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Clethodim didn’t just show up in a flash; its history tells a story about the endless battle between agriculture and weeds. In the 1980s, the search for better post-emergence herbicides pressed chemists to work overtime. Weeds had grown resistant to a lot of earlier chemicals, which were also hard on crops themselves. Research labs rolled out a new family called cyclohexanediones. Among them, clethodim stood out thanks to its ability to hit grasses without damaging typical broadleaf crops like soybeans or potatoes. After a decade of rigorous tests and registration hurdles, it began hitting markets in the early 1990s, shifting weed management on millions of acres. Its popularity taught farmers that specialty herbicides could save not just crops but serious replant costs.
Clethodim comes as a selective, systemic herbicide. In plain language, farmers spray it on their fields, and it moves inside plant tissue to shut down key steps in grass growth. It stops an enzyme—ACCase—that all grass weeds need, crippling their ability to produce new cells at the growing points. For crops that don’t depend on ACCase, like soybeans or peanuts, clethodim keeps fields clear while leaving roots and shoots unharmed. The market sees it mostly as emulsifiable concentrates, designed to mix cleanly with water and stick to plant leaves long enough to soak in. Labels reflect the tight tolerances demanded by regulators to safeguard both users and the environment.
Clethodim doesn’t look all that exciting in a bottle. It brings a faint yellowish tint, with an oily consistency that makes it easy to blend. With a melting point below 70°C and limited water solubility, it needs solvents to get the active ingredient properly mixed for spraying. Molecular-wise, it stacks up as C17H26ClNO3S. Under normal room temperature conditions, it doesn’t break down quickly, but in the field, sunlight and soil microbes begin cutting it apart within days to weeks. Storage rules call for cool, dark places—exposing it to heat or direct sunlight shortens shelf life and can spoil batch quality.
Every bottle or drum of clethodim comes with technical specs set by both manufacturers and regulators. The active content checks in around 92% for technical grade material, with impurities capped in the parts-per-million range to guard against off-target effects. Labels walk applicators through dilution rates, spray volume, and allowable timing—especially pre-harvest intervals to ensure residue levels drop below legal limits for consumers. Safety instructions get a whole section; gloves, eye protection, and enclosed cabs for tractors reflect the compound’s risk profile. Buyers expect barcode labeling, manufacturing batch numbers, and detailed ingredients in line with pesticide regulations worldwide.
The manufacturing path for clethodim combines craftsmanship with industrial scale. It starts from simple carbon chain building blocks, which react with various halides, acids, and sulfur-based groups in a series of carefully sequenced steps. Every reaction needs controlled temperature, pH, and plenty of time for purification. Once the molecule locks into its active shape, bulk processing and quality checks become critical. Modern plants recycle reaction byproducts for environmental reasons and monitor emissions closely to prevent leaks into water or air. Facility teams constantly tweak synthetic routes, aiming to cut costs without sacrificing purity or safety.
Clethodim rarely sits idle once it hits the field. The molecule’s key point is the cyclohexanedione ring, fused to bulky functional groups that block breakdown by weed enzymes. Its chemical backbone lets scientists play with small side chain modifications, creating analogs that can tackle even tougher weeds or survive in different soil conditions. Every new tweak means more hours in the field and the lab, as small changes in chemistry may boost residual effects or speed up breakdown in hot, humid areas. This chemical flexibility keeps it ahead of resistant weed strains—at least, for a while.
Walk through any ag supply store, and you’ll find clethodim bottles sporting a range of names. The main ones stick close to the original—like “Select,” “Centurion,” and “Arrow”—but regional formulations create a long tail of labels. Each country’s rules on generic products pile up synonyms, so buyers might see codes like BAS 51700, or longer IUPAC-style descriptors. This mix of names sometimes causes confusion in global trade, but standardization protocols in major markets help smooth things out for large growers and exporters.
