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Agricultural scientists have always searched for better ways to tackle weeds without harming the crops people depend on. In the late twentieth century, researchers across Asia invested in new classes of herbicides as large-scale farming claimed more land and weeds threatened yields. Pyrazosulfan grew out of this hunt for safer, more precise weed control. Originally developed by Japanese chemists trying to answer the need for paddy-safe selective herbicides, it entered the market with a promise: it would target troublesome grassy and broadleaf weeds in rice paddies, sparing both rice and other aquatic life. Its introduction went hand-in-hand with changing rules about environmental safety and the shrinking tolerance for older chemicals known to linger in the soil and water.
Most fields coated in Pyrazosulfan today show fewer tough weeds without the patchiness or crop yellowing people worried about with older compounds. The molecule owes its power to its ability to disrupt plant-specific processes at the biochemical level, meaning weeds with certain enzyme structures fail to grow, but rice pulls through seemingly untouched. Most commercial products containing Pyrazosulfan get used as either wettable granules or suspensions. They dissolve evenly in irrigation water, making it simple for farmers to cover rice fields after transplanting. Companies distribute these products across Asian agricultural regions, usually combining Pyrazosulfan with agents that help it spread and stick in waterlogged soils.
In its pure form, Pyrazosulfan appears as a white to off-white powder, carrying little to no noticeable odor. It does not dissolve well in water at room temperature, but manufacturers blend it with surfactants so it spreads efficiently across damp surfaces. The molecule shows high stability in both acidic and neutral pH environments. At high temperatures, it can start to break down, so storage must stay cool and dry. Pyrazosulfan's molecular structure features a sulfonylurea backbone with a pyrazole group, which serves as the business end of its weed-fighting action. This unique build makes it resistant to fast degradation, so a single treatment lasts throughout the main weed germination stage.
Labels on Pyrazosulfan products always list the active ingredient content, usually given as a percentage by weight. Most products contain between 10% and 25% active molecule, with the rest made up of stabilizers and wetting agents. Tank mix instructions urge users to follow precise application rates—typically between 10 and 30 grams per hectare—since overdosing not only wastes money but can push residue limits beyond legal thresholds. Instructions stress the importance of evenly distributing the product in standing water shortly after rice transplanting, as this timing crushes weeds before they gain a foothold. Manufacturers print batch numbers and manufacturing dates for traceability, which helps both farmers and authorities keep tabs on product origin and quality.
Pyrazosulfan production starts with carefully chosen aromatic starting materials, run through a series of sulfonation, cyclization, and urea coupling steps. Chemical engineers pay special attention to purity at each stage, removing byproducts with meticulous solvent washes and filtration steps. Final purification relies on repeated recrystallization, pulling the active substance away from related contaminants and unused starting material. Facilities that turn out Pyrazosulfan for the big agrochemical brands tend to possess modern quality labs, analyzing every batch with chromatography and spectroscopy—tools that guarantee every dose remains within the narrow purity window set by national regulators. Waste from the production process, including solvent and wash water, demands careful neutralization and disposal to avoid polluting the communities near factories.
Pyrazosulfan includes reactive sulfonamide and urea moieties that allow for certain modifications, though the base herbicidal effect remains tied to this structure. Synthetic chemists in R&D labs sometimes attach different groups to the aromatic rings to produce analogues with altered weed spectra or breakdown rates for special climates. Labs have pushed these tweaks while retaining the critical pyrazole-sulfonylurea linkage, aiming for broader weed coverage or quicker breakdown in soils where residue worries run high. The molecule itself can hydrolyze under strong acid or alkaline conditions, which rarely occurs in paddy fields but becomes critical during product disposal or accidental spills, as improper cleanup could trigger unwanted breakdown products.
