Specs are compiled from manufacturer listings and verified buyer reviews and can change over time — please confirm the key details on the product page before buying.
You walk out to your tomato patch or kale bed and find leaves shredded overnight. That damage is almost always from hungry caterpillars. The most targeted, low-risk fix is a spray made from *Bacillus thuringiensis* (Bt, a naturally occurring soil bacterium that stops leaf-chewing worms without harming your bees, birds, or soil). The challenge is picking the right concentrate or ready-to-use spray from a shelf full of options that all say the same thing.
I’m Rikta — the 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.
You need a bt bacillus thuringiensis spray that matches your garden size, your tolerance for mixing, and the specific pests you are fighting — here is how the top contenders stack up.
Quick Picks
- Bonide 8066 Captain Jack’s Bacillus — Best Overall
- Fertilome (16016) Caterpillar Killer — Top Performer
- Monterey B.t. Bundled with Measuring Spoon – Caterpillar — Most Versatile
- Southern Ag Thuricide BT Caterpillar Control — Budget Champion
- Valent USA Dipel Pro DF Biological Insecticide — Pro Grade
- Monterey B.t. Bundled with Measuring Spoon – Concentrate — Compact Pick
- Southern Ag Thuricide BT For Control of — Bulk Supply
How To Choose The Best BT Bacillus Thuringiensis Spray
Every Bt product on this list works the same way: a caterpillar eats a treated leaf, the bacteria’s protein toxin paralyzes its gut, and it stops feeding within hours. But the differences in concentration, volume, and form matter a lot when you are trying to cover a specific garden size or pest pressure. Here are the three things to get right.
Concentrate vs. Ready-to-Use
A ready-to-use spray comes in a trigger bottle — you pull and spray. It is perfect for small gardens or quick spot-treatments because there is no mixing, no measuring, and no leftover concentrate to store. A concentrate (liquid or powder) saves money per gallon when you have many plants. You mix a small amount of the product with water in a tank sprayer. The trade-off is that you need to mix only what you can use that day because Bt breaks down in sunlight.
Volume and Coverage
A 32-ounce ready-to-use bottle covers a small vegetable patch or a few tomato plants. A pint of concentrate makes many gallons of finished spray — enough for an orchard or a large vegetable garden. The 1-gallon jug of Southern Ag concentrate, for instance, uses just 1 to 4 ounces per gallon of water, so one jug lasts multiple seasons for most home gardeners.
Target Pest and Plant Type
Bt is selective: it only kills caterpillars (the larvae of moths and butterflies). It will not help with aphids, mites, or beetles. All the products here list the same common pests — tomato hornworm, cabbage looper, cabbage worm, tent caterpillar, bagworm, gypsy moth. Check the label to confirm your specific pest and plant — most cover vegetables, shade trees, ornamentals, and fruit.
Quick Comparison
| Model | Best For | Volume | Form | OMRI Listed | Amazon |
|---|---|---|---|---|---|
| Bonide Captain Jack’s 32 oz | Spot-treating small gardens | 32 oz | Ready-to-Use | Yes | Amazon |
| Fertilome Caterpillar Killer 32 oz | Organic vegetable patches | 32 oz | Ready-to-Use | Yes | Amazon |
| Monterey B.t. Concentrate 32 oz | Large gardens & sprayer users | 32 oz | Concentrate | Yes | Amazon |
| Southern Ag Thuricide 16 oz | Budget-friendly concentrate | 16 oz | Concentrate | Yes | Amazon |
| Monterey B.t. Concentrate 16 oz | First-time concentrate buyers | 16 oz | Concentrate | Yes | Amazon |
| Valent USA Dipel Pro DF 1lb | Fast-acting powder option | 1 lb | Powder | Yes | Amazon |
| Southern Ag Thuricide 1 Gal | Season-long bulk supply | 1 Gal | Concentrate | — | Amazon |
In‑Depth Reviews
1. Bonide 8066 Captain Jack’s Bacillus Thuringiensis BT Organic Worm & Caterpillar Control, 32 oz. Ready-to-Use
The ready-to-use trigger sprayer that stops hornworms on sight without any mixing.