Herbicides like clethodim demand respect during use. Accidental splashes or inhalation can irritate skin, eyes, and lungs, and the compound’s breakdown products linger in soils for days under some conditions. Safety manuals urge users to suit up fully and avoid working on windy days. Drift to non-target fields, especially with windblown sprays, leads to serious legal headaches, so buffer zones and targeted spray nozzles play a big part in application plans. Regulatory agencies periodically review scientific literature, setting residue tolerances that balance weed control needs with risks to farmworkers, wildlife, and the public’s dinner table.
Clethodim’s sweet spot runs through broadleaf crops—soybeans, canola, cotton, sunflower, and veggies like tomatoes and lettuce. These industries face relentless pressure from tough annual and perennial grasses that out-compete cash crops. Earlier weedkillers scorched everything in their path, making selective “grass-killers” prized among growers. Specialty flower nurseries, landscape teams, and seed producers also rely on clethodim to keep beds clear of grassy invaders. With the rise of no-till and low-till farming, which leaves more weed seeds in the soil, demand for selectivity only grows.
Research labs keep poking at clethodim’s chemistry and application tricks. One big topic surrounds weed resistance; some wild grasses have now evolved to block or degrade clethodim, forcing scientists to look at tank-mix ingredients or alternation with other herbicides. Researchers experiment with adjuvants—additives that help the herbicide penetrate waxy leaf surfaces or survive rainfastness. There’s work on nano-formulations, giving smaller droplets better leaf coverage and more reliable absorption. Some studies chase environmental issues, measuring runoff in groundwater and watching for impacts on insects and microbes that form the foundation of healthy soils.
Clethodim lands in the “low to moderate” toxicity bracket on common rating scales—less hazardous than older phenoxy herbicides, but still a chemical that needs careful handling. Acute doses can cause temporary irritation, but the risk of chronic effects seems low at normal field exposure. Toxicologists have checked impacts on mammals, fish, and birds. For most non-target species, only massive overdoses cause problems, yet aquatic organisms show more sensitivity, so avoiding runoff remains a key management goal. Regulators base allowable use on decades of feeding trials, metabolism studies, and ongoing environmental sampling programs.
The story of clethodim doesn’t wind down here. Climate shifts and changing crop genetics set up a moving target for weed pressures. Manufacturers work to stretch efficacy through new formulations, while farmers rotate chemicals to sidestep resistance. The future likely brings stricter limits on residues, heavier requirements for field record-keeping, and more robust surveillance of environmental impacts. Digital tools—GPS-guided sprayers, soil moisture monitors—tighten up application to cut losses and keep fields within legal limits. It’s likely that novel chemistries, possibly building from clethodim’s backbone, will enter the market as scientists stay one step ahead of adapting weeds, striving for cleaner, more reliable food production.
Every spring, there's a big push in many farming communities. At sunrise, engines rev up and sprayers roll out across bean and vegetable fields. Weeds threaten the work of the last planting season, and nothing fights the grassy troublemakers quite like clethodim. This chemical might not have a catchy name, but it packs a punch. Clethodim targets unwanted grasses. That includes stubborn competitors like foxtail, barnyardgrass, and Johnsongrass, which crowd out crops and rob them of water and nutrients.
Most fields in the Midwest hold at least one section overrun with grasses. They showed up after a windy storm or mixed in with last season’s seed. Grasses slip through cracks in weed control routines since many herbicides focus more on broadleaf weeds. Clethodim fills that gap. It breaks down inside grassy weeds, stopping them from building cells the way they need to grow. Soybean and some vegetable plants shrug off clethodim, so the crop keeps growing while the weeds die back.
Spray rigs apply clethodim as a foliar spray, right onto weed leaves. The best time comes when grasses are still young and tender. Bigger, mature weeds hold out longer and may only get stunted. There’s a learning curve with timing and spray coverage. If the weeds outnumber your crop, and they’re getting too tall, clethodim might not save the day. For vegetable growers, clethodim prevents small grasses from spreading through lettuce, carrots, onions, and tomatoes. It gives these specialty crops a chance to thrive where hand weeding just won’t cut it.
