Does Merit Kill Earthworms? The Hidden Impact

Merit is a widely used insecticide that contains the active ingredient imidacloprid. This systemic pesticide is applied to lawns, turf, and agricultural land to control grubs, lawn pests, and other insects. But what about our wiggly garden helpers, the earthworms? Does Merit kill earthworms too?

Unfortunately, the answer is yes, Merit insecticide is highly toxic to earthworms. Even small amounts of imidacloprid residue in soil can be lethal to earthworm populations over time.

Keep reading to understand how Merit impacts earthworms and what you can do to protect these beneficial organisms.

The information ahead will show you how important earthworms are and ways we can keep them thriving in our yards and gardens!

Does Merit Kill Earthworms
Does Merit Kill Earthworms

What is Merit and How Does it Work?

Merit, the brand name for the chemical compound imidacloprid, is a systemic insecticide belonging to the neonicotinoid class. It is widely used to control pests such as grubs, beetles, and aphids in lawns, gardens, and agricultural settings. Merit works by interfering with the nervous system of insects, leading to paralysis and eventual death.

How Merit insecticide affects earthworms?

To understand why Merit is so deadly for earthworms, we need to look at how it works:

It binds to soil particles

Imidacloprid has a high soil binding affinity, meaning it sticks tightly to soil particles after application.

It persists for months

The half life of imidacloprid in soil is around 40-300 days, allowing it to persist for weeks or months.

It dissolves in water

Merit dissolves in water, spreading dissolved imidacloprid throughout the soil layers. Earthworms take in the insecticide as they ingest soil particles.

It is systemically toxic

Imidacloprid works systemically, meaning once absorbed it spreads throughout the earthworm’s tissues, organs, and nervous system.

It attacks nerve transmission

The chemical disrupts nerve impulses, leading to paralysis and death in earthworms within hours to days of exposure.

Given these characteristics, even a single application of Merit at recommended rates can provide long-lasting contamination of soil with imidacloprid and cause toxicity or death to earthworms over time.

How toxic is Merit to earthworms?

Research studies have quantified just how poisonous small amounts of imidacloprid residue can be for earthworms:

  • 0.45 mg/kg soil – Caused 100% mortality in one species of earthworm in under 48 hours.
  • 1-3 mg/kg soil – Decreased survival, growth rate, and reproduction in multiple earthworm species.
  • 5 mg/kg soil – Resulted in zero survival of earthworms after just 20 days of exposure.

To put this into perspective, the recommended application rate for Merit insecticide on lawns and turf is around 1.4 mg/kg soil. While some earthworms may initially survive, the long-lasting residues will accumulate and kill earthworms over time.

In addition to direct mortality, sub-lethal doses of imidacloprid negatively affect earthworm behavior, immune function, enzymatic activity, and cellular health. There is no safe level of Merit exposure for earthworms.

Effects of Merit on earthworm populations

Unfortunately, the impacts of imidacloprid on earthworms have been clearly demonstrated through scientific studies:

  • Lower abundance – Soils treated with Merit have significantly fewer earthworms compared to untreated soils. Declines by over 60% have been observed.
  • Reduced biomass – In addition to lower numbers, the total weight and density of earthworms in contaminated soils is drastically decreased.
  • Fewer species – Imidacloprid application reduces earthworm diversity as sensitive species disappear. One study found a loss of 3-4 species after treatment.
  • Altered composition – As sensitive earthworm types are eliminated, the relative composition shifts towards more tolerant species
  • Slow recovery – Even years after initial exposure, earthworm populations often fail to fully rebound as imidacloprid break down takes months.

By decimating earthworm populations, the ecological benefits they provide are lost. Protecting existing earthworm communities from Merit should be a priority.

Safer alternatives to Merit for lawns

If you want to keep earthworms thriving, the only sure way is to avoid using Merit and other products containing imidacloprid altogether. Some safer options include:

Beneficial nematodes

Helpful nematodes kill grubs without harming earthworms when applied early in the season. Brands like ScanMask and GrubEx are effective and non-toxic.

Milky spore powder

This natural bacterium only infects and kills Japanese beetle grubs while being safe for earthworms. Apply in early summer.

Diatomaceous earth

The powdered mineral physically dries out insects but does not harm worms. Dust it onto lawns.

Top dressing with compost

Enriches lawn soil, boosts beneficial microbes, and repels pests while being worm-friendly.

Adjusting watering and mowing practices

Smart watering, fertilization, aeration, overseeding, and mowing height strengthens turfgrass to better resist pests without poison.

With a little proactive organic lawn care, you can keep earthworms thriving and avoid the need for toxic insecticides like Merit that will decimate helpful earthworms.

What to do if Merit was already applied?

If you or your lawn care provider unfortunately already used Merit, don’t lose hope! Here are some steps to help protect and replenish any surviving earthworms:

  • Water the lawn thoroughly to dilute residues and reduce toxicity to earthworms.
  • Apply beneficial microbes to help metabolize imidacloprid faster. Products with Pseudomonas species can accelerate breakdown.
  • Top dress the lawn with 1/2 inch of vermicompost or compost to provide an uncontaminated refuge and food source for earthworms.
  • Overseed with clover to re-introduce deep rooting earthworm attractors.
  • Adjust to organic lawn care practices to avoid any further pesticide use.
  • Be patient and avoid additional applications of Merit or other insecticides to allow earthworms to gradually recover over time.

While there is no way to undo the harm to earthworms, you can take steps to help rebuild populations and restore the soil food web.

Related Guide – Does GrubEx Kill Earthworms?

Key takeaways

  • Merit insecticide contains imidacloprid which is highly toxic and lethal to beneficial earthworms, even at low concentrations.
  • Imidacloprid persists in soil for months, continuously exposing earthworms through contact and ingestion.
  • Earthworms provide invaluable ecological services like soil enrichment, pest control, decomposition, and wildlife food sources. Their loss is detrimental.
  • Alternative organic approaches like beneficial microbes, nematodes, and compost protect lawns without harming earthworms.
  • Avoid applying Merit and other imidacloprid products if you want to sustain healthy earthworm populations in your lawn or garden.

The bottom line is that applying Merit insecticide is incompatible with maintaining vibrant earthworm abundance and biodiversity in your yard. Organic, non-chemical pest management is the worm-friendly way to cultivate a healthy lawn.

Read more – Does Sluggo Kill Earthworms?

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