This 32-ounce bottle is the easiest way to get started with Bt. You pull the trigger, spray directly onto the leaves where you see caterpillars, and the bacteria gets to work by ingestion (the bugs stop feeding immediately and die within 2 to 3 days). Buyers report that it “killed green caterpillars on basil overnight” and that the plant recovered and looked great after two weeks. The sprayer delivers a fine mist, which owners mention is perfect for coating the undersides of leaves where caterpillars hide.
It is OMRI (Organic Materials Review Institute, which certifies products for organic farms) listed for organic gardening, and the active ingredient is a strain of the bacterium *Bacillus thuringiensis* used worldwide. Unlike the Monterey 32 oz concentrate below, this one weighs 2.33 pounds fully loaded and covers a small to medium vegetable patch without any measuring. It does not have the staying power of a concentrate against heavy infestations, but for quick, precise strikes on tomato hornworms or cabbage loopers, it is tough to top.
The label lists targets like cabbage looper, hornworms, and tent caterpillars for use on broccoli, cauliflower, kale, tomatoes, melons, and more. Because it is a 32-fluid-ounce ready-to-use formula, it costs more per gallon than a concentrate, but the convenience trade-off is real — you will reach for this bottle more often than a measuring cup.
What stands out
- No mixing, measuring, or cleanup required — spray and go
- Fine mist trigger coats leaves evenly, even on undersides
- Safe for bees, earthworms, and birds when used as directed
- Overnight results on small caterpillars, per verified buyers
The trade-off
- Less economical than a concentrate if you have a large garden
- Must reapply after rain, like all Bt sprays
Reach for it when: You have a small-to-medium vegetable patch and want instant spot-treatment without mixing anything.
Look elsewhere if: You need to spray a large orchard or many beds — a concentrate will save you money per treatment.
2. Fertilome (16016) Caterpillar Killer with Bt Biological Insecticide, RTU, OMRI Listed (32 oz.)
The OMRI-listed ready-to-use spray that stopped boxwood moths and broccoli worms fast.
Like the Bonide above, this is a ready-to-use 32-ounce spray — no mixing needed — but it comes from the ferti-lome brand, which has a long track record in garden chemicals. Customers note that two days of applying it eliminated caterpillars on broccoli and that they “didn’t see anymore worms or eaten leaves until the very end of fall.” One reviewer used it successfully against boxwood moths, a tough pest that can defoliate shrubs in a very short amount of time.
This spray is designed to target leaf-chewing worms like tomato hornworm, cabbage looper, tent caterpillar, bagworms, and gypsy moth while leaving non-leaf-eating insects unharmed. It is also OMRI listed, meaning it meets the standards for certified organic production. At 32 fluid ounces and weighing the same as the Bonide, the two are functionally identical in size and form, but buyers call out the Fertilome as especially good for vegetables like broccoli and squash because you can inject it directly into the vine for squash borers.
One catch mentioned by a reviewer: the spray may not have a long residual life in the sun, so plan to reapply after rain or heavy dew. The label says it is non-toxic to humans and pets, but you still want to apply it in the evening when bees are less active.
Why it wins
- Ready-to-use simplicity — no mixing, no measuring
- Selective targeting spares bees and earthworms
- Reviewed buyers saw results in two days on broccoli and boxwood moth
- OMRI listed for organic gardening
Its limit
- Not as cost-effective per gallon as a concentrate for large gardens
- Needs thorough leaf coverage and reapplication after rain
Grab this when: You want a zero-fuss organic solution for common vegetable pests like cabbage worms and hornworms — especially on broccoli or squash.
Skip it when: You need to cover an acre of ornamentals or trees; a concentrate will go further for the same money.
3. Monterey B.t. Bundled with Measuring Spoon – Caterpillar & Worm Killer – 32 oz Concentrate
The concentrate that turns 32 ounces into many gallons of caterpillar-killing spray.