In research papers and shipment manifests, Pyrazosulfan sometimes appears as its common trade name or with less familiar chemical synonyms, such as N-[(4,6-dimethoxypyrimidin-2-yl)aminocarbonyl]-5-(4,6-dimethoxy-2-pyrimidinylamino)sulfonyl-1-methylpyrazole. In practice, seed and fertilizer dealers stick to registered trademarks, often including ‘SU’ in the trade name to highlight the sulfonylurea root. No matter the name, regulators insist any derivation of the molecule meets the reference standard’s purity, toxicity, and breakdown profile before reaching the public. Crop advisers stay aware of synonym lists to avoid supply chain mix-ups, especially when pyrazosulfan-based products cross borders.
Exposure guidelines and handling protocols for Pyrazosulfan put worker safety at the top of the list, primarily because, despite its selectivity, long-term or high-concentration contact affects non-target species, including humans. Farmers wear gloves, masks, and waterproof aprons while mixing and loading the granules, especially during windy days when dust could float. Product storage stays locked and well-ventilated, away from food and animal feed, to prevent accidental ingestion. Any spill or tank cleaning water gets collected for approved disposal, usually through licensed waste management services. Agricultural extension workers regularly teach best practices, emphasizing handwashing, label reading, and timing applications so residues don’t drift beyond field boundaries into streams or homes.
Pyrazosulfan’s best-known use centers on rice paddies, mainly in regions like Japan, Korea, and parts of China where standing water dominates early rice development. Here, it checks weed species that rob nutrients and crowd out rice seedlings, helping raise harvests and steady incomes for farm families. The molecule also sees some off-label attention in test plots of wheat and barley, though such use typically awaits further regulatory clearance. Research groups in tropical countries keep running trials to see how Pyrazosulfan fares against emerging weed threats as shifting climate and planting calendars alter weed biology. Each season, hundreds of thousands of hectares rely on Pyrazosulfan to help rice seedlings outpace weeds, especially where labor shortages make traditional hand-pulling unrealistic.
Academic and corporate R&D teams run ongoing field trials and laboratory assays, not just to verify weed control but to check soil persistence, crop tolerance, and water runoff. Universities continue screening for potential weed resistance and developing new application methods that cut chemical use without giving up weed suppression. Most recently, gene sequencing in weeds revealed possible marker genes indicating resistance before it spreads, driving research toward tank mixes and rotations that slow down this adaptation. International R&D consortia share data on environmental fate, getting input from water conservationists and biodiversity advocates who study paddy systems. Such collaboration has led to improved application devices—tools that deliver exact doses only where needed, protecting neighboring wild areas.
Toxicologists keep close tabs on Pyrazosulfan’s effects across organisms, measuring how much stays in food, water, and the environment after normal use. Acute toxicity studies in mammals show that the molecule only poses real harm at doses far above those seen from farming applications, though eye and skin irritation do occur with careless handling. Chronic studies raise more complex questions about what repeated low-level exposure means for farm workers and wildlife over decades. Lab tests with fish and amphibians shape water management guidelines for rice paddies, helping authorities ban overspraying near sensitive habitats. Regulators insist on regular food-crop residue testing—a step public health officials see as crucial for long-term safety in markets where rice forms the staple meal.
Looking forward, the future of Pyrazosulfan connects to both farming needs and tightening rules around environmental exposure. Research points to new delivery systems—coated seeds, time-release granules, and precise spray robots—that could drop the active ingredient right where weeds start without dosing the whole field. Expect pressure for “green chemistry” alternatives to speed up as society demands quicker breakdown times and smaller ecological footprints. Big questions remain about how changing climate, international trade, and evolving weed populations will challenge both Pyrazosulfan and the companies that make it. Industry and research communities have no choice but to adapt, learning from today’s paddy fields to build safer, more effective ways to feed an increasing population without sacrificing local ecosystems.
Farming doesn’t work without some help from science, especially with more mouths to feed and land stretched thin. Pyrazosulfan falls right into that intersection of chemistry and growing food. This herbicide, built from the sulfonylurea group, gives rice farmers a new way to fight weeds that can ruin a season’s work before it’s even started. Weeds have a way of bouncing back. Hit them with old herbicides, and some just shrug it off. Pyrazosulfan offers a different approach. Over the past decade, I’ve watched the scramble for newer herbicides each year—each one promising to work where the last one let farmers down. Pyrazosulfan stands out because it targets broadleaf weeds and sedges that traditional products sometimes miss.
