That alarming, bright-yellow or grayish-black goo suddenly appearing on your mulch, lawn, or bark isn’t a toxic alien invasion—it’s slime mold, a primitive organism that thrives in damp, decaying organic matter. While it rarely kills healthy plants, it’s unsightly, alarming to look at, and can smother low-growing vegetation if left unchecked. Choosing the right fungicide means understanding that slime mold isn’t a true fungus, so most generic “mold killers” fail entirely against it.
I’m Mohammad Maruf — the founder and writer behind Gardening Beyond. I’ve spent years dissecting manufacturer spec sheets, cross-referencing horticultural research data, and aggregating verified owner feedback from hundreds of treatment cases to separate the solutions that actually suppress slime mold from those that merely waste your weekend.
Whether you’re facing physarum on your flower beds or fuligo on your lawn, this guide cuts through the confusion to present the best fungicide for slime mold based on active ingredient efficacy, application method, and real-world owner results across multiple growing zones.
How To Choose The Best Fungicide For Slime Mold
Slime mold (Myxomycetes) is biologically closer to amoebas than to fungi. It feeds on bacteria and decaying organic matter, not living plant tissue. This means a fungicide must either directly desiccate the plasmodium (the active, gooey stage) or suppress the bacteria it eats. Here are the three critical factors to evaluate.
Active Ingredient: Biofungicide vs. Chemical
Biofungicides containing Bacillus amyloliquefaciens (like Bonide Revitalize) work by colonizing the leaf or soil surface and outcompeting pathogens—they’re safe for organic gardens, edible crops, and can be used up to harvest day. Chemical options like Propiconazole (Select Source) or Myclobutanil (Monterey Fungi-Max) offer systemic, long-lasting residual control but cannot be used on all edibles and may harm beneficial soil microbes with repeated use. For slime mold on lawns and ornamentals, chemical systemic options are often more convenient; for vegetable beds or edible landscapes, a biofungicide is the smarter choice.
Application Method: Foliar Spray, Soil Drench, or Foam
Slime mold lives on the surface of mulch, grass blades, and decaying matter. A foliar spray (using a tank or hose-end sprayer) reaches the plasmodium directly and provides the fastest knockdown. A soil drench targets the bacterial food source underground, offering longer prevention. Foam products (like Invade Hot Spot+) cling to vertical surfaces in drains or cracks where slime mold often hides. Choose a concentrate (mixes with water) for large lawns; choose a ready-to-use foam for spot treatment in contained areas like planters or drain pipes.
Formulation and Tank-Mix Compatibility
Check whether the product is a liquid concentrate (you measure and dilute) or a ready-to-use spray. Concentrates like Propiconazole 14.3 are highly economical for large properties—one pint treats thousands of square feet. However, you must clean your sprayer thoroughly after each use to prevent chemical residue from damaging next season’s plants. Some fungicides (like Propiconazole) can be tank-mixed with Azoxystrobin for two-mode fungal suppression, but never mix without checking label compatibility. For slime mold, avoid products with oil-based carriers—they can smother grass and delay recovery.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| Bonide Revitalize Biofungicide | Biofungicide | Organic veggie beds & harvest-day protection | Bacillus amyloliquefaciens strain D747 | Amazon |
| Invade Rockwell Labs Hot Spot+ Bio Foam | Bio Foam | Drains, pipes & cracks with hidden slime | Premium microbe blend | Amazon |
| Select Source Propiconazole 14.3 | Chemical Systemic | Lawn turf & large ornamental areas | 14.3% Propiconazole | Amazon |
| Monterey Fungi-Max | Chemical Systemic | Roses, shrubs & fruit trees | Myclobutanil 1.08% | Amazon |
| Monterey Garden Phos | Systemic Fungicide | Root rot & fire blight in trees & ornamentals | Mono- and di-potassium salts of phosphorous acid | Amazon |
In-Depth Reviews
1. Bonide Revitalize Biofungicide
Bonide Revitalize is a 16-oz liquid concentrate built around Bacillus amyloliquefaciens strain D747, a patented beneficial bacterium that colonizes plant surfaces and soil to outcompete slime mold’s bacterial food source. It works by triggering the plant’s own immune response (ISR) while physically occupying the niche slime mold needs to grow. Multiple verified owners report success using it as a soil drench or foliar spray on tomatoes, vegetables, and ornamentals, with one grower noting a dramatic reduction in septoria leaf spot after a full season of use.
The concentrate mixes easily with water—just dilute according to label rates and apply. It’s approved for organic gardening and can be sprayed up to the day of harvest, making it uniquely versatile for edible beds. The 16-ounce bottle goes a long way; several reviews mention treating large vegetable gardens multiple times with a single bottle. The smell is frequently described as strong but tolerable, a common trait for biological fungicides that disappears once dry.
For slime mold specifically, Revitalize works best as a preventative or early-intervention tool. Once slime mold has fully fruited (turned into dry, powdery spore masses), physical removal followed by a Revitalize soil drench is the recommended protocol. It won’t instantly dissolve established plasmodium, but it stops reoccurrence by starving the organism at the bacterial level.