Monterey’s 32-ounce bottle gives you far more finished spray than the ready-to-use options above because it is a concentrate — you mix a small amount with water in a sprayer. The included measuring spoon takes the guesswork out of mixing. Reviewers point out that “Bt only works against caterpillars and not other beneficial insects,” so you can spray knowing your bees and ladybugs are safe. One reviewer noted finding several caterpillars dead on their tomatoes just two days after application.
This product is OMRI listed and designed for use on plants like broccoli, cabbage, cauliflower, melons, lettuce, tomatoes, shade trees, and ornamentals. The active ingredient kills pests by ingestion: the caterpillar eats a treated leaf, stops feeding immediately, and dies within a few days. Because you mix only what you need, there is no waste — one buyer mentioned that “it doesn’t take much” and that it is worth it when you see the results. The 32-fluid-ounce size gives you more concentrate for the price than the 16-ounce Monterey bottle, making it the better value for anyone with a medium to large garden.
The catch is the same as with any Bt: it breaks down in sunlight, so apply in the evening. Buyers also share that they mix only what they can use in one night for the best results.
The strong points
- Concentrate makes many gallons — far more economical than ready-to-use sprays
- Comes with a measuring spoon for precise mixing
- Safe for honeybees, ladybugs, and earthworms when used as directed
- OMRI listed for organic gardening
What to watch
- Requires a sprayer and must be mixed fresh for each application
- Bt degrades in sunlight, so evening spraying is a must
Best for: Gardeners who want the lowest cost per gallon for treating medium-to-large vegetable beds or fruit trees with a tank sprayer.
Not for: Anyone who wants to skip the mixing step — grab a ready-to-use bottle instead.
4. Southern Ag Thuricide BT Caterpillar Control, 16oz – Pint
The pint-sized concentrate that saved collards overnight with its fast-acting caterpillar control.
This 16-ounce pint of Southern Ag Thuricide is a concentrate, not a ready-to-use spray, so you mix it with water in a tank sprayer at a rate the label specifies. At 9.9 ounces, the bottle itself is noticeably lighter than the Fertilome (16016) Caterpillar Killer, which holds 32 fluid ounces, but the Southern Ag makes up for it by stretching far further per ounce. One owner reported, “My collards were beautiful” — after spraying overnight, the caterpillars stopped eating and the damage was gone.
The active ingredient is *Bacillus thuringiensis* subsp. *kurstaki* strain SA-12, a specific strain toxic to listed caterpillars. It is OMRI listed and safe to use on all plants, vegetables, and edible crops with very low toxicity to humans and pets. Shoppers say that it works quickly for bud worms on petunias and Japanese beetle larvae in the lawn, though it is slower-acting than chemical alternatives. At 16 fluid ounces, it is half the volume of the Fertilome product, but because it is a concentrate, you actually get more finished spray from this pint than from a full ready-to-use bottle.
The main downside is the same as the Monterey concentrate: you must mix it yourself and apply it in the evening. One reviewer also noted that it must be ingested by the pest to work, so thorough spray coverage is essential.
Why it stands out
- Concentrate gives you many gallons of spray from a small bottle
- OMRI listed; safe for use on all vegetables and edibles
- Buyers report overnight results on collards and petunias
- Very low toxicity to humans and pets
The catch
- Requires mixing with water and a separate sprayer
- Smaller 16 oz bottle means you will need to buy more sooner than a larger concentrate
Grab this for: A small-to-medium garden where you want to stretch a few dollars into many treatments by mixing your own spray.
Pass on it if: You prefer the grab-and-go convenience of a ready-to-use trigger sprayer.
5. Valent USA Dipel Pro DF Biological Insecticide BT 54%, 1lb Bag
The dry-flowable powder that packs 54% Bt and has no time-to-harvest restrictions.
