The best lawn weed killer for most homeowners is a selective broadleaf herbicide — a blend built on 2,4-D, mecoprop and dicamba — because it kills dandelions, clover and plantain while leaving the grass alone. Crabgrass needs a different tool: a pre-emergent such as prodiamine or dithiopyr applied in early spring, or quinclorac once it is already up. And anything labelled "weed and grass killer" is non-selective: it kills the lawn as readily as the weeds and belongs on driveways and fence lines, not in the turf.
Two checks come before any purchase. First, read your grass type against the label — St. Augustine and centipede are injured by ordinary 2,4-D products and need ones made for southern lawns. Second, check the forecast: most selective sprays work best between roughly 60°F and 85°F and need a dry window afterwards. Get the category, the grass and the weather right, and the brand matters much less than the marketing suggests.
Our Top Picks
- BEST OVERALL: Ortho WeedClear Lawn Weed Killer
↓ Jump to Review - BEST FOR BROADLEAF WEEDS AND CRABGRASS: Spectracide Weed Stop For Lawns Plus Crabgrass Killer
↓ Jump to Review - BEST VALUE FOR LARGE LAWNS: Southern Ag Amine 2,4-D Weed Killer
↓ Jump to Review - BEST FOR NEW LAWNS AND TOUGH WEEDS: Syngenta Tenacity Herbicide
↓ Jump to Review - BEST PRE-EMERGENT: Quali-Pro Prodiamine 65 WDG
↓ Jump to Review - BEST NON-SELECTIVE SPOT SPRAY: Compare-N-Save Concentrate Grass and Weed Killer
↓ Jump to Review - BEST FOR GRAVEL AND AREAS NOTHING SHOULD GROW: Ortho GroundClear Vegetation Killer
↓ Jump to Review
The Three Kinds of Weed Killer
Every weed killer on the shelf falls into one of three groups, and the front of the bottle does not always make it obvious which. The active ingredients panel does.
Selective post-emergent herbicides kill weeds that are already growing and spare the grass. The classic chemistry is the synthetic auxin family — 2,4-D, MCPP (mecoprop), dicamba and triclopyr — which overwhelms the growth regulation of broadleaf plants so they twist, curl and die over one to three weeks. Grasses metabolise these compounds and survive. Quinclorac adds control of crabgrass and some other grassy weeds; mesotrione (Tenacity) works by a different route and bleaches susceptible weeds white.
Non-selective herbicides kill any green plant they touch. Glyphosate is systemic: it moves down to the roots and kills perennials completely, but takes one to two weeks to show. Glufosinate is faster and mostly contact-acting. Pelargonic acid, diquat and horticultural vinegar are pure contact burn-down products — the top growth browns within hours, the roots of perennial weeds survive, and the weed is back in a few weeks.
Pre-emergent herbicides kill nothing that is already visible. They form a chemical barrier in the top layer of soil that stops seeds from establishing as they germinate. Prodiamine, dithiopyr and pendimethalin are the main lawn options; trifluralin is common in garden-bed products. Timing is everything with these, because once the weed has emerged the barrier is irrelevant.
| Type | Common actives | Kills | Safe on lawn? | Use it for |
|---|---|---|---|---|
| Selective broadleaf | 2,4-D, MCPP, dicamba, triclopyr | Dandelion, clover, plantain, chickweed | Yes, on labelled grasses | Weeds growing in turf |
| Selective grassy-weed | Quinclorac, mesotrione | Crabgrass, nimblewill, some broadleaf | Yes, on labelled grasses | Emerged crabgrass, new lawns |
| Southern lawn selective | Atrazine | Winter annuals, some grassy weeds | St. Augustine, centipede only | Warm-season lawns sensitive to 2,4-D |
| Non-selective systemic | Glyphosate | Everything, roots included | No | Paths, fence lines, lawn renovation |
| Non-selective contact | Glufosinate, diquat, pelargonic acid, vinegar | Top growth only | No | Quick burn-down of annual weeds |
| Pre-emergent | Prodiamine, dithiopyr, pendimethalin | Seeds as they germinate | Yes, but blocks grass seed too | Crabgrass and annual weed prevention |
Our Picks by Job
These are chosen by the job each one does best rather than ranked on a single scale, because the best crabgrass preventer and the best fence-line spray are not competing for the same purchase. Read the label of whichever you buy against your grass type before it goes anywhere near the lawn.
