You pull one strand of greenbrier, and five more shoot back. A standard weed killer (a general-purpose spray that targets only soft-leaf plants) slides right off their waxy leaves. You need a herbicide with triclopyr (a compound that punches through waxy leaves and travels to the roots) to stop them for good. The Crossbow 128oz (Helena) is the best overall buy — it gives you the most triclopyr for your dollar and works in two hours of dry weather — but the right pick depends on the size of your patch and your budget.
I’m Rikta — the co-founder and writer behind Lawn Gear Lab. This guide is built by comparing the manufacturers’ published specifications and the patterns across verified customer reviews, so you get each pick’s real strengths and trade-offs instead of marketing spin.
The key is a herbicide containing triclopyr (a compound that penetrates woody stems and travels to the roots), and we focus on ready-to-mix concentrates that deliver the best bang for your acre. You will find the herbicide for briars that matches your property size and budget.
How To Choose The Best Herbicide For Briars
Not all weed killers are built for woody stems. Here is what separates a briar killer from a general-purpose spray.
Look for Triclopyr as the Active Ingredient
Triclopyr is a selective systemic herbicide (a chemical absorbed by leaves and roots, then carried through the plant) that mimics a natural plant hormone, causing uncontrolled growth that kills the plant from the roots up. It is the standard for blackberry, greenbrier, poison ivy, and hardwood brush, and it leaves most grasses unharmed.
Concentrate vs. Ready-to-Use
Concentrates let you mix your own solution, giving you far more coverage per dollar. A 32-oz bottle typically treats 1,500 square feet when mixed per label directions, while a 2.5-gallon jug can cover 2.5 acres. For any infestation bigger than a garden spot, a concentrate saves money.
Check for Rainfastness
Rainfastness tells you how long the spray needs to dry on the leaf before rain will wash it off. A good choice dries in 30 minutes to 2 hours, so you can apply it without worrying about the afternoon forecast.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| Crossbow 128oz (Helena) | Premium | Large properties & cost-per-ounce savings | 1 Gallon (128 fl oz) | Amazon |
| Crossbow 2.5 Gallon | Premium | Acre-plus infestations | 2.5 Gallons (320 fl oz) | Amazon |
| Roundup Poison Ivy Plus Tough Brush Killer₂ | Mid-Range | Fast results on poison ivy & blackberry | 32 fl oz; 1500 sq ft coverage | Amazon |
| Monterey Brush and Vine Control | Mid-Range | Stump treatment & resprout prevention | 32 fl oz; includes measuring spoon | Amazon |
| Southern AG Brush Weed Killer | Value | Budget buy for small patches | 32 fl oz; 512-1024 sq ft/gal | Amazon |
In‑Depth Reviews
1. Crossbow Herbicide 128oz- Triclopyr + 2,4-D Ester – Helena
128 ounces per jug (four times the concentrate of a standard 32-ounce bottle) makes the Crossbow 128oz from Helena the top pick for anyone clearing fence lines, pastures, or large blackberry thickets who wants to avoid mixing a new batch every trip.
Crossbow is a post-emergent selective herbicide that targets broadleaf weeds and woody plants after they sprout, killing blackberries and poison oak while sparing grass. It is rainfast in 2 hours — spray at 8 a.m., and a noon shower will not wash the chemical off. One long-time buyer calls it their “go to brand for weed control” for the past forty years. The 2,4-D ester helps the triclopyr drive deeper into woody stems. Compared to the Southern AG bottle, Crossbow gives you more than triple the concentrate for roughly 20% more upfront cost.
Skip this one if you only have a small patch of briars and cannot store a gallon jug. For anyone with fence lines or pastures, the Crossbow 128oz is the best balance of price and convenience — it dominates every smaller option on value-per-ounce.