Problems start brewing if farmers lean too hard on one herbicide. Weeds adapt—the same way people get used to antibiotics. A few grass weeds survive, and the next season, they grow back even tougher. After decades of heavy use, resistance has cropped up in some places. Farmers need to rotate chemicals and add in some cultural practices, such as crop rotation and using tillage when practical. This slows resistance and keeps clethodim working in the long run.
Clethodim doesn’t usually harm wildlife or water if people use it as instructed. The EPA says it has a fairly low risk profile compared to older herbicides like paraquat, provided workers follow label recommendations. For farm families, this means mixing and spraying with gloves, closed-toe shoes, and a wash-up at the end of the job. People share stories in rural communities of headaches or rashes if they skip safety steps, which turns into a cautionary tale for new workers.
Clethodim makes a big difference in the battle against grassy weeds. Farmers know its value, but also its limits. Staying prepared with more than one weed control plan and paying attention to resistance keeps fields productive. As weed science continues to adapt, clethodim stands as one tool in a much larger toolbox. Keeping food production strong for everyone means treating every tool with care and respect.
Farmers know grass weeds can ruin a crop season. Clethodim steps up as a reliable fix, especially in broadleaf crops. Walk through a soybean or canola field fighting foxtail or crabgrass, and the difference after applying clethodim stands out. You see clear rows again because the grasses die back, leaving the main crop to thrive.
Clethodim belongs to a group called “DIM” herbicides. It doesn’t touch broadleaf plants but stops annual and perennial grass weeds cold. Its design means it works inside the plant. After spraying, grasses absorb it through their leaves. The active molecule travels to growing points and shuts down an enzyme called ACCase—short for acetyl-CoA carboxylase. This enzyme makes fatty acids, which help build cell membranes and keep grasses alive. Without new fatty acids, grass weeds can’t grow and start to wither after a few days.
Every year, farm operators face the issue of certain herbicides losing power. Weather and resistance shift weed dynamics. Clethodim’s specific enzyme target means it fills a gap where older weedkillers fall short. It has real value in fields planted with crops like soybeans, peanuts, or sugar beets, since these broadleaf crops carry a natural tolerance to the chemical—so you hit the grasses, not the main crop.
Farmers check grass growth stage and weather before using clethodim. Sunny, active-growing conditions mean weeds take up the herbicide faster, and activity increases. It helps to add an oil-based adjuvant to the spray tank so the plant’s waxy surface doesn’t block absorption. Mixing partners matter, too. Clethodim can get along with some common tank-mix partners, but mixing with herbicides that don’t get along (like certain broadleaf weed killers) degrades its effect.
Continuous heavy use of one type of control carries risk. Resistant grass weeds like Italian ryegrass started popping up where folks leaned too hard on ACCase-inhibitors. Resistance builds slowly at first, then can spiral. In my work, I’ve seen whole patches of fields where clethodim no longer knocks back ryegrass, forcing growers to use expensive hand-weeding or flip crop choices the next season.
Clethodim stands out as a tool, but it’s not a silver bullet. Responsible herbicide choice hinges on rotating modes of action. Mixing it up keeps resistance at bay longer. Most agronomy guides suggest combining clethodim with cultural practices: change planting dates, rotate crops, and use cover crops or tillage where it fits the system.
Safety for applicators and neighbors also counts. Clethodim won’t drift far, but handlers need to wear gloves and avoid breathing in any mist or vapor. Rinsing out gear and storing leftovers safely—this keeps accidents down and water clean.
For me, clethodim illustrates how a single-mode herbicide can protect yields and boost food security, as long as folks respect its limits and resistance risk. Keeping this tool working for future seasons calls for sharp eyes in the field, solid records, and talking regularly with crop advisors. There’s no shortcut here—getting the basics right keeps farm systems productive for everyone.