What We Like
- Three-way blend covers the common broadleaf weeds
- Widely available in hose-end, trigger and concentrate
- Amine formulation is less prone to vapour drift than esters
What We Don’t Like
- Does nothing to crabgrass or other grassy weeds
- Not for St. Augustine or centipede lawns
- Ready-to-use formats cost far more per square foot than concentrate
Product Specs
- Type: Selective / Broadleaf Lawn Weed Killer
- Rank in this guide: #1
WeedClear is the current name for the line that was long sold as Ortho Weed B Gon, and it is the straightforward answer for the most common problem: dandelions, clover, plantain and chickweed scattered through a cool-season lawn or a bermuda or zoysia lawn. It uses the classic three-way approach — 2,4-D for the easy broadleaf weeds, with mecoprop and dicamba to reach clover and the tougher perennials that 2,4-D alone handles poorly.
It is sold as a hose-end ready-to-spray bottle, a trigger-spray ready-to-use bottle and a concentrate. The hose-end version is the practical choice for a lawn with weeds everywhere; the trigger bottle suits spot-treating a few dozen dandelions. Like most 2,4-D blends, it is not the product for St. Augustine or centipede lawns — check the grass list on the label before buying.
Spectracide Weed Stop For Lawns Plus Crabgrass Killer
See It on AmazonWhat We Like
- Kills emerged crabgrass as well as broadleaf weeds
- One product instead of two for summer weed control
- Good value in concentrate form
What We Don’t Like
- Mature crabgrass often needs a repeat application
- Not for St. Augustine or centipede lawns
- No pre-emergent effect — new crabgrass keeps germinating
Product Specs
- Type: Selective / Broadleaf + Crabgrass
- Rank in this guide: #2
Adding quinclorac to the 2,4-D and dicamba base is what sets this apart. Quinclorac is one of the few consumer-available actives that kills crabgrass after it has emerged, and it also helps on clover. That makes this the bottle to reach for in early summer, when the crabgrass you failed to prevent has appeared alongside the dandelions.
Quinclorac works best on young crabgrass. Once plants have tillered into large clumps in late summer, expect partial control and a second application, and plan a pre-emergent for next spring instead. It is sold in hose-end and concentrate formats.
What We Like
- Lowest cost per 1,000 sq ft in the category
- Excellent on dandelion, plantain and other easy broadleaf weeds
- Amine salt — lower volatility than ester 2,4-D
What We Don’t Like
- Single active: weak on clover, violets and ground ivy
- Requires a sprayer and careful measuring
- Easy to overdose and injure the grass
Product Specs
- Type: Selective / 2,4-D Concentrate
- Rank in this guide: #3
This is straight 2,4-D amine at farm strength — 46.8% dimethylamine salt — and a pint of it mixes into enough spray for a large lawn several times over. For anyone with a pump sprayer and half an acre or more of dandelion-heavy turf, the cost per treatment is a small fraction of any ready-to-use product.
The trade-off is that 2,4-D on its own is weak on clover, ground ivy, wild violet and spurge, which is precisely why the three-way blends exist. It also asks more of the user: you measure, mix and calibrate yourself, and the label rates must be followed exactly, with reduced rates or exclusions for sensitive grasses.
What We Like
- Safe at seeding on the main cool-season grasses
- Controls nimblewill and other hard-to-kill weeds
- An 8 oz bottle goes a long way at label rates
What We Don’t Like
- Needs surfactant and multiple applications
- Temporary whitening of treated weeds and sometimes the turf
- Not for bermudagrass lawns
Product Specs
- Type: Selective / Mesotrione Pre + Post
- Rank in this guide: #4
Tenacity is a professional turf product (mesotrione) that has become a homeowner favourite for two reasons. It can be applied at seeding on Kentucky bluegrass, perennial ryegrass and tall fescue — something 2,4-D products cannot do — so it controls weeds while a new lawn establishes. And it kills several weeds that conventional sprays struggle with, including nimblewill, young crabgrass and ground ivy, with suppression of creeping bentgrass.
Treated weeds turn bright white before they die, which is alarming the first time and normal. Post-emergent use needs a non-ionic surfactant in the tank, and stubborn weeds usually need two or three applications a few weeks apart. It is labelled mainly for cool-season lawns plus a few warm-season species such as centipede; bermudagrass is injured by it.