Why it’s great
- Best cost per ounce of any herbicide in this review
- Selective — kills woody brush but spares grass
- Rainfast in just 2 hours for reliable application
Good to know
- Heavier jug (30 lbs for the 2.5-gal version) needs a sturdy sprayer
- Not for edible crops or near water sources
2. Crossbow Herbicide (2.5 Gallon)
Against the top pick’s 1-gallon Crossbow (128 fluid ounces, covering about one acre), this 2.5-gallon jug (320 fluid ounces) covers 2.5 acres of briars per the label instructions — more than double the area for a single purchase. One buyer fighting “thistles, autumn olive, Japanese barberry and broadleaf weeds” says “spraying them once kills the weeds every time,” and another user simply reports, “Kills Blackberries dead.”
The triclopyr active ingredient (a selective systemic herbicide, absorbed by leaves and roots then moved through the plant) is the same chemical used in the Southern AG and Monterey formulas, but at a higher concentration for woody brush. It is selective, so your grass survives. The big trade-off: the jug weighs 30 pounds. If you are hauling it to a backpack sprayer on foot, that is heavy. A tractor-mounted spray rig or a tow-behind tank handles it easily. Stick with the 1-gallon Crossbow if you hand-spray.
Choose this 2.5-gallon size over the top pick only if you manage two-plus acres of overgrown land and have a tractor-mounted spray rig or tow-behind tank to handle the 30-pound jug.
Where it shines
- Covers 2.5 acres — most coverage per purchase
- Same proven triclopyr chemistry as the smaller Crossbow
- Reviewers confirm it kills blackberry and woody brush dead
Worth noting
- Very heavy (30 pounds) — best for spray rigs, not backpack walking
- Restricted in some states; check local laws before buying
3. Roundup Poison Ivy Plus Tough Brush Killer₂ Concentrate
Poison ivy on the fence posts and blackberry brambles in the garden — you want them gone today, not next week. The Roundup concentrate shows visible wilting in hours, not days, and it is rainproof in as fast as 30 minutes. Compare that to the Crossbow’s 2-hour dry window or the Monterey’s 24-hour window, and you see the advantage. One habitat volunteer reports, “Kills plants with leaves; most die with 1 application, tough plants need a few.”
This formula uses three active ingredients: triclopyr, fluazifop-P-butyl (a grass-safe grass killer), and diquat dibromide (a fast contact killer that speeds up leaf burn). It covers 1,500 square feet per 32-ounce bottle — about 2.9 times the coverage per gallon of the Southern AG option, according to label rates. Buyers confirm it “worked on blackberry and other shrubs” that stump general-purpose sprays. You can replant in as little as 1 to 30 days (check the booklet per your target plant).
The Roundup is the right fast-acting choice if your spray window is tight and weather is uncertain. The catch is that tough plants may need a second application. If you prefer one-and-done treatment and have a dry afternoon ahead, the Crossbow 128oz is more economical for large patches. Rainproof in 30 minutes, visible wilting in hours — no other concentrate in this guide closes a spray window that fast.
What stands out
- Visibly wilts leaves in hours
- Rainproof in just 30 minutes
- Triple active ingredients for hard-to-kill brush
The trade-offs
- Some tough plants need a second application
- Non-selective on broadleaf plants — keep away from desirable shrubs
4. Monterey Brush and Vine Control Bundled with Measuring Spoon – 1 Quart
The single number that matters most in this category is 24 hours — that is the rainfast window Monterey requires, the longest of any pick here.
You cut down a blackberry thicket, and a month later it is back. The Monterey 32-ounce concentrate is designed to stop that cycle. Its triclopyr-based formula works two ways: apply it undiluted to freshly cut stumps to prevent resprouting, or spray diluted mix on leaves to kill poison ivy, alder, blackberry, and honeysuckle. One reviewer found it “very effective after a second application on poison ivy.” The included measuring spoon removes guesswork — that is the #1 reason brush killers fail, because people mix too weak. You use a tank or hose-end sprayer around homes and walkways. A big limitation: the label says avoid rain for 24 hours after application, longer than the 2-hour Crossbow or the 30-minute Roundup. That means you need a full day of dry weather. If you spray and a shower hits within 24 hours, you likely waste your work. Choose Monterey if stumps and resprouts are your main headache and you can time a full dry day. For quick leaf-kill on a smaller budget, the Southern AG or Roundup are better bets.