Weeds are more than just a nuisance. Competing for sunlight, water, and nutrients, they sap energy from the rice crop. If you’ve ever stood in a field after a poor spray round, the sight of tangled grass and stunted stalks leaves no doubt that losses are real. Pyrazosulfan is designed for pre-emergence use, which means it goes down before the weed seedlings even have a shot. This catch-them-early strategy changes outcomes because the weeds don’t get a head start. In field trials across Asia, experts saw improved yields when Pyrazosulfan took over from less effective herbicides. Unchecked, weeds can take away a quarter or more of the possible harvest.
Farm hands aren’t unlimited, nor is time. Switching to a product that lasts longer in the soil gives farmers an edge. Pyrazosulfan lingers just enough to keep new flushes of weeds from sprouting, but not so long that it threatens the next crop rotation. As someone who’s helped test treatments through a crop season, seeing farmers need fewer re-sprays means more time for other jobs around the field—and less money spent overall.
It’s worth mentioning that Pyrazosulfan works at very low rates, usually a few grams per hectare. Lower doses mean less chemical flowing through waterways, which researchers keep a close eye on. Big chemical loads in the soil don’t help anyone—not the world’s food supply, and not the people working the fields. Environmental scientists spent years running residue studies before this herbicide reached market shelves. In every region, local authorities set limits and require research to back up each new label claim, drawing on lessons from years of overuse or drift with older products.
No “magic bullet” exists in weed control. Pyrazosulfan must get rotated with other herbicides and combined with non-chemical approaches if farmers want to dodge resistance. I’ve seen the warning signs: fields where nothing works anymore, and farmers start over from scratch. The answer isn’t using more chemicals but using the right mix, paired with smart timing and scouting. Extension agents and scientists play a big part in teaching this, and the message has to stick—one good harvest doesn’t guarantee the next.
Access to safe, effective herbicides like Pyrazosulfan keeps farmers in business and keeps food on the table. As climate changes, and as weed patterns shift, those in ag science can’t sit still. Adapting, learning, and updating advice keeps farms ahead of weeds, not caught off guard.
Pyrazosulfan stands out for farmers who juggle weed pressure and the constant challenge of achieving cleaner rows. Herbicides built on sulfonylurea chemistry like this one have offered a strong punch over the years against stubborn broadleaf and sedge weeds. Success with any active ingredient in the field comes down to whether people understand how much to use and on which crops it actually pulls weight.
Advice floating around from universities and manufacturers generally puts pyrazosulfan in the range of 30 to 50 grams active ingredient per hectare. Rates depend on your weed problem and the type of soil. Sandier soils with less organic matter soak up herbicides differently than clay-heavy ground. Go too low and patchy control often follows. Swing too high with dose and friendly crops can suffer, which only adds cost and re-sowing headaches nobody wants.
For rice, which remains the key crop for this herbicide in Asia, field research from institutions like IRRI recommends staying closer to 40 grams per hectare pre-emergence, especially since young rice seedlings can be sensitive. Dry direct-seeding or wet transplanting both respond well to the pre-emergence timing, as weeds are stopped before they break through the soil. A single spring application after planting usually does the trick for paddies, as long as water management stays consistent.
Farmers growing rice have seen the most consistent returns from pyrazosulfan. This chemistry lines up well with wetland crops, blocking sedges, nutsedges, and many broadleaf intruders without stopping rice growth in its tracks. Some trials have explored use in wheat and barley, though regulatory labels lean far more toward paddy fields.
Corn, soybeans, and vegetables haven’t gained the same level of support from trials or government approvals. Most extension offices stick with rice as the headline crop, which fits the data seen in field observations. Pyrazosulfan acts on the ALS enzyme, a target rice tolerates due to its growth habits and other inbuilt defenses. Off-label use in less tolerant crops can cause setbacks that last a whole season. Sticking to crops and rates supported by research cuts back on crop loss and keeps resistance from building up in local weed populations.