What We Like
- Very long residual from one application
- Low cost per acre compared with retail crabgrass preventers
- Stays in place — low leaching
What We Don’t Like
- No effect on weeds already growing
- Prevents overseeding for months
- Must be mixed and sprayed, then watered in
Product Specs
- Type: Pre-Emergent / Crabgrass Preventer
- Rank in this guide: #5
Prodiamine is the same active ingredient as Syngenta's Barricade, and in water-dispersible granule form it is the most economical way to keep crabgrass, goosegrass and many annual broadleaf weeds out of a lawn. It binds tightly to the soil and stays put, giving one of the longest residuals of any pre-emergent — often a full season from one properly timed application, or longer split across two.
It kills nothing that has already germinated and must be watered in to activate. The serious trade-off is that it blocks grass seed as effectively as crabgrass seed, so you cannot overseed treated areas for several months. If you plan to seed in spring, use Tenacity or skip the pre-emergent that year.
Compare-N-Save Concentrate Grass and Weed Killer
See It on AmazonWhat We Like
- Kills roots of perennial weeds and grasses
- No residual — reseed or replant soon after
- Very low cost per gallon of mixed spray
What We Don’t Like
- Kills lawn grass on contact — drift is the main risk
- Slow: one to two weeks to full effect
- Weak on some tough perennials without repeat treatment
Product Specs
- Type: Non-Selective / 41% Glyphosate Concentrate
- Rank in this guide: #6
A plain 41% glyphosate concentrate, which matters more since consumer-branded Roundup changed formula (see below). Glyphosate moves through the plant to the roots, so it kills perennial weeds and grasses outright rather than burning off the top. That makes it the right tool for fence lines, mulched paths, cracks in hardscape and for killing off a patch of lawn — or bermudagrass in a fescue lawn — before reseeding.
Results take one to two weeks to show, which tempts people to re-spray too soon. It has no useful soil residual, so you can usually reseed a treated area within about a week — check the label for the exact interval. It will kill your grass and anything else it lands on, so spot-spray with a coarse nozzle on a still day.
Ortho GroundClear Vegetation Killer
See It on AmazonWhat We Like
- Prevents regrowth for months, not weeks
- Ideal for gravel, edges and hardscape margins
- Fewer repeat applications than contact sprays
What We Don’t Like
- Can injure trees and shrubs through their roots
- Nothing can be planted in treated soil for a long time
- Runoff can kill grass downhill
Product Specs
- Type: Non-Selective / Long-Residual Vegetation Killer
- Rank in this guide: #7
GroundClear Vegetation Killer pairs a knockdown with a soil-active residual and is marketed to prevent regrowth for up to a year. That is exactly what you want on a gravel drive, a patio edge, a utility strip or along a foundation where nothing should ever grow, and it saves spraying the same ground every few weeks.
The residual is also the danger. It moves in soil and runoff and can be taken up by the roots of trees and shrubs that extend well beyond their canopy. Never use it on a lawn, in planting beds, over tree root zones, or on slopes that drain toward anything you want to keep alive.
Which Chemistry Kills Which Weed
Identify the weed before buying. A product that is excellent on dandelions may barely slow ground ivy, and no broadleaf spray will touch crabgrass or nutsedge.
| Weed | What works | Best timing |
|---|---|---|
| Dandelion, plantain | Any 2,4-D product | Fall, or spring before flowering |
| White clover | Dicamba, MCPP, triclopyr, quinclorac | Fall or late spring |
| Ground ivy (creeping Charlie) | Triclopyr, dicamba; mesotrione | Fall, repeat in spring |
| Wild violet | Triclopyr, multiple applications | Fall |
| Crabgrass (prevent) | Prodiamine, dithiopyr, pendimethalin | Before soil reaches 55°F for several days |
| Crabgrass (emerged) | Quinclorac; mesotrione on young plants | Early summer, while small |
| Nutsedge | Halosulfuron or sulfentrazone products | Early summer, before tubers multiply |
| Spurge, chickweed | Three-way blends; pre-emergent for spurge | When young |
| Bermudagrass in a cool-season lawn | No clean selective option — spot glyphosate and reseed | Late summer, ahead of fall seeding |
Fall is the most underrated window for perennial broadleaf weeds. As days shorten, dandelions, clover and ground ivy move sugars down to their roots for winter, and a systemic herbicide applied then travels with them. A September or October application on a cool-season lawn routinely does more than two in spring.
