawn or garden.
Conclusion
Grub worms can certainly wreck havoc on lawns and gardens if left uncontrolled. However, there are now many effective options available to kill grubs at all stages in their life cycle. An integrated pest management approach combining natural predators, organic treatments, preventative cultural practices, and targeted chemical control when needed provides the best protection against grubs long-term.
Educating yourself about grub life cycles, monitoring regularly, and knowing your control options are key to protecting your yard from beetle infestations. A persistence multi-pronged approach brings successful results. With proper prevention and control methods, you can defend your lawn and landscape plants against those hungry little grub worms.