Contact vs Systemic Herbicides: Differences, Examples, and Selection

Contact and systemic herbicides differ mainly in how they move within a plant.

Contact herbicides primarily damage the plant tissue directly covered by the spray. They usually produce faster visible symptoms, but untreated leaves, growing points, roots, rhizomes, or tubers may remain alive.

Systemic herbicides are absorbed through leaves, roots, or other plant tissues and move beyond the original point of contact. Depending on the active ingredient, they may reach growing points and underground structures, making them generally more suitable for established perennial weeds.

Neither type is automatically better.

The correct choice depends on:

• Weed species
• Annual or perennial growth cycle
• Root and rhizome structure
• Weed size
• Required control speed
• Crop or application site
• Spray coverage
• Environmental conditions
• Resistance status
• Local product registration

Visible speed should not be confused with complete control. A contact herbicide may burn foliage quickly while a perennial weed later regrows from its roots. A systemic herbicide may take longer to show symptoms but provide more complete control after sufficient absorption and translocation.

Contact vs Systemic Herbicides at a Glance

This comparison describes general behavior. The registered label and technical characteristics of the exact active ingredient and formulation remain the controlling references.

What Do Contact and Systemic Actually Mean?

Contact and systemic describe herbicide absorption and movement within plants.

They do not, by themselves, describe the herbicide’s biochemical mode of action.

A mode of action explains the biological process disrupted by an active ingredient. Examples include:

• Photosystem I electron diversion
• Photosystem II inhibition
• EPSPS inhibition
• Glutamine synthetase inhibition
• PPO inhibition
• Synthetic auxin activity
• ACCase inhibition
• ALS inhibition

Two contact herbicides can have different biochemical targets. Two systemic herbicides can also have completely different modes of action.

For example:

• Paraquat is a contact-type Group 22 herbicide that diverts electrons associated with photosystem I.
• Bromoxynil is a contact-type Group 6 photosystem II inhibitor.
• Glyphosate is a systemic Group 9 EPSPS inhibitor.
• 2,4-D is a systemic Group 4 synthetic auxin herbicide.

Contact versus systemic is also different from other herbicide classification systems.

These classification axes can overlap.

A herbicide can be:

• Contact and non-selective
• Contact and selective
• Systemic and non-selective
• Systemic and selective
• Post-emergence and residual
• Pre-emergence and systemic after root uptake

For a separate explanation of plant selectivity, see selective and non-selective herbicides.

How Do Contact Herbicides Work?

Contact herbicides mainly damage the leaves and stems that receive an effective spray deposit.

Once the active ingredient reaches susceptible tissue, it may disrupt:

• Cell membranes
• Photosynthetic electron transport
• Chlorophyll function
• Amino-acid metabolism
• Cellular energy balance
• Other essential plant processes

The specific biochemical effect depends on the active ingredient. “Contact” does not mean every product kills tissue through the same mechanism.

Why Is Movement Limited?

Many contact-type herbicides cause rapid cellular injury near the point of application.

As treated cells lose membrane integrity and normal metabolic function, movement of the herbicide into other plant parts may remain limited.

The result is localized tissue destruction.

If a leaf receives complete coverage, most of that leaf may die. If only part of the leaf receives an effective deposit, untreated sections may remain green.

Underground tissues are especially difficult to control when the active ingredient cannot move from the leaves into roots, rhizomes, stolons, tubers, or bulbs.

Why Does Spray Coverage Matter?

Contact herbicides depend heavily on spray distribution.

The product can only act effectively where sufficient active ingredient reaches susceptible tissue. Poor coverage can leave living sections that continue growing.

Important coverage factors include:

• Weed size
• Leaf angle
• Canopy density
• Spray volume
• Droplet size
• Nozzle selection
• Travel speed
• Spray pressure
• Water quality
• Adjuvant requirements
• Weather
• Leaf-surface characteristics

Large droplets may provide good drift control but insufficient surface distribution for certain contact products. Very small droplets may improve coverage but increase off-target movement.

The correct balance depends on the product label, application equipment, crop, weed canopy, and local regulations.

Why Do Symptoms Usually Appear Faster?

Contact herbicides often damage essential cellular structures rapidly.

