What Is Methomyl?

Methomyl is a fast-acting, broad-spectrum insecticide widely used in agriculture and commercial pest control. Known for its high efficacy against a variety of chewing and sucking insects, methomyl plays a key role in protecting crops from severe infestations. This guide provides a complete overview of methomyl—what it is, how it works, where it’s used, and what you should know about safety, regulations, and environmental impact.

What Is Methomyl?

Methomyl is a carbamate insecticide with systemic and contact activity. It was introduced in the 1960s and is primarily used for the control of insect pests in field crops, vegetables, fruits, and ornamental plants. It is classified under Group 1A (carbamates) in the IRAC (Insecticide Resistance Action Committee) mode of action classification.

• Chemical Name: S-methyl N-[(methylcarbamoyl)oxy]thioacetimidate

• CAS Number: 16752-77-5

• Mode of Action: Acetylcholinesterase inhibitor

• Formulations: Soluble powder (SP), emulsifiable concentrate (EC), water-dispersible granules (WDG), bait formulations

How Methomyl Works

Methomyl acts by inhibiting acetylcholinesterase (AChE), an essential enzyme in the nervous system of insects. When this enzyme is blocked, nerve impulses cannot be stopped, leading to overexcitation, paralysis, and death.

Methomyl works in multiple ways:

• Contact Activity: Kills insects that come into direct contact with the spray

• Ingestion Activity: Highly toxic to insects that feed on treated plant tissue

• Systemic or translaminar movement: Limited systemic action, but penetrates leaf surfaces effectively

It is particularly effective for quick knockdown of pests, making it useful during outbreaks.

What Pests Does Methomyl Control?

Methomyl is effective against a wide range of chewing and sucking insects, including but not limited to:

• Lepidoptera (e.g., armyworms, bollworms, leafrollers)

• Diptera (e.g., flies, leafminers)

• Coleoptera (e.g., beetles, weevils)

• Hemiptera (e.g., aphids, whiteflies, plant bugs)

• Thrips and mites in some formulations

Because of its broad activity, it is often used in integrated pest management (IPM) programs for high-value crops.

Crops Commonly Treated with Methomyl

Methomyl is registered for use on many crop types worldwide:

Application Guidelines

Proper application ensures maximum effectiveness and minimizes resistance risk.

• Timing: Apply at early pest stages (larvae/nymph) for best results

• Method: Foliar spray or bait application, depending on pest type

• Rate: Varies by crop and formulation (typically 100–400 g a.i./ha)

• Interval: 7–14 days between applications; do not exceed maximum annual use

• Compatibility: Compatible with many other insecticides and fungicides (jar test recommended)

Avoid application during high temperatures or when pollinators are active.

Resistance Management

Methomyl belongs to IRAC Group 1A, and resistance has been reported in some insect populations due to overuse.

To manage resistance:

• Rotate with insecticides from different IRAC groups

• Use methomyl only when necessary, based on pest scouting

• Incorporate non-chemical control measures (crop rotation, natural enemies)

Safety and Toxicology

Methomyl is classified as highly toxic to humans and animals if not handled properly.

Human and Mammalian Toxicity

• LD50 (oral, rats): 17–24 mg/kg (highly toxic)

• May cause headache, nausea, muscle twitching, respiratory issues

• Personal Protective Equipment (PPE) is required when handling

Environmental Toxicity

• Highly toxic to bees: Avoid spraying during flowering or bee activity

• Toxic to fish and aquatic invertebrates

• Avoid runoff to waterways and apply buffer zones when needed

Always follow national guidelines and product safety data sheets (MSDS).

Regulatory Status

Methomyl is:

• Restricted use in many countries due to its toxicity profile

• Subject to maximum residue limits (MRLs) in food crops

• Approved under emergency use authorizations in some markets

Its use is regulated in regions such as the U.S., EU, China, Brazil, and Australia. Importers and distributors must ensure compliance with local pesticide registration laws.

Alternatives and Combination Options

To improve efficacy or reduce methomyl use, it is often:

• Mixed with pyrethroids or neonicotinoids for broader spectrum and dual mode of action

• Rotated with products like emamectin benzoate, chlorantraniliprole, indoxacarb, or spinosad to reduce resistance pressure

Conclusion: Should You Use Methomyl?

Methomyl remains a valuable tool in pest management where rapid knockdown is required. If you are managing high-value crops or resistant pest outbreaks, this active ingredient offers:

• Fast action and broad-spectrum control

• Flexibility across many crop types

• Effectiveness against resistant or hard-to-kill pests

However, due to its high toxicity, careful handling, responsible use, and proper rotation are critical. When used correctly, methomyl is a highly effective option within a well-balanced crop protection program.