Smallholder rice farmers in China and Vietnam have reported fewer hand weeding hours and bigger final yields thanks to including pyrazosulfan in rotation. Yield boosts of 5 to 8 percent pop up in field surveys, tied directly to cleaner rows and a strong start in the early weeks. Combining this herbicide with a good pre-plant fertilizer plan works best for most. Overuse, poor timing, or using it too many seasons in a row bring problems like resistance and non-target damage. Reports from Japan and the Philippines point out certain Cyperus weeds starting to shrug off treatments if the same program runs every spring.
Rotating chemical groups builds a stronger, longer-lasting weed program. Pulled from personal experience walking through paddy fields each summer, mixing up the herbicides from different classes keeps the weeds guessing. Sharpening water and fertilizer management, making side-by-side comparisons of different modes of action, and listening to extension field trial advice—these steps promise longer-term success.
Choosing the right rate for the crop, watching for weather changes, and checking the label and local guidance every year go a long way toward protecting yields. Pyrazosulfan plays its best hand as part of a bigger plan, not as a catch-all. In a world where new weeds show up every rainfall, practical, well-informed decisions make all the difference.
Farmers and growers always look for ways to protect crops without harming the soil, water, or wildlife around their fields. Pyrazosulfan steps into the mix as a selective herbicide, targeting unwanted plants while leaving valuable crops untouched. My own time spent on family farms showed me how even one bad weed season can ruin a year’s hard work. Tools that help balance productivity and long-term sustainability matter a lot out here.
Pyrazosulfan works inside the weed, blocking a key enzyme responsible for essential amino acid creation. This group of herbicides, known as ALS inhibitors, does not go after every plant. Sensitive species wilt first, while tolerant crops stay healthy. That selectivity brings peace of mind to growers who want cleaner fields but fear damaged harvests.
On our small plots of corn, common weeds like barnyardgrass and broadleaf signal the constant fight we face. Pyrazosulfan stands out because it enters the plant through both the leaves and the roots. Early application gives it a head start, making life harder for weeds just as they sprout. From my experience, catching weeds early always makes for easier management later on.
Chemicals always come with questions. Farmers ask if the tool poisons waterways or lingers in the earth. Studies have measured how pyrazosulfan breaks down and how its byproducts behave. Research from agricultural universities points to low leaching potential and rapid breakdown by soil bacteria. That reduces risks to groundwater and non-target species. Neighbors who raise bees or cattle share real concern about runoff. Thankfully, proper use and mindful application timing lower those risks.
In my experience, weeds learn to dodge repeated attacks. Over time, resistant populations develop if one chemistry gets used too often. The best growers build rotation plans, mixing up herbicides and including physical controls like tilling or cover cropping. This variety stands as the main defense against resistance.
From what I’ve seen, education makes a huge difference. Farmers who understand product labels, weather impacts, and spray timetables show better results and less risk of mistakes. Extension agents, workshops, and plain-language guides help spread the word. In my part of the countryside, shared knowledge helps everyone make smarter decisions for the land and the next generation.
Those who care for crops face a tough job—feeding people while protecting local ecosystems. Pyrazosulfan offers one tool among many, not a silver bullet. Sound management combines new chemistry with time-tested wisdom: respect dosage limits, monitor for resistance, rely on local advice, and never stop learning. By reading, sharing stories, and asking hard questions, communities make better choices in an often unpredictable world.
Ask anyone working in agriculture and most will tell you about the constant battle with weeds. Pyrazosulfan, a herbicide designed to manage these unwanted plants, hit the scene with promises of crop safety and better harvests. It helps rice farmers keep fields productive and control costs—two important goals for an industry that feeds millions.
Years of studying agricultural chemicals taught me that questions around safety go far deeper than labels on packaging. Farmers, fieldworkers, and nearby communities all want to know if contact with something like pyrazosulfan puts them at risk. Testing conducted in Japan and Europe showed that exposure within recommended levels did not cause immediate harm such as rashes or breathing trouble. No strong evidence linked short-term exposure to cancer or genetic damage in humans.
