Beneficial Nematodes SF – Targets Fungus Gnats, Thrips, Shore Flies & More

What Sf Nematodes Target

• Borers: lesser cornstalk borer, raspberry crown borer, mint root borer (in combination with Hb)
• Larvae & Maggots: fungus gnats (Sciarid), thrips pupae, cabbage maggot, gall midge, humpbacked (phorid) flies, leafminers, onion maggot, root maggot, shore flies
• Others: root aphids, ticks (in combination with Hb)

Steinernema feltiae · How to Say It: sty-ner-NEE-muh FEL-tee-eye, or just "Sf"

Biological soil pest control for outdoor and indoor growing spaces.

Introduction to Sf Beneficial Nematodes

Have you ever sprayed for fungus gnats or thrips only to still see them bouncing back after every treatment? Fungus gnat larvae and thrips pupae stay tucked into the top layer of soil or growing medium, right where most pest control efforts miss them. These soil-dwelling pests spend a critical part of their life cycle just below the surface, out of reach of anything that doesn't penetrate the soil.

Steinernema feltiae (Sf) operates as a "shallow cruiser," staying active in the upper few inches of soil or growing medium. As a biological soil treatment, it targets pest populations in the shallow band of soil where fungus gnat larvae and thrips pupae develop. This application goes straight to the source, giving you targeted, natural pest control for the specific pest stages that live where they're hardest to reach. It's a standard pick for indoor and greenhouse growing environments.

What Beneficial Nematodes Are

Nematodes are microscopic, unsegmented roundworms found in nearly any growing environment. Under a microscope, they appear translucent and slightly tapered, curling into an S or J shape at rest. There's no way to spot one with the naked eye.

Beneficial nematodes are entomopathogenic, meaning they infect insects. They are different from plant-parasitic nematodes, which feed on plant roots and cause real harm. Rather than feeding on plant tissue, beneficial nematodes hunt down soil pests directly, infect them, and let their symbiotic bacteria do the rest. That distinction is what separates a beneficial nematode from a harmful one, and it's the whole reason this is a soil treatment rather than a soil problem.

How Beneficial Nematodes Work

The life cycle follows the same pattern as other beneficial nematodes: eggs hatch into non-feeding juveniles, which molt into infective juveniles that search the shallow soil layer for hosts, infect them with bacteria, and feed on the cadaver before repeating the cycle. What sets Sf apart is temperature tolerance: it's the most cold-tolerant of the three species we carry.

When to Use Sf Nematodes

Beneficial nematodes work best applied preventively at the first sign of pests, like fungus gnats hovering around soil or pots, or thrips pupae showing up in your pest monitoring. The earlier you treat the upper soil layer, the fewer larvae and pupae get the chance to mature into breeding adults.

Because fungus gnat (Sciarid) populations reproduce continuously in moist growing media, plan on reapplying Sf every 3 to 4 weeks rather than expecting a single treatment to fully break the cycle.

Pairing for Broad-Spectrum Soil-Pest Control

Using beneficial nematodes with other predators closes the gap between immobile and mobile soil-dwelling pests, and those that have moved above ground.

• Heterorhabditis bacteriophora (Hb) nematodes: works deeper in the soil profile, targeting grubs and beetle larvae.
• Steinernema carpocapsae (Sc) nematodes: works at the soil surface, in mulch and leaf litter, targeting fleas and small caterpillars.
• Triple Blend Mix: contains all three nematode species, Sf+Sc+Hb.
• Hypoaspis miles (Stratiolaelaps scimitus): a soil-dwelling predator in the top layer of soil that feeds on fungus gnat larvae directly. Combining the two adds a second predator alongside Sf's activity for fuller fungus gnat coverage.
• Orius insidiosus (Minute Pirate Bug) and Amblyseius cucumeris: target thrips once they've emerged from the soil onto foliage, while Sf handles the pupal stage in the soil below. Together, this covers thrips at both the soil and plant level. The Thrips Control Garden Pack bundles the Minute Pirate Bug, A. cucumeris, and Sf nematodes.
• Sticky Traps: the Thrips Trap Kit for adult thrips, or the Gnat Stix Traps / Arber Sticky Traps for adult fungus gnats.

Safe, Sustainable Pest Management

• Natural biological control with no synthetic pesticides
• Safe around people and pets when used as directed
• Safe for use on edible crops when used as directed, with no waiting period before harvest
• Fits seamlessly into existing IPM programs
• Requires no protective equipment

Application Rates

These are general starting points. Actual application should be adjusted based on pest species, plant type, and infestation severity. Monitor pest and predator populations regularly to gauge how well the program is working.

Soil Temperature Range

• Sf works best in soil about 57–79°F. It stays active down to about 46°F; below that it slows down but isn't harmed. Upper limit about 88°F.
• Beneficial nematodes need consistently moist soil. Avoid drying out.
• Keep soil moist for two weeks following application. Avoid runoff when watering.

How to Apply Sf Nematodes

Apply indoors any time. Outdoors, stick to early morning, late evening, or a cloudy day; direct sunlight and UV rays kill nematodes. Wet the soil before and after application, and keep the ground damp for at least two weeks so the nematodes can move.

1. Prepare the Soil: Water the treatment area first. Nematodes move through water, so dry soil stops them from reaching the fungus gnat larvae and thrips pupae in the upper soil layer.
2. Mix the Solution: Combine the Sf nematodes with water between 59°F and 69°F. Water volume depends on treatment area size and infestation severity. Use the mixed solution within 1–2 hours; it stays viable up to 6 hours, but weakens the longer it sits.
3. Apply to the Soil: Distribute the mixed solution evenly using a watering can, pump sprayer, hose-end sprayer, or irrigation system, whichever you already have on hand. Full, even coverage isn't necessary, since nematodes move through the soil on their own from there.
4. Keep the Area Moist: Water lightly right after application, then maintain consistent soil moisture for two weeks. Avoid heavy watering that causes runoff, since that can wash nematodes out of the treatment zone.