Depending on the active ingredient, visible effects may include:

• Water-soaked lesions
• Leaf spotting
• Wilting
• Loss of green color
• Tissue bronzing
• Rapid desiccation
• Brown or black necrosis

Fast symptoms do not necessarily mean the entire weed is dead.

A perennial weed may lose its treated foliage but still retain enough stored energy in underground tissues to produce new shoots.

How Do Systemic Herbicides Move Through Plants?

Systemic herbicides are absorbed into plant tissue and transported beyond the original point of application.

Movement depends on:

• Where the herbicide enters
• Its chemical properties
• Plant vascular flow
• Weed growth stage
• Source-to-sink relationships
• Environmental conditions
• Formulation
• Plant susceptibility

Some systemic herbicides are absorbed mainly through foliage. Others enter mainly through roots. Some can enter through both routes.

Foliar Absorption and Phloem Movement

Foliar-applied systemic herbicides must first pass through the leaf surface.

After absorption, certain active ingredients move through the phloem with sugars and other plant metabolites.

Phloem movement can carry the herbicide toward active sinks such as:

• New shoots
• Growing points
• Developing leaves
• Roots
• Rhizomes
• Tubers
• Reproductive structures

Glyphosate is a common example of a foliar-applied systemic herbicide that can move toward actively growing tissues and underground storage structures.

This movement is one reason glyphosate is often considered for deep-rooted or rhizomatous perennial weeds where locally registered.

However, translocation requires time. Rapid mowing, cultivation, or tissue destruction shortly after treatment may reduce movement to underground structures.

Root Absorption and Xylem Movement

Some systemic herbicides enter through plant roots.

Once absorbed, they may move upward through the xylem with the transpiration stream.

Xylem-mobile herbicides generally move toward:

• Stems
• Expanding leaves
• Older transpiring leaves
• Other above-ground tissues

This direction of movement differs from the source-to-sink phloem transport associated with some foliar-applied products.

Therefore, the word “systemic” does not guarantee that an active ingredient will move equally:

• Upward
• Downward
• Into every root
• Into every rhizome
• Into every growing point

The absorption route and vascular pathway must be understood for the specific herbicide.

Why Do Systemic Herbicides Usually Act More Slowly?

A systemic herbicide must complete several stages:

1. Deposit on or near the plant
2. Penetrate the leaf or root
3. Enter internal tissues
4. Move through the vascular system
5. Reach susceptible growing regions
6. Disrupt the biochemical target
7. Produce enough injury to stop plant growth
8. Deplete the plant’s ability to recover

Visible symptoms may therefore take longer than with contact products.

Depending on the mode of action, symptoms may include:

• Growth cessation
• Gradual yellowing
• Red or purple discoloration
• Stem twisting
• Leaf cupping
• Growing-point death
• Progressive wilting
• Slow whole-plant decline

A lack of immediate leaf burn does not prove that the treatment has failed.

Do Contact Herbicides Kill Roots?

Contact herbicides generally provide limited root control because they do not move efficiently from treated leaves into underground structures.

They may still kill a small annual weed when:

• The entire shoot receives adequate coverage
• The weed has a limited root system
• The growing point is exposed
• The plant has little stored energy
• Treatment occurs at an early growth stage

Established perennial weeds are more difficult.

They may survive through:

• Taproots
• Rhizomes
• Stolons
• Tubers
• Bulbs
• Underground buds
• Root fragments

After the treated foliage dies, these structures may produce new growth.

This response is sometimes described as chemical mowing: the above-ground vegetation is removed, but the plant is not completely eliminated.

Systemic herbicides generally offer a better opportunity to reach underground structures, but root control is still not guaranteed. The product must be:

• Active against the weed species
• Absorbed in sufficient quantity
• Applied at the correct growth stage
• Allowed enough time for translocation
• Used under suitable environmental conditions
• Applied according to the registered rate and label

Resistance, drought stress, mature foliage, dust, poor coverage, rain, and incorrect timing can all reduce systemic control.

Which Is Better for Annual and Perennial Weeds?

Weed biology is more important than visible symptom speed.

Young Annual Weeds

Annual weeds complete their life cycle within one growing season and rely primarily on seed production.

Small annual weeds often have:

• Limited leaf area
• Small root systems
• Exposed growing points
• Low underground energy reserves
• Less capacity to regrow after complete shoot destruction

Contact herbicides can therefore provide strong control when young annual weeds receive uniform coverage.