Clethodim is a real workhorse for growers fighting grassy weeds. The folks who work tired soil patches, or anyone who’s seen johnsongrass choke out new soybean shoots, already know weeds don’t just steal nutrients; they strip away profit and hard-earned hope for a good harvest. Clethodim answers a real need for a post-emergence, selective way to zero in on those tough grasses and leave broadleaf crops alone.
Clethodim carries EPA backing for many broadleaf crops that anchor North American agriculture. Soybeans and cotton are the two heavyweights. Both crops handle clethodim in the field with no obvious stress under normal label rates. Farm records and university trials keep pointing to this reliability: soybeans, cotton, peanuts, field beans, alfalfa, and field peas all fit comfortably in the “safe” category. Dry edible beans, potatoes, canola, and flax make that list as well. You also see clethodim in ornamental plant nurseries and on certain root vegetables. Anybody unsure about their specific crop should check the clethodim product label from their supplier, since minor uses and state-by-state approvals differ.
These broadleaves get along with clethodim because they process it differently than grasses do. Clethodim targets an enzyme that grasses need for growth. Broadleaf crops either don’t rely on this enzyme or have enough tolerance to handle the right dose. Decades of use show that soybeans, peanuts, alfalfa, and canola weather clethodim treatments with no stunt or yellowing under usual field conditions.
Corn, wheat, barley, rice, and other cereal grains can’t tolerate clethodim. Their enzyme pathways fall apart once exposed. No one wants to see a cornfield yellow and die off by accident after a drift. Many forage grasses and pastures fall into the same “do not spray” category, unless a total field kill is the goal before a crop change. Always double-check both the product label and seed variety—newer herbicide-tolerant crops keep arriving, but the wrong decision costs time and money.
Growers know that no field stays uniform year in and year out. Weather swings, crop rotation, new weed species, and supply shortages show up without warning. Clethodim works best as one tool in a bigger toolbox. University extension bulletins urge folks to rotate herbicides, keep coverage consistent, and avoid spraying during wind or right before rainfall. Walking the rows and checking for off-target symptoms on neighboring crops gives early hints if something goes sideways.
I’ve spoken with more than a few farmers who’ve struggled with resistant foxtail and crabgrass in established alfalfa. Clethodim can turn those problem patches around, provided it’s in a rotation plan with non-chemical controls—cover crops, careful tillage, and not repeating the same herbicide every year. If regulations or market shifts knock clethodim out of the toolbox, agronomists encourage crop diversification and scouting for trouble long before you see weed seed heads waving above the canopy.
As cropping systems shift, and technology brings forward new herbicide-tolerant seed traits, clethodim’s fit in weed control programs still matters. Long-term stewardship, field scouting, solid record-keeping, and using clethodim on approved broadleaf crops all balance harvest goals with respect for soil, water, and the next crop in the rotation.
Clethodim steps in as a post-emergence herbicide aimed at controlling grassy weeds in broadleaf crops. Folks working with soybeans, canola, peanuts, and potatoes have probably run into clethodim before. Its selective action against grasses makes it especially helpful for mixed fields. While the label on the bottle always serves as the legal starting point, real-world results often depend on both label guidance and practical experience.
Most labels in North America recommend clethodim at 4 to 8 fluid ounces per acre (about 120-240 mL/acre) for annual grasses. Tougher perennial grasses, like rhizome johnsongrass, usually require closer to 16 fluid ounces (475 mL/acre). This range isn’t just manufacturer caution—it’s about recognizing the type and stage of the weeds. I’ve seen folks shave rates to save a dollar, only to face a mess when late flushes escape control. Weeds past four inches in height or in drought-stressed fields often shrug off low rates.
Clethodim works best when paired with adjuvants. Crop oil concentrate at a rate of one percent by volume stands as the gold standard, making sure the herbicide sticks and gets into the weed. Some extension services suggest adding ammonium sulfate, especially in hard water areas, to boost performance. That extra detail shows up in university trials, too: the right adjuvant combo can double the control on tough grasses like foxtail and volunteer corn. Surfactant choices make a real difference. I’ve learned that skimping on oil or mixing with the wrong formulation limits clethodim’s punch.