Scientifically, pyrazosulfan does not accumulate much within the body or linger long after exposure. The United Nations Food and Agriculture Organization found its breakdown products clear from soil and crops within a few weeks, which gives some relief. But as someone who’s helped adult learners in rural communities read safety sheets, I know written instructions do not always match the way things play out in the field. Protective gear might stay in the shed on hot days, or warnings about wind direction get ignored when the clock is ticking. That makes straightforward rules on safety critical.
Where chemicals go after leaving the field always concerns me. Rivers and ditches collect runoff, and the same chemical that wipes out weeds in fields can harm plants living in nearby water. The European Food Safety Authority (EFSA) found that pyrazosulfan degrades fairly quickly in wet conditions, which reduces risks to fish and aquatic insects. Still, water sampling in Japan picked up traces after heavy rainfall, showing some gets away from the target fields.
I grew up near a river where summer meant frogs and dragonflies everywhere. Local farmers learned that a single pesticide spill wiped out all the tadpoles one year. That story sticks. Safety reviews stress the importance of buffer zones: strips of grass or wildflowers between fields and water. These barriers help trap chemicals before they reach streams, and they offer a safe haven for bees and birds.
Real-world safety depends on clear labeling, regular worker training, and honest updates about risks as new data emerges. Companies must invest in community outreach. Letting farmers test out less toxic weed controls, like companion planting or modern mechanical weeders, brings new tools to the field. Crop rotation and reducing overall herbicide use cuts down on the build-up of any one chemical.
Nobody wants to undo decades of progress in food security. Consumer demand for clean water and healthy food keeps pressure on regulators and manufacturers. Signing up for community water testing or learning about the field’s crops can make a real difference. Better choices now shape the future—a lesson every generation in farming learns, one season at a time.
Pyrazosulfan stands out in crop protection for its weed-fighting strength, but its safety profile deserves real attention. Stories from seasons in the field remind me that the strongest chemicals often demand the most respect. Pyrazosulfan affects living cells—even a splash on skin feels different from a bit of rainwater, and breathing it in while mixing up a spray batch quickly leads to coughing or a sore throat. These aren't vague warnings. The chemical may trigger respiratory symptoms and skin irritation, and it doesn’t take much for trouble to start. Safety data sheets back this up, linking exposure to headaches, nausea, and, with long contact, more serious health risks. Keeping this compound far from bare skin, eyes, and mouth becomes second nature for anyone who’s spent time applying it.
Old-timers on the farm will never skip gloves, goggles, and a well-fitting mask when handling Pyrazosulfan—lessons come quickly to anyone who’s tried mixing it barehanded. Sturdy rubber gloves keep skin clear of chemicals and keep hands steady for long mixing jobs. Tight safety goggles or a clear face shield keep splashes from eyes, a spot on the face that stings quickly. Many rely on long sleeves, thick pants, and rubber boots, treating every application as if an accident could always happen. Protective equipment works best if it’s checked for holes and cleaned after every use, so it’s reliable next time.
Storage plays a key role in safety. Pyrazosulfan shouldn’t rest on just any shelf or next to livestock feed; it needs a dry, locked cabinet with good ventilation. Damps ruins not just the packaging but the chemical inside, making spills more likely and weakening its effect in the field. Unpredictable temperatures damage containers—heat warps plastic, cold leaves frost on labels, and each change raises the risk of leaks or contamination.
In my experience, a separate cabinet for agricultural chemicals keeps accidents out of the house and barn. The best setups stand high above reach of kids and pets, with clear labels in strong colors—no mix-ups with fertilizer or rodent poison. Pyrazosulfan can react with acids, oxidizers, and strong alkalis, and insurance calls spike after a bad chemical mix. Stories circulate about someone who skipped the sorting and lost half a shed to strange fumes. Keeping original containers, never mixing old leftovers, and not refilling smaller bottles have become rules written in memory, not just on paper.