Systemic herbicides can also control annual weeds. The decision depends on the crop, weed spectrum, resistance status, required speed, and registered program.

Established Annual Weeds

Large or mature annual weeds can be more difficult for both types.

Potential problems include:

• Dense foliage that prevents full coverage
• Hardened or waxy leaf surfaces
• Large biomass
• Protected growing points
• Reduced active growth
• Flowering or seed production
• Herbicide resistance

A contact product may burn the outer canopy while leaving internal tissue alive. A systemic product may be absorbed too slowly or incompletely if the plant is stressed or mature.

Early treatment normally provides a more reliable result than attempting to rescue a program after weeds become large.

Perennial Weeds

Perennial weeds survive for more than one growing season and may reproduce through seed and vegetative structures.

Examples of underground survival systems include:

• Deep taproots
• Rhizomes
• Tubers
• Stolons
• Creeping roots
• Bulbs
• Root crowns

Systemic herbicides are generally more suitable when the objective is to move active ingredient into these underground structures.

Timing remains critical.

For many perennial weeds, stronger downward translocation occurs when the plant is moving carbohydrates toward roots or storage organs. The most appropriate timing varies by species, growth stage, climate, crop, and product label.

Woody and Invasive Vegetation

Woody vegetation may require a systemic product capable of moving through vascular tissue.

However, control depends on:

• Species
• Stem diameter
• Treatment method
• Seasonal growth
• Bark characteristics
• Product formulation
• Registered application site

A contact herbicide may remove exposed foliage without controlling the root crown or woody tissues.

Examples of Contact and Systemic Herbicides

The following table provides general examples. Product classification, selectivity, approved uses, and application conditions must be verified from the local label.

Paraquat

Paraquat is a Group 22 contact herbicide.

It accepts electrons associated with photosystem I and transfers them to oxygen, producing reactive oxygen species. These molecules damage membrane lipids and cause rapid cell leakage and tissue desiccation.

Paraquat does not primarily work by preventing chlorophyll formation.

Its rapid activity means thorough spray coverage is important. It can provide strong burndown of small annual weeds but normally has limited movement to underground perennial structures.

For a more detailed mechanism explanation, see how paraquat affects photosynthesis.

Diquat

Diquat is also a Group 22 contact herbicide with limited movement within plants.

It produces rapid oxidative damage and cell-membrane disruption after exposure to light.

Diquat is not a bioherbicide. It is a synthetic herbicide used in registered agricultural, industrial, desiccation, and aquatic applications, depending on the market and product label.

Because its activity is concentrated in treated tissue, uniform coverage is important.

Glufosinate

Glufosinate inhibits glutamine synthetase and causes ammonium accumulation, photosynthetic disruption, and tissue injury.

It is often described as contact-like or contact-dominant because movement within plants is limited compared with glyphosate.

Glufosinate generally performs best on small, actively growing weeds with good coverage. Large weeds, dense canopies, and poor application conditions can reduce control.

Glyphosate

Glyphosate is a systemic Group 9 herbicide that inhibits EPSPS, an enzyme involved in aromatic amino-acid synthesis.

After foliar absorption, it can move through the phloem toward active growing points and underground structures.

This makes it suitable for many annual and perennial weeds where registered and where the population remains susceptible.

Performance is normally stronger when weeds are healthy and actively growing. Severe drought, extreme temperatures, dust, mature foliage, poor water quality, or insufficient absorption time may reduce control.

2,4-D

2,4-D is a systemic Group 4 synthetic auxin herbicide.

It moves within susceptible plants and causes abnormal growth, tissue disruption, stem twisting, and growing-point failure.

It is commonly used to control susceptible broadleaf weeds in tolerant cereal crops, corn, pastures, turf, and non-crop areas where registered.

It should not be described as harmless to all grasses. Crop species, formulation, rate, timing, temperature, and label conditions determine selectivity.

Clethodim

Clethodim is a systemic Group 1 ACCase inhibitor used to control susceptible annual and perennial grasses in labeled broadleaf crops.

After foliar absorption, it moves toward grass growing points and underground structures.

Visible symptoms may take time to develop. The youngest leaves may become discolored or pull easily from the growing point as injury progresses.

Which Type Produces Faster Results?

Contact herbicides usually produce faster visible symptoms.