This is not a liquid concentrate. Dipel Pro DF is a dry-flowable (powder) formulation that you mix with water, containing 54% active *Bacillus thuringiensis* — a much higher concentration than the liquid concentrates above. A 1-pound bag goes a long way. Valent USA is the manufacturer, and the product is OMRI listed. The biggest advantage of a dry formulation over liquids is shelf life: it stores longer without degrading, and you cannot spill it. It also has no time-to-harvest restrictions, meaning you can spray right up to the day you pick your vegetables.
Buyers call it fast-acting, with some reporting that it works quickly after application. Because it is a powder, you must mix it thoroughly with water and keep the suspension agitated in your sprayer to prevent settling. The trade-off for the power and shelf life is that it takes a bit more effort to mix than a liquid concentrate — unlike the Monterey 32 oz concentrate that pours and stirs easily, you need to pre-slurry or shake vigorously. Still, for large gardens or serious organic growers, the cost per gallon is very low.
Note: this product has fewer customer reviews in the data than the liquid options, so feedback is more limited. But its 54% concentration is class-leading among the picks here, making it a choice for experienced gardeners who want maximum potency per ounce.
What makes it different
- 54% Bt concentration is the highest on this list — you use very little per gallon
- Dry powder stores much longer than liquid concentrates
- No pre-harvest waiting period; spray until the day you pick
- OMRI listed for organic production
Keep in mind
- Requires thorough mixing and agitation in the sprayer tank
- Fewer buyer reviews available to gauge real-world consistency
Pick this if: You are an experienced organic grower who wants the highest Bt concentration per dollar and long powder shelf life.
skip it if: You want the simplicity of a liquid concentrate or ready-to-use spray — measuring and mixing powder takes more effort.
6. Monterey B.t. Bundled with Measuring Spoon – Concentrate for BT Spray – 16 oz
The smaller 16-ounce concentrate for gardeners who want the measuring spoon included.
This is essentially the same Monterey concentrate as the 32-ounce version above, but in a 16-ounce bottle with the same included measuring spoon. The active ingredient is identical: it kills cabbage looper, bagworm, gypsy moth, fall cankerworm, and elm spanworm by ingestion. The difference is simply volume — this bottle is half the size, which can be a good thing if you have a small garden and do not want a large bottle of concentrate sitting around for years. The Monterey label states that the product is OMRI listed and safe for earthworms and honeybees when used as directed.
One trade-off compared to the larger Monterey bottle: at 16 ounces, it holds half the concentrate of the 32-ounce version. If the included measuring spoon makes the difference for you (easier mixing than guessing), this is a clean choice.
Why it works
- Compact 16-ounce size won’t crowd your garden shed
- Comes with a measuring spoon for easy, accurate mixing
- OMRI listed and safe for bees and other beneficials
Where it falls short
- Half the volume of the 32-ounce Monterey — worse value per ounce for large gardens
- Still requires a separate sprayer and evening application
Reach for it when: You have a small garden and like the idea of a measuring spoon coming with the bottle so you do not have to guess the mix ratio.
Look elsewhere if: You want the lowest cost per ounce — the 32-ounce Monterey is a better deal for the same product.
7. Southern Ag Thuricide BT For Control of Caterpillars & Worms, 1 Gallon – 128oz
The gallon jug that growers buy once and use for several seasons against every caterpillar pest.
This is the biggest bottle on the list — a full 1-gallon (128 fluid ounces) of Southern Ag Thuricide concentrate. The label says to use just 1 to 4 ounces per gallon of water, so this jug makes many dozens of gallons of finished spray. Owners mention that a single application eliminated tomato worms, squash borers, and cabbage worms, and they love that it is “100% natural and has ZERO effect on humans.” One customer observed that the jug will “probably outlast me” because you only need about 3 teaspoons per gallon of water. Another confirmed that dead bagworms appeared under their tree the morning after spraying.