No herbicide handles every season or every crop mix. Early morning, with plants actively growing and dew on the leaves, you’ll see better results than spraying in the afternoon during a hot, dry wind. Rain within an hour after spraying? Plan on lost effectiveness. Clethodim requires at least an hour of dry weather for full uptake. And even though clethodim breaks down fairly quickly, re-entry intervals and pre-harvest guidelines must be respected. Cutting corners might save time but sets up resistance issues down the line.
Sticking with the recommended rate stems from more than just following instructions. Too little herbicide doesn’t just let weeds escape—it drives resistance. Grasses like barnyardgrass and Italian ryegrass are already showing tolerance in some areas. Surviving plants pass on genes that make future control harder. Over-reliance on clethodim for volunteer corn control in soybeans has kicked up resistance in the Midwest. A neighbor of mine learned this lesson the hard way: a low rate one season led to a lot more trouble dealing with grassy escapes for three years after. Stewardship really counts.
Understanding the local weed pressure comes first. Take the time to scout and identify what’s coming up. Stick to the recommended rate on the label, adjusting upward in heavy pressure or for older weeds. Rotate modes of action to limit resistance. Keep records on what’s sprayed and what the field looks like after. That diary of spray dates, rates, and weather conditions often offers more insight than any product flyer. Tap into extension specialists if you’re uncertain. Their trials often show nuances not found in national recommendations.
Applying clethodim at the recommended rate isn’t just about following rules. It preserves the tool for future seasons, saves time and money in the long run, and supports sound stewardship of the land. Anyone who wants clean fields and fewer headaches down the line pays close attention not only to the label, but to what’s happening on the ground—and in their local weed communities.
Clethodim has become a common go-to for folks dealing with annual and perennial grass weeds throughout the growing season. As a selective herbicide, it finds a home on vegetable farms, soybean patches, and orchards. Its working power can’t be ignored, but neither should the risks tied to careless handling. I’ve worked around similar products for years, and overlooking safety—even once—can argue with your skin, your lungs, or worse. The importance lies in the little details that shape each workday, from the way you open the jug to the way you wash up before dinner.
I never reach for clethodim without pulling on gloves—nitrile or neoprene usually last through a long day. Regular latex breaks down too easily, and chemicals can slip through unnoticed. Cotton shirts and long pants stop the spray from finding its way to your skin. Between the cuffs and collar, I keep a snug fit, so nothing drips down my arms. Rubber boots finish the look, since wet shoes don’t wash clean, and you don’t want residues walking into your home.
Pouring or mixing clethodim turns routine jobs risky in a hurry. I use a funnel for transfer, to slow things down and avoid splashes. Even if you’re careful, the container’s rim almost always gets sticky, so I rinse it right away. Eye protection sits on my nose before the cap comes off, because splashing chemicals in your eyes sends you straight to the ER. Mixing tanks at the right height keeps you from lifting buckets above your face—a lesson you remember after only one bad spill.
Respiratory masks start to feel awkward after a few hours, especially in summer, but skipping them courts throat and lung irritation, sometimes headaches. Even outdoors, fine mists can hang in the air if there’s no wind. Every label spells out the rate and mixing instructions for a reason; using more doesn’t give better weed control, just bigger problems—crop injury, environmental drift, and harder clean-up later.
Once you finish spraying, washing up isn’t optional. Hands, face, and exposed skin all need a good scrub, not just a quick rinse. That’s how you keep clethodim out of your eyes and mouth without thinking about it. Work clothes go straight into the wash, never mixing with regular laundry. Even one contaminated shirt brings herbicide home to family members, especially kids.