However, the actual speed depends on:

• Active ingredient
• Mode of action
• Weed size
• Spray coverage
• Light
• Temperature
• Humidity
• Plant growth
• Formulation
• Application rate

Systemic herbicides usually take longer because absorption and translocation must occur before the entire plant is affected.

The better question is not:

Which herbicide looks faster?

It is:

Which herbicide provides the required level and duration of control for the target weed?

Fast tissue burn can sometimes hide incomplete control. Post-treatment monitoring is necessary before deciding whether the program succeeded.

How Do Application Conditions Affect Contact Herbicides?

Contact herbicides depend heavily on successful spray deposition.

Weed Size

Small weeds are generally easier to cover.

As weeds grow:

• Leaf area increases
• Canopies become denser
• Growing points become protected
• Lower leaves receive less spray
• Biomass requires more complete coverage

Late application can therefore reduce consistency.

Droplet Distribution

Contact products often require sufficient droplets across the leaf surface.

An application that deposits only a few large droplets may leave substantial untreated tissue between impact points.

Nozzle and droplet decisions must still balance coverage against drift control and label requirements.

Light and Temperature

Light strongly influences the activity of certain contact herbicides, particularly Group 22 active ingredients.

Warm, sunny conditions may accelerate visible injury for some products, but extreme heat, evaporation, crop sensitivity, and application restrictions must also be considered.

Glufosinate performance is often influenced by temperature, humidity, light, weed size, and coverage. These relationships should be evaluated according to the specific formulation and label.

Rain After Application

Rain can remove herbicide that has not yet been retained or absorbed.

Rainfast periods vary between:

• Active ingredients
• Formulations
• Adjuvant systems
• Weather conditions
• Product labels

A universal rainfast period should not be applied to every contact herbicide.

How Do Application Conditions Affect Systemic Herbicides?

Systemic herbicides require adequate absorption and movement.

Active Plant Growth

Healthy, actively growing plants normally support stronger transport through vascular tissues.

Drought, cold, flooding, nutrient deficiency, disease, or other stress can slow:

• Leaf penetration
• Vascular transport
• Movement to growing points
• Herbicide metabolism
• Symptom development

A stressed weed may remain alive without absorbing or moving enough active ingredient for complete control.

Leaf Area

Foliar systemic products need sufficient green leaf area.

Weeds that have been:

• Recently mowed
• Grazed
• Cut
• Burned
• Damaged by frost
• Injured by a contact herbicide

may not have enough active foliage to absorb an effective dose.

Time Before Disturbance

Mowing, tillage, cutting, or grazing too soon after application may remove treated tissue before sufficient translocation occurs.

The required interval depends on the product label and weed-management program.

Water Quality and Formulation

Hard water, suspended soil, pH, salts, incompatible additives, and spray-tank contamination can affect certain systemic products.

Any conditioner or adjuvant should only be used when permitted and supported by the registered label.

Rainfastness

Systemic herbicides require enough time to enter plant tissue.

Rain shortly after application may reduce uptake. The required rain-free interval varies by active ingredient and formulation.

Contact vs Systemic Is Not the Same as Selective vs Non-Selective

A common misunderstanding is that all contact herbicides are non-selective and all systemic herbicides are selective.

This is incorrect.

Contact and Non-Selective

Examples may include:

• Paraquat
• Diquat
• Glufosinate

These products can injure many green plants they contact, subject to resistance traits and label conditions.

Contact and Selective

Examples may include:

• Bromoxynil
• Lactofen
• Fomesafen

These products can control selected weeds in tolerant crops when used according to the label.

Systemic and Non-Selective

Glyphosate is a common example. It moves within susceptible plants and can control both grasses and broadleaf weeds.

Systemic and Selective

Examples include:

• 2,4-D for susceptible broadleaf weeds
• Clethodim for susceptible grasses
• Metsulfuron-methyl in labeled crops or non-crop sites

Movement and selectivity answer different questions:

• Contact or systemic: Where does the herbicide move?
• Selective or non-selective: Which plants can tolerate the treatment?

Contact vs Systemic Is Not the Same as Pre- vs Post-Emergence

Contact herbicides normally require emerged plant tissue, so they are generally associated with post-emergence application.

Systemic herbicides can be:

• Foliar post-emergence products
• Root-absorbed pre-emergence products
• Root-absorbed early post-emergence products
• Products with both foliar and soil activity

Pre-emergence and post-emergence describe when the product is applied relative to weed emergence.