Crabgrass is the opposite case. It is an annual that dies with the first frost and returns from seed, so the effective fight is the pre-emergent in early spring. Dithiopyr has an advantage here over prodiamine: it also kills very young crabgrass seedlings before they tiller, giving some forgiveness if you apply a little late. Prodiamine lasts longer but has no post-emergent effect at all.
Check Your Grass Type First
Selective only means selective for the grasses listed on the label. The same spray that leaves fescue untouched can yellow or kill a sensitive warm-season lawn.
Cool-season grasses — Kentucky bluegrass, perennial ryegrass, tall fescue and fine fescues — tolerate the standard 2,4-D, MCPP and dicamba blends, quinclorac and mesotrione. Fine fescues are somewhat more sensitive to some products; read the label if your lawn is a shade mix.
Bermudagrass and zoysia tolerate most 2,4-D blends when the grass is fully green and actively growing. Avoid spraying during spring green-up, when the turf is most vulnerable, and keep mesotrione off bermuda.
St. Augustine and centipede are where most lawn damage happens. Both are sensitive to 2,4-D, and many standard three-way products either exclude them or require reduced rates. For these lawns the traditional choice is atrazine, which controls many winter annual broadleaf weeds and some grassy weeds and also has pre-emergent activity. Atrazine is only for warm-season lawns — it will damage cool-season grasses — and it is typically restricted from use near water and on sandy soils over shallow groundwater, so the label limits matter. Look for products sold specifically for St. Augustine or southern lawns, and confirm the grass is named on the label.
Newly seeded or sodded lawns should not see 2,4-D-type products until the new grass has been mowed three or four times; labels often specify a waiting period of several weeks. Mesotrione is the main exception for cool-season seedings.
Timing, Temperature and Rain
Most failed weed treatments are timing failures rather than product failures. Selective herbicides work through the plant's own growth, so they need weeds that are actively growing, not dormant, drought-stressed or cooked by heat.
Temperature
The useful range for broadleaf sprays is roughly 60°F to 85°F. Below about 55°F, weeds grow too slowly to move the herbicide and results stall. Above 85–90°F, two problems appear: the turf itself is heat-stressed and more easily injured, and volatile ingredients — dicamba and any ester formulation of 2,4-D — can vaporise and move off-target as a gas. Many labels state an upper temperature limit; treat it as a hard limit. In a hot southern summer, that often means spraying in the cool of early morning, or waiting for fall.
Rain and irrigation
Liquid sprays need to dry on the leaf before rain or sprinklers wash them off. Most consumer liquids state a rainfast period on the label, commonly somewhere between one and several hours; check yours and plan for a dry afternoon. Granular weed-and-feed works the other way: it needs damp leaves for the particles to stick and then roughly 24 hours without rain or watering.
Mowing
Do not mow for a couple of days before or after a broadleaf application. Weeds need leaf area to absorb the spray, and they need time afterwards to move it down to the roots. Mowing high — the single cheapest weed control there is — also shades out weed seedlings; a sharp blade on a good mower set at the right height does more long-term work than any bottle.
Soil temperature for pre-emergents
Crabgrass germinates when soil at about two inches stays near 55°F for several days. A practical marker in much of the country is forsythia blooming. Apply pre-emergent a week or two before that, water in with about half an inch of water, and consider a second, split application six to eight weeks later for season-long control.
Concentrate, Ready-to-Use or Granular
The same chemistry is sold in several packages, and the package changes the cost far more than the brand.
Ready-to-use trigger bottles are pre-diluted and ideal for spot-treating a handful of weeds. They are by far the most expensive way to buy herbicide per square foot, and they make no sense for whole-lawn treatment.
Hose-end ready-to-spray bottles meter concentrate into the water stream from a garden hose. They are fast and convenient for broadcast spraying a moderate lawn, though less precise than a pump sprayer — walking speed and water pressure both change the dose. Typical retail prices sit in the $10–$25 range per bottle.
Concentrates are mixed in a pump or backpack sprayer. They cost the least per treatment, often by a factor of five or more, and give the most control over rate and placement. They also put the measuring on you. Use a dedicated sprayer for herbicides only, labelled, and never use it for anything else — residue of a lawn herbicide in a sprayer later used on vegetables or shrubs is a common source of mysterious plant damage.