Watering Can or Pump Sprayer

• Moisten the soil beforehand to avoid runoff and improve habitat.
• Mix 5 million nematodes with 1–5 gallons of water (59–69°F) to cover the desired area, diluting as needed for coverage.
• Water the treated area immediately after application and keep soil moist for two weeks.

Hose-End Sprayer

Use room-temperature water and let the nematode powder sit for 15 minutes to fully dissolve before spraying. Remove any screen filter first. Keep pressure at or below 72 PSI and use a nozzle 0.8 mm or larger.

Other Hose-End Sprayers (dial-style)

Use room-temperature water and let the nematode powder sit for 15 minutes to fully dissolve before spraying. Remove any screen filter first.

Pro Tips

• If you're dealing with fleas or surface-active pests, Sc is a better fit; for deeper-dwelling grubs, Hb is the one to use. If you're not sure, the Triple Blend Mix will cover all the bases.
• Avoid flushing nematodes away by minimizing runoff when watering.
• Check for water retention and drainage in the areas to be treated to ensure watering is effectively penetrating the soil.

Chemical Compatibility

Some chemicals, including pesticides and fertilizers, can harm or even eliminate beneficial nematodes, reducing their effectiveness as natural pest controllers. To protect your nematodes, it's essential to check chemical compatibility before applying it to your soil.

To make it easier, we've created a detailed list of chemicals that work safely with beneficial nematodes, ensuring your garden stays healthy.

Before Activation

Your nematodes arrive in a bubble mailer with an ice pack. If your order includes other items or totals over $200, it ships in a free cooler in a 12×12×12 box. It's normal for the ice pack to have melted and feel warm on arrival; the product remains effective to use. If you're not applying right away, refrigerate the unopened package at 36–45°F in a dark place for no more than 30 days. Do not freeze.

After Activation

Apply the mixed solution within 1–2 hours. Nematodes stay viable up to 6 hours after mixing, but they sink and start to drown, so they weaken the longer they sit.

Where do Sf nematodes live day to day?
Anywhere the soil stays consistently damp. Garden beds, potted soil, greenhouse benches, and container mixes are all viable habitat for Sf specifically.

Can I use Sf nematodes alongside neem oil or insecticidal soap?
Yes, but timing matters. Apply nematodes a few days apart from any foliar spray, since some residue can affect nematode survival in the soil. Nematodes themselves pose no risk to your other treatments.

How often do I need to apply Sf nematodes?
Since fungus gnat populations reproduce continuously in moist soil, monthly reapplication is recommended for ongoing control rather than a single treatment.

Are Sf nematodes safe to use around edible plants?
Yes. Sf nematodes are safe for use on edible crops with no waiting period before harvest, and they're safe around people and pets when used as directed.

Are beneficial nematodes eco-friendly, and safe around pets, kids, and pollinators?
Yes. Sf nematodes are a natural biological soil treatment with no synthetic chemicals involved. They're safe around people, pets, and kids when applied as directed, and because they work below the soil surface on soil-dwelling pest stages, they don't come into contact with pollinators the way a foliar spray would.

Will Sf nematodes harm earthworms or other beneficial soil organisms?
Sf nematodes target insect pests like fungus gnat larvae and thrips pupae and aren't known to harm earthworms, beneficial soil microbes, or other non-target organisms in your soil.

How long do beneficial nematodes live in the soil once applied?
As long as pest levels stay high enough to sustain reproduction, the population can persist in the ground; once hosts become scarce, numbers decline fairly quickly. That natural decline is the main reason reapplication every 3 to 4 weeks keeps control consistent rather than relying on one release to last all season.

How long until I see results?
Beneficial nematodes start working once they're in moist soil.

I've heard nematodes can damage plants. How do I get rid of nematodes if that's my problem instead?
That's a different category of nematode. Plant-parasitic species (like root-knot nematodes) feed on roots and can genuinely harm a garden, but they're biologically unrelated to the beneficial, insect-targeting nematodes. Beneficial nematodes don't feed on plant tissue at all. If you're dealing with root damage and suspect plant-parasitic nematodes, that's typically managed through crop rotation, resistant plant varieties, or a soil test to confirm what's actually present.

Where can I buy beneficial nematodes?
Right here at NaturesGoodGuys. Beneficial nematodes ship fresh to your door.

How do I know if a single species or combination is best?
Use these charts to narrow your search:

Beetle Larvae (Grubs)

Moth Larvae (Caterpillars)

Borers (Tunneling Larvae)

Weevil Larvae (Grubs)

Fly Larvae & Maggots

Miscellaneous Larval Pests

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We do not provide recommendations on pesticide use. Products are sold for home use only, not commercial use.

QUALITY GUARANTEE

If your beneficial insects or other perishable products are not viable when delivered, email info@naturesgoodguys.com within 48 hours of delivery with your order number and a description of the problem. Photos may be requested. Approved replacements ship on Wednesdays and Thursdays.

• Open your package right away and check for storage instructions. Some products need refrigeration, and improper storage voids the guarantee.
• Ice packs help moderate temperature in transit and are not expected to arrive frozen.
• Some insects need time at room temperature before they become active, and many are hard to see without magnification.

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RETURNS AND REPLACEMENTS

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Replacements are not available for an incorrect shipping address, storage or use instructions not followed, or packages left uncollected after delivery.