Safety continues long after application. Leftover Pyrazosulfan and used containers cannot follow trash to a landfill or empty down a drain—local regulations demand hazardous waste disposal. Spills test nerves, especially when powder or granules touch bare ground or trickle into waterways. Shovel or sweep into strong, durable bags, sealed tight for pickup by waste contractors who know their business.
Strong safety standards grow through routine, training, and honesty about the dangers. Every farm crew I’ve worked with checks spill kits, labels, and locks before the season kicks off. This protects not only workers but also the land—accidental misuse poisons more than one harvest. Local extension agents offer workshops and advice, with tips grounded in science and community trust. In the rush of planting, shortcuts tempt everyone, but the stories of harm show that respect for chemicals like Pyrazosulfan isn’t just a policy—it’s a way to move through the season with confidence and care.
| Names | |
| Preferred IUPAC name | N-[(4,6-dimethoxypyrimidin-2-yl)carbamoyl]-2-(1-methyl-1H-pyrazol-4-yl)benzenesulfonamide |
| Other names |
NC-319 Pyrazosulfanum |
| Pronunciation | /paɪˌræz.oʊˈsʌl.fæn/ |
| Identifiers | |
| CAS Number | “119476-01-6” |
| 3D model (JSmol) | `3D model (JSmol)` string for **Pyrazosulfan**: ``` CCOC(=O)C1=CC=NC(NC2=CC=CC(S(N)(=O)=O)=C2)=N1 ``` *(This is the SMILES string representing the 3D structure that JSmol can read.)* |
| Beilstein Reference | Beilstein Reference 5220460 |
| ChEBI | CHEBI:86222 |
| ChEMBL | CHEMBL2104721 |
| ChemSpider | 22371207 |
| DrugBank | DB11723 |
| ECHA InfoCard | 03e17aa2-5972-4b11-99cf-5fe6ed3e848d |
| EC Number | 83411-70-7 |
| Gmelin Reference | 631778 |
| KEGG | C18523 |
| MeSH | D064847 |
| PubChem CID | 10152094 |
| RTECS number | GZ1950000 |
| UNII | KXW9PY60YJ |
| UN number | UN3077 |
| Properties | |
| Chemical formula | C15H16N4O5S2 |
| Molar mass | 474.549 g/mol |
| Appearance | White solid |
| Odor | Odorless |
| Density | 1.41 g/cm3 |
| Solubility in water | 18.7 mg/L (20 °C) |
| log P | 0.82 |
| Vapor pressure | 2.71 × 10⁻⁶ mPa (25°C) |
| Acidity (pKa) | pKa = 4.59 |
| Basicity (pKb) | “pKb = 3.56” |
| Refractive index (nD) | 1.617 |
| Dipole moment | 3.98 D |
| Thermochemistry | |
| Std molar entropy (S⦵298) | 287.8 J·mol⁻¹·K⁻¹ |
| Std enthalpy of formation (ΔfH⦵298) | -124.2 kJ/mol |
| Std enthalpy of combustion (ΔcH⦵298) | -814 kJ mol⁻¹ |
| Hazards | |
| Main hazards | Harmful if swallowed. Causes serious eye irritation. |
| GHS labelling | GHS02, GHS07, GHS09 |
| Pictograms | GHS07,GHS09 |
| Signal word | Warning |
| Hazard statements | H302, H315, H318, H410 |
| Precautionary statements | P261, P264, P270, P272, P273, P280, P301+P312, P302+P352, P304+P340, P305+P351+P338, P312, P330, P363, P391, P501 |
| NFPA 704 (fire diamond) | 2-1-0 |
| Lethal dose or concentration | Oral rat LD50 >2000 mg/kg |
| LD50 (median dose) | LD50 (median dose): 2000 mg/kg |
| NIOSH | No data |
| REL (Recommended) | 40 g a.i./ha |
| Related compounds | |
| Related compounds |
Pyrazosulfuron-ethyl Bensulfuron-methyl Cyclosulfamuron Imazosulfuron |