If you have a large vegetable garden, fruit trees, or ornamentals that face heavy caterpillar pressure each year, this is the most economical way to buy Bt on a per-gallon basis. The trade-off is that 1 gallon of concentrate is a lot of liquid to store, and because Bt breaks down over time, you will need to use it within a couple of seasons. Also, unlike the OMRI-listed products above, this specific label does not appear to carry the OMRI logo in the provided data — though it is still a conventional Bt concentrate safe for organic use.
The big wins
- Huge 1-gallon concentrate makes countless gallons of finished spray
- Customers note one application wiped out caterpillars on trees and vegetables
- Extremely low cost per treatment compared to smaller bottles
The big trade-off
- Large jug requires dedicated storage space and may degrade before you finish it
- No OMRI listed logo in the data (though it is a standard Bt concentrate)
- Must still mix and apply with a sprayer; no ready-to-use convenience
Buy this when: You have a large garden, orchard, or multiple beds and want the absolute lowest cost per spray treatment over the long haul.
Skip it when: You only have a few tomato plants — you will struggle to use all the concentrate before it loses potency.
Understanding the Specs
Ready-to-Use vs. Concentrate
A ready-to-use spray comes pre-mixed in a trigger bottle. You pull the trigger and spray directly on the leaves — no measuring, no mixing, no cleanup. It is ideal for small gardens and quick spot-treatments. A concentrate (liquid or powder) must be mixed with water in a tank sprayer before each use. It costs less per finished gallon, but requires a bit more time and equipment. If you have more than a few tomato plants, a concentrate is the smarter investment.
OMRI Listing
OMRI (the Organic Materials Review Institute) reviews products to ensure they comply with the USDA’s National Organic Program (NOP). An OMRI-listed product can be used in certified organic production. Most of the picks here carry that label, which gives you confidence that the spray will not introduce synthetic chemicals into your soil or harvest. If you are growing strictly organic, look for the OMRI logo on the bottle.
How Bt Works
*Bacillus thuringiensis* is a naturally occurring soil bacterium. When a caterpillar eats a leaf coated with Bt, the bacteria’s protein toxin binds to the insect’s gut, paralyzing it. The caterpillar stops feeding within hours and dies within 2-3 days. Bt is selective: it only affects caterpillars (larvae of moths and butterflies). It does not harm honeybees, ladybugs, earthworms, birds, or people. Because it must be ingested, you need to spray thoroughly so the pest eats the treated leaf.
Application Timing
Bt is a living organism that breaks down quickly in sunlight (UV radiation kills the bacteria). For best results, apply in the late evening or on a cloudy day so the spray has several hours to dry and stay active on the leaves overnight. You also need to reapply after heavy rain, which washes the bacteria off the foliage. Most products recommend spraying when pests first appear, then repeating every 5-7 days until the infestation is under control.
FAQ
Is BT spray safe for bees and ladybugs?
How long does it take BT to kill caterpillars?
Do I need to mix BT with water or can I use it straight?
How long does a bottle of BT spray last on the shelf?
Can I use BT spray on edible plants like tomatoes and broccoli?
Will BT spray kill tomato hornworms?
What is the difference between Thuricide and other BT sprays?
How often should I reapply BT spray?
Will BT spray kill squash vine borers?
What is the best BT spray for a large garden or orchard?
Final Thoughts: The Verdict
For most home gardeners, the bt bacillus thuringiensis spray winner is the Bonide Captain Jack’s 32 oz Ready-to-Use because it combines zero-fuss convenience with overnight results on common pests like hornworms and cabbage loopers. If you want the best value per gallon for a medium-to-large vegetable patch, grab the Monterey B.t. 32 oz Concentrate with spoon. And for those growing an orchard or a massive garden where you need season-long coverage at the lowest cost, the standout is the Southern Ag Thuricide 1-Gallon Concentrate.
How We Picked
We do not accept paid placement. Every pick is matched to a real buyer and a real use-case; we do not hands-on test units.
Sources & Methodology
Specifications: manufacturer listings and product documentation. Review insights: verified customer reviews, as of July 2026. Pricing: not shown on this page (it changes often); check the current price via the retailer link.
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