Granular weed-and-feed products such as Scotts Turf Builder Weed & Feed combine fertiliser with a broadleaf herbicide spread through a rotary spreader. They are simple, but the compromise is real: the herbicide lands across the entire lawn whether or not there are weeds, the fertiliser timing rarely matches the ideal weed timing, and granules need dew or a light watering to stick to weed leaves. For a lawn with weeds throughout and an owner who will not use a sprayer, they are reasonable. For a lawn with scattered weeds, a spot spray uses a fraction of the chemical.
Driveways, Patios and Paver Joints
Weeds in hardscape are a different problem, because there is no lawn to protect and the real cause is usually the joint or crack itself.
For occasional weeds in cracks, a contact product — pelargonic acid, a glufosinate spray or horticultural vinegar — browns them off within hours. Annual weeds die; perennials regrow from the root and need glyphosate. For gravel and margins that should stay bare all season, a long-residual vegetation killer saves repeat work, with the root-zone cautions above. Boiling water works on small areas of paving and costs nothing.
Killing the weed only treats the symptom. Weeds in paver joints usually mean the joint sand has washed out or never locked. Refilling with a good polymeric sand hardens the joint and leaves almost nowhere for seeds to root; the difference from ordinary joint sand is precisely this. On asphalt, weeds follow cracks, so filling them with an asphalt crack filler after treatment is what keeps them gone. Moss on a shaded drive is its own problem with different fixes — see how to remove moss from an asphalt driveway.
One caution with vinegar: the horticultural strengths sold for weeds, at 20% acetic acid and above, are far stronger than kitchen vinegar and can cause serious eye and skin burns. Wear eye protection and gloves, and keep it away from natural stone and fresh concrete, which acid etches.
Pets, Kids, Drift and Trees
Follow the label. The label is the legal instruction for each product and lists re-entry guidance, protective equipment and restrictions. For most consumer lawn sprays, the guidance is to keep people and pets off treated areas until the spray has completely dried. For granular products, keep them off until the product has been watered in and the grass has dried. Store concentrates in their original containers, locked away from children, and never decant herbicide into drinks bottles.
Spot-treat rather than broadcast wherever possible. Treating only the weeds reduces how much herbicide goes down overall, and where pets and children play, that is a reasonable priority.
Drift is the most common way homeowners damage plants they did not mean to treat. Fine droplets travel a long way in a breeze. Spray when the wind is under about 10 mph and not blowing toward gardens or neighbours, use a coarse-spray nozzle at low pressure, and keep the nozzle close to the target. Tomatoes, grapes and roses are notably sensitive to 2,4-D and dicamba drift — distorted, cupped leaves are the giveaway. Vapour drift from volatile products on hot days can travel even when there is no wind, which is another reason to respect the temperature limits.
Trees and shrubs generally tolerate selective lawn herbicides on the turf beneath them at label rates, but dicamba is root-active and repeated heavy use over root zones can cause injury. Long-residual vegetation killers are the serious hazard: tree roots spread two to three times the width of the canopy, and those products can be absorbed far from the trunk.
Water. Never spray near storm drains, ponds or streams unless the product is labelled for it, and sweep any granules off driveways and paths back onto the lawn — granules left on hardscape wash straight into drains.
Mistakes That Waste the Spray
Using a "weed and grass killer" on the lawn. The single most expensive mistake on this page. If the label says it kills grasses, it kills yours.
Spraying a broadleaf product at crabgrass. 2,4-D, MCPP and dicamba do nothing to crabgrass. Use quinclorac after it emerges, or a pre-emergent before it does.
Applying pre-emergent and then seeding. The barrier stops grass seed as well. Seed and pre-emergent need separating by months, or use mesotrione.
Over-concentrating the mix. More is not better with selective herbicides. Excess rates overwhelm the grass's ability to metabolise the product and injure the lawn, often while killing the weed no faster.
Spraying in heat or drought. Stressed weeds absorb little; stressed grass is easily scorched. Wait for a cooler spell or irrigate a day or two beforehand.
Judging results too early. Systemic products take one to three weeks. Re-spraying after three days doubles the dose for no gain.
Treating weeds without fixing why they are there. Thin turf, compacted soil and mowing too short are invitations. A dense lawn mowed high is the long-term weed control; the herbicide just buys time to get there.
The Short Version
For broadleaf weeds in a cool-season, bermuda or zoysia lawn, buy a three-way selective such as Ortho WeedClear, and apply it in fall for the best results on perennials. If crabgrass is already up, a quinclorac blend handles both at once.