Leftover product and empty containers cause temptation to cut corners. I’ve seen plenty of folks use empty containers for non-farm jobs. That decision turns dangerous quickly. Every piece of gear and every bucket gets triple rinsed with clean water. Spent containers need puncturing before heading to a disposal site authorized for farm chemicals, not a regular landfill.
The U.S. EPA keeps clethodim classified as a low-to-moderate risk chemical when handled right. That allowance comes from plenty of field and lab testing backing safety, but only for workers who follow label guidance. Skin rash, headaches, or worse, triggered by shortcuts, end up costing more time and health than a moment's caution.
Practical safety isn’t just for big farms or commercial applicators. Anyone handling clethodim—no matter their acreage—plays a role in protecting their own health, neighbors, and land. Reading every new batch’s label, checking safety gear, and respecting the clean-up all put you ahead. Sound safety steps do more than keep trouble out of reach; they keep you on the job and at home for the season’s ups and downs.
| Names | |
| Preferred IUPAC name | (5RS)-2-[(1E)-1-[[2-(Ethylsulfanyl)propyl]sulfanyl]ethylidene]-5-(2-methoxyprop-2-yl)-3-hydroxycyclohexan-1-one |
| Other names |
Centurion Select Prism Arrow Clethodin Topik Envoy Shogun |
| Pronunciation | /ˈklɛθ.ə.dɪm/ |
| Identifiers | |
| CAS Number | 99129-21-2 |
| Beilstein Reference | 1643005 |
| ChEBI | CHEBI:9585 |
| ChEMBL | CHEMBL56630 |
| ChemSpider | 103015 |
| DrugBank | DB16557 |
| ECHA InfoCard | 13c7538d-9a77-4d85-a935-997a5b8d1b47 |
| EC Number | EINECS 433-450-1 |
| Gmelin Reference | 92636 |
| KEGG | C11312 |
| MeSH | D000068878 |
| PubChem CID | 69192 |
| RTECS number | RG8225000 |
| UNII | 9N08U3C06T |
| UN number | UN 3082 |
| Properties | |
| Chemical formula | C17H26ClNO2S |
| Molar mass | 277.8 g/mol |
| Appearance | Clear, colorless to pale yellow liquid |
| Odor | Mild ether-like odor |
| Density | 0.993 g/cm³ |
| Solubility in water | Soluble |
| log P | 3.41 |
| Vapor pressure | 1.8 x 10⁻³ Pa (25 °C) |
| Acidity (pKa) | pKa = 4.43 |
| Basicity (pKb) | 12.3 |
| Refractive index (nD) | 1.493 |
| Viscosity | Viscosity: 2.4 mPa·s |
| Dipole moment | 4.34 D |
| Thermochemistry | |
| Std molar entropy (S⦵298) | 371.9 J·mol⁻¹·K⁻¹ |
| Std enthalpy of formation (ΔfH⦵298) | -173.6 kJ/mol |
| Std enthalpy of combustion (ΔcH⦵298) | -6864 kJ/mol |
| Pharmacology | |
| ATC code | QH03AX23 |
| Hazards | |
| GHS labelling | GHS02, GHS07, GHS08 |
| Pictograms | GHS02,GHS07 |
| Signal word | Warning |
| Hazard statements | H226, H304, H317, H319, H332, H335, H411 |
| Precautionary statements | P201, P202, P261, P264, P270, P273, P280, P301+P312, P308+P313, P314, P405, P501 |
| Flash point | 79°C |
| Autoignition temperature | Approximately 399°C |
| Lethal dose or concentration | Lethal Dose (LD50) Oral (rat): 1620 mg/kg |
| LD50 (median dose) | LD50 (median dose) of Clethodim: "1,630 mg/kg (oral, rat) |
| NIOSH | URK84300AJ |
| PEL (Permissible) | 0.1 mg/L |
| REL (Recommended) | 0.1 |
| IDLH (Immediate danger) | Not established |
| Related compounds | |
| Related compounds |
Cycloxydim Sethoxydim Butroxydim |