For the price of a single quart, you get a measuring spoon and a stump-stopping concentrate that outlasts cheaper sprays on regrowth — a fair value if you can wait out the rain.
The upsides
- Included measuring spoon ensures correct mix ratio
- Works as both a foliar spray and a stump treatment
- Kills a wide range of woody vines and brush
Keep in mind
- Rain within 24 hours reduces effectiveness
- Second application needed for stubborn poison ivy
5. Southern AG 01113 Brush Weed Killer, 1 Quart (32 oz)
What you actually get at this lower price is 32 ounces of triclopyr, the same selective systemic herbicide that kills woody plants and broadleaf weeds, but without paying for a gallon you do not need. The Southern AG quart treats 256-512 square feet of briars, depending on the plant, per the label’s mix rates of 512–1,024 square feet per gallon. That is enough for a small backyard patch or a fence-line clump. A buyer in Oregon says it “worked on blackberry and other shrubs” after about two weeks for larger shrubs to turn brown.
The low price means you sacrifice speed and convenience. It lacks the triple-action of the Roundup formula and the quick rainfastness of the Crossbow. One reviewer says it did “nothing to the strangler fig.” You get no measuring tool — you need your own measuring cup. The bottle weighs 9.6 ounces, far lighter than the 30-pound Crossbow 2.5-gallon jug, so carrying it to your sprayer is easy.
This is the pick for a single season of small briar patches. If you have only one or two clumps, the Southern AG stops them without burning cash. For anything larger than about 500 square feet of thicket, the Crossbow 128oz gives you far more coverage for a better price per ounce — making this the exact budget buyer it is perfect for.
Why we’d pick it
- Lowest cost entry into triclopyr-based brush control
- Light bottle — easy to carry and mix
- Proven on blackberry and woody shrubs in home settings
A few caveats
- Slower results — larger shrubs take about two weeks
- Smaller coverage area than any other product here
Understanding the Specs
Triclopyr
Triclopyr is a selective systemic herbicide (absorbed by leaves and roots, then moved throughout the plant) that specifically targets woody plants and broadleaf weeds while leaving most grasses alone. It is the standard active ingredient for briars because it penetrates the waxy, tough leaf surfaces that other herbicides slide off.
Concentrate vs. Ready-to-Use
A concentrate must be mixed with water before spraying; a ready-to-use (RTU) bottle comes pre-mixed. Concentrates cost less per ounce of active ingredient and cover more ground — a 32-ounce concentrate of triclopyr typically yields 2 to 3 gallons of spray solution, while an RTU bottle is used at full strength and evaporates fast on big jobs.
Coverage (Square Feet per Gallon)
This spec tells you how many square feet one gallon of mixed spray will treat. For briars, a lower coverage number (like the Southern AG at 512–1,024 sq ft/gal) means a heavier mix is needed because briars have thick foliage. A higher number (like the Roundup at 1,500 sq ft per 32-oz bottle) suggests a lighter spray, but you may need a second pass on dense patches.
Rainfastness
Rainfastness is the time the spray must stay on the leaf without rain washing it off. The Roundup is rainfast in 30 minutes; the Crossbow in 2 hours. The Monterey advises avoiding rain for 24 hours. A shorter rainfast window means you can spray closer to unpredictable weather and still get a kill.
FAQ
Will triclopyr kill grass around my briars?
How long after spraying can I let my animals back in the area?
Can I use these herbicides near a pond or stream?
Final Thoughts: The Verdict
Across the board, the herbicide for briars winner is the Crossbow 128oz (Helena) because it delivers the best value per ounce of triclopyr, covers a full acre of thicket, and is rainfast in just two hours. If you want fast visible results in under an hour, grab the Roundup Poison Ivy Plus Tough Brush Killer₂. And for the budget-conscious person tackling a small backyard patch, the standout is the Southern AG Brush Weed Killer for its light bottle and low entry price.