To keep crabgrass out next year, apply prodiamine in early spring before soil reaches 55°F — unless you plan to seed, in which case use Tenacity.
For St. Augustine and centipede lawns, use only products that name those grasses on the label, usually atrazine-based, and respect the heat limits.
Keep glyphosate and long-residual vegetation killers off the lawn entirely: they are for paths, fences, gravel and renovation. And whatever you buy, the label's grass list, temperature limit and rainfast window decide whether it works more than the brand ever will.
Frequently Asked Questions
A selective broadleaf herbicide, which kills dandelions, clover, plantain and similar weeds while sparing labelled lawn grasses. The most effective for general use are three-way blends of 2,4-D, MCPP (mecoprop) and dicamba, such as Ortho WeedClear Lawn Weed Killer, because the three actives together cover far more weed species than 2,4-D alone. If crabgrass is also present, a blend that adds quinclorac, such as Spectracide Weed Stop For Lawns Plus Crabgrass Killer, handles both. The key qualification is grass type: St. Augustine and centipede lawns are injured by ordinary 2,4-D products and need ones labelled specifically for them, usually atrazine-based.
Selective weed killers target certain types of plants — usually broadleaf weeds — and leave lawn grasses unharmed, so they are sprayed directly over the turf. Non-selective products, including glyphosate, glufosinate, diquat, pelargonic acid and vinegar, kill any green plant they contact, grass included. Non-selective products belong on driveways, paths, fence lines and areas being cleared for renovation. The quickest check is the label: anything described as a "weed and grass killer" or "vegetation killer" is non-selective and will kill your lawn.
For perennial broadleaf weeds such as dandelions, clover and ground ivy, fall is the most effective time, because the plants are moving sugars down to their roots and carry the herbicide with them. Late spring, after the weeds are actively growing, is the second window. Spray when air temperatures are roughly 60–85°F, the wind is light, no rain is forecast within the label's rainfast period, and the lawn has not been mowed for a couple of days either side. Crabgrass is different: prevent it with a pre-emergent in early spring, before soil temperature reaches about 55°F for several days.
Above about 85–90°F, usually yes. Heat stresses the lawn so it is more easily injured, drought-stressed weeds absorb little herbicide, and volatile ingredients such as dicamba and ester forms of 2,4-D can vaporise and drift off-target as a gas, damaging garden plants even without wind. Many labels state a maximum temperature; follow it. In hot regions, spray in the early morning when temperatures are lower, or wait until fall, which is the better season for perennial weeds anyway.
Follow the specific product label, which is the legal instruction for that product. For most consumer liquid lawn herbicides, the guidance is to keep people and pets off the treated area until the spray has completely dried — typically a few hours on a warm, dry day. For granular weed-and-feed, keep them off until the product has been watered in and the grass has dried again. Spot-treating individual weeds rather than broadcasting over the whole lawn reduces how much herbicide is applied where children and animals play.
Only products that list St. Augustine on the label. The grass is sensitive to 2,4-D, so many standard broadleaf blends either exclude it or require reduced rates. Atrazine-based products are the traditional choice for St. Augustine and centipede: they control many winter annual broadleaf weeds and some grassy weeds and also have pre-emergent activity. Atrazine is only for warm-season lawns and has restrictions near water and on sandy soils, and it should not be applied during temperature extremes or spring green-up. Always confirm the grass is named on the label and observe its heat limit.
Not in the US consumer lawn-and-garden line. Bayer replaced glyphosate in its residential Roundup products starting in 2023, and current consumer bottles use other actives — depending on the product, combinations such as diquat, fluazifop and triclopyr, with some adding a soil residual. They are still non-selective and will kill lawn grass. Glyphosate remains available in professional and agricultural products and in generic 41% concentrates. Because the formulas differ, read the active ingredients on any bottle rather than assuming it behaves like the old Roundup.
It depends entirely on the product. After 2,4-D-type broadleaf sprays, labels typically require a waiting period of several weeks before seeding. Glyphosate has no useful soil residual, so treated areas can usually be reseeded within about a week, per the label. Pre-emergents such as prodiamine block grass seed for months, which is why you should not use them in a season you plan to overseed. Mesotrione (Tenacity) is the notable exception — it can be applied at seeding on Kentucky bluegrass, perennial ryegrass and tall fescue. Long-residual vegetation killers can prevent anything growing for a year or more.