They do not describe how the herbicide moves after entering a plant.

For a detailed comparison, see pre-emergent vs post-emergent herbicides.

Does Systemic Mean Residual?

No.

A systemic herbicide moves within an exposed plant. A residual herbicide remains biologically available in the soil or another treatment zone for a period after application.

Glyphosate is systemic within plants but normally provides little useful residual weed control after contact with soil.

Atrazine can be absorbed through roots and foliage and can also provide residual soil activity.

Paraquat is contact-active on green tissue and becomes strongly bound to soil, so it is not generally positioned for residual weed control.

These properties should be assessed separately:

• Plant movement
• Soil persistence
• Bioavailability
• Absorption route
• Application timing
• Crop selectivity
• Environmental behavior

Can Contact and Systemic Herbicides Be Mixed?

Some registered herbicide programs allow a contact product and a systemic product to be used together.

Potential objectives include:

• Broader weed spectrum
• Faster visible burndown
• Multiple effective modes of action
• Management of mixed grass and broadleaf populations
• Control of weeds at different growth stages

However, contact and systemic combinations are not automatically beneficial.

A rapidly acting contact partner can sometimes injure leaf tissue before the systemic component has completed absorption and translocation. This may reduce movement toward roots or growing points and produce antagonism.

Other potential problems include:

• Physical incompatibility
• Crop injury
• Reduced absorption
• pH changes
• Precipitation
• Excessive foam
• Nozzle blockage
• Drift risk
• Conflicting label restrictions
• Overlapping environmental limits

Research on some glyphosate and diquat combinations has shown that rapid contact injury can reduce glyphosate translocation and weaken long-term control compared with glyphosate alone.

This does not mean every contact-systemic mixture will fail. It means the mixture must be supported by:

• Both product labels
• Crop registration
• Target-weed biology
• Compatibility information
• Local agronomic evidence
• Resistance-management logic

The more restrictive label requirement must be followed. A general comparison article should not provide a universal tank-mix ratio.

How Should Importers and Distributors Choose?

For professional buyers, contact versus systemic is a portfolio decision rather than a single-product judgment.

The correct product should match the dominant weed problem and customer application system.

Before selecting a formulation, importers and distributors should confirm:

• Destination country
• Registered crops or use sites
• Dominant weed species
• Annual or perennial weed cycle
• Grass or broadleaf spectrum
• Underground reproductive structures
• Weed growth stage
• Resistance status
• Required speed of control
• Application equipment
• Water quality
• Climate and application season
• Active ingredient
• Mode-of-action group
• Formulation
• Packaging
• Label language
• COA, SDS or MSDS, and TDS requirements
• Annual purchasing volume

A market with deep-rooted perennial weeds should not be supplied only with rapid contact products.

A market requiring fast burndown of small annual weeds may not need a slow systemic product for every program.

A balanced herbicide portfolio may include both types, each positioned for a defined use rather than marketed as a universal solution.

Common Product-Positioning Mistakes

Promoting Contact Herbicides as Permanent Root Control

Rapid brown foliage can create a strong visual result, but it does not prove that roots or rhizomes are dead.

This claim is especially risky for:

• Bindweed
• Canada thistle
• Johnsongrass
• Quackgrass
• Nutsedge
• Other vegetatively reproducing weeds

Promoting Systemic Herbicides as Effective on Every Weed

Movement within the plant does not overcome:

• Natural tolerance
• Herbicide resistance
• Incorrect weed identification
• Poor timing
• Inadequate dose
• Environmental stress
• Label limitations

Using “Fast” as the Main Measure of Product Quality

Fast symptoms may support customer confidence, but long-term control should be assessed through regrowth monitoring.

Treating All Formulations as Equivalent

Different salts, esters, concentrations, surfactant systems, and formulation types can affect:

• Absorption
• Coverage
• Rainfastness
• Handling
• Crop safety
• Packaging
• Storage
• Registration

Ignoring Application Equipment

A product that performs well with professional field equipment may deliver inconsistent results through unsuitable nozzles, low spray volume, or poorly calibrated equipment.

Frequently Asked Questions

What is the main difference between contact and systemic herbicides?

Contact herbicides mainly damage the plant tissue directly covered by the spray. Systemic herbicides are absorbed and move beyond the treated tissue.

Which type works faster?

Contact herbicides usually produce faster visible symptoms. Systemic herbicides generally require more time for absorption, translocation, and whole-plant injury.

Do contact herbicides kill roots?

They usually provide limited root control. Small annual weeds may die after complete shoot destruction, but established perennial weeds can regrow from underground structures.

Do systemic herbicides always kill the roots?

No. They may reach roots or rhizomes, but successful control depends on the active ingredient, weed susceptibility, application timing, absorption, movement, and resistance status.

Which is better for annual weeds?

Contact herbicides can work well on small annual weeds with good coverage. Systemic products can also be effective. Weed species, size, crop, and resistance should guide the choice.

Which is better for perennial weeds?

Systemic herbicides are generally more suitable because selected active ingredients can move toward roots, rhizomes, tubers, and growing points.

Is glyphosate a contact or systemic herbicide?

Glyphosate is a systemic herbicide. It is absorbed mainly through foliage and moves toward active growing tissues.

Is paraquat a contact or systemic herbicide?

Paraquat is a contact herbicide with very limited translocation. It causes rapid oxidative damage to treated green tissue.

Is diquat a contact herbicide?

Yes. Diquat is a contact-type Group 22 herbicide with limited movement within plants.

Is glufosinate contact or systemic?

Glufosinate is generally described as contact-dominant or having limited translocation. It requires strong spray coverage and usually performs best on small, actively growing weeds.

Is 2,4-D a contact or systemic herbicide?

2,4-D is a systemic synthetic auxin herbicide used mainly against susceptible broadleaf weeds in tolerant crops and sites.

Is clethodim systemic?

Yes. Clethodim is a systemic grass herbicide that moves toward susceptible grass growing points.

Are all contact herbicides non-selective?

No. Paraquat and diquat are generally non-selective, while bromoxynil, lactofen, and some other contact-type herbicides are selective in labeled crops.

Are all systemic herbicides non-selective?

No. Glyphosate is generally non-selective, while 2,4-D, dicamba, clethodim, and many other systemic herbicides are selective under labeled conditions.

Is contact versus systemic the same as pre- versus post-emergence?

No. Contact versus systemic describes plant movement. Pre- versus post-emergence describes application timing relative to weed emergence.

Is systemic the same as residual?

No. Systemic describes movement within plants. Residual describes continued biological activity in soil or another treatment zone.

Can contact and systemic herbicides be mixed?

Some labels allow such mixtures, but compatibility and performance must be confirmed. Rapid contact injury can sometimes reduce systemic absorption or translocation.

Which type needs better spray coverage?

Contact herbicides generally require more uniform coverage because untreated tissue may remain alive. Systemic herbicides still require an adequate deposit and sufficient absorption area.

Why do weeds regrow after contact herbicide application?

The foliage may die while roots, rhizomes, tubers, or protected growing points remain alive and produce new shoots.

Why can a systemic herbicide appear not to be working?

Systemic symptoms may develop slowly. Poor absorption, stress, rain, low temperature, mature weeds, incorrect timing, resistance, or insufficient translocation can also reduce performance.

Choose by Weed Biology, Not Visible Speed Alone

The contact-versus-systemic decision should follow a practical sequence:

1. Identify the weed species.
2. Determine whether it is annual, biennial, or perennial.
3. Check for taproots, rhizomes, tubers, stolons, or woody structures.
4. Confirm whether fast burndown or regrowth control is the priority.
5. Select an active ingredient effective against the target weed.
6. Confirm the mode-of-action group and resistance status.
7. Verify crop or use-site registration.
8. Evaluate application equipment and coverage requirements.
9. Check environmental and label restrictions.
10. Monitor the treatment for survival and regrowth.

Choose a contact herbicide when rapid above-ground control, desiccation, or management of small annual weeds is the primary objective and the label supports the application.

Choose a systemic herbicide when the program requires movement into growing points or underground tissues, particularly for established perennial weeds.

For importers, distributors, and agricultural brands, the strongest product portfolio does not treat contact and systemic herbicides as competing categories. It positions each type according to weed biology, crop safety, application conditions, resistance management, and local registration.

The final product decision should be based on the complete combination of active ingredient, movement pattern, mode of action, formulation, registered use, and target-market requirements—not on visible speed alone.