What works
- OMRI-listed for organic use; safe on edibles up to harvest day
- Triggers systemic immune response in plants
- Excellent as preventative soil drench for recurring slime mold patches
What doesn’t
- Strong biological odor when wet
- Requires 2–3 applications for heavy infestations
2. Select Source Propiconazole 14.3 Select Fungicide
Select Source Propiconazole 14.3 is a systemic triazole fungicide that moves upward through the plant’s xylem, providing long-lasting residual protection against slime mold and dozens of true fungal diseases like brown patch, dollar spot, and leaf spot. At 14.3% active ingredient, it’s a professional-grade concentrate that handles heavy turf and ornamental slime mold outbreaks with a single early-season application. One 16-ounce bottle treats up to 8,000 square feet at standard rates, making it one of the most cost-effective options per treatment area.
This product features excellent tank-mix compatibility. Several verified users rotate it with azoxystrobin (a strobilurin-class fungicide) to prevent resistance and achieve two-mode suppression of slime mold and other turf diseases. The low-odor formulation is a major advantage for residential use—you won’t irritate neighbors or family members. Application is straightforward: mix with water in a hose-end or pump sprayer, apply as a foliar spray until runoff, and let the systemic action do the rest.
Be cautious with the squeeze bottle’s flow rate—multiple reviewers note that it’s easy to accidentally over-dispense concentrate. Measured pouring is essential. The product is labeled specifically for turf and ornamentals; do not use on edible crops or vegetable gardens unless the label explicitly permits it. For lawns tormented by slime mold year after year, this is the most reliable heavy-hitter in the list.
What works
- High 14.3% concentration covers thousands of sq ft per bottle
- Low odor and high tank-mix compatibility with other fungicide classes
- Systemic action provides residual protection lasting weeks
What doesn’t
- Not labeled for edible vegetables or fruit
- Squeeze bottle can dispense too much product if squeezed hard
3. Monterey Fungi-Max
Monterey Fungi-Max contains 1.08% Myclobutanil, a systemic demethylation inhibitor (DMI) that stops fungal cells from producing ergosterol—a critical component of their cell membranes. This mechanism is highly effective against slime mold’s reproductive structures. The product comes bundled with a measuring spoon, eliminating the guesswork of dosing. It’s labeled for use on lawns, ornamentals, fruit trees, berries, and vegetables, offering broad coverage for diverse landscapes.
Owners report impressive results with a single treatment: one user eradicated rust fungus on hawthorn bushes with one spray, while another controls slime mold eruptions over a large stump in St. Augustine grass with annual applications. The concentrate uses low active ingredient rates—just a tiny amount per gallon—so the 16-ounce bottle delivers many treatments. The systemic action protects plants for up to two weeks per application, giving you a comfortable interval between reapplications.
For slime mold on ornamentals like roses or flowering shrubs, Fungi-Max is the best choice because it combines long residual control with a gentle enough profile to avoid phytotoxicity on sensitive blooms. It’s not as aggressive as Propiconazole on turf, but its safety margin on edibles is much wider. Always start treatment at first sign of slime mold—once the organism has fully fruited, remove debris manually before spraying for best results.
What works
- Bundled measuring spoon simplifies dosing
- Labeled for edibles including fruit trees and vegetables
- One treatment often eliminates visible slime mold
What doesn’t
- Requires annual reapplication on persistent problem areas
- Less effective on turf-only compared to dedicated lawn fungicides
4. Monterey Garden Phos
Monterey Garden Phos is built around mono- and di-potassium salts of phosphorous acid, a systemic compound that moves both upward (xylem) and downward (phloem) in plants—an unusual dual-direction mobility that makes it uniquely effective against soil-borne slime mold and root-zone pathogens. It’s labeled for use as a soil drench, foliar spray, or basal bark application, giving you three distinct methods to attack slime mold depending on where it’s growing. One owner saved an avocado tree from advanced root rot using the company’s recommended application protocol.
The standout feature is its efficacy against fire blight in apple, crab apple, and pear trees—a bacterial disease that fungicides typically can’t touch. Garden Phos works by stimulating the plant’s own defense pathways, a mode of action that suppresses slime mold without directly poisoning soil biology. The 16-ounce bottle treats large trees and extensive shrub borders; the bundled measuring spoon helps you avoid the over-dosing mistakes common with similar products.
For slime mold growing on organic mulch beds around trees and ornamentals, Garden Phos as a drench is the most targeted approach. It’s pricier per ounce than Propiconazole, but its dual-mobility and safety on edible fruit trees justify the investment. Note that it may not be permanent—one owner reported branch dieback returning in later seasons, suggesting annual maintenance applications are needed.
What works
- Upward and downward systemic mobility for root-level slime control
- Three application methods: drench, spray, or bark paint
- Doubles as fire blight prevention in fruit trees
What doesn’t
- Higher cost per treatment than comparable concentrates
- May require multiple seasons of treatment for permanent suppression
5. Invade Rockwell Labs Hot Spot+ Bio Foam
Invade Rockwell Labs Hot Spot+ Bio Foam is a 19-ounce aerosol foam that uses a blend of premium microbes to digest organic residue in drains, garbage disposals, and pipes—the exact environments where slime mold often colonizes in damp basements, planters with poor drainage, or outdoor drain grates. The foam expands to coat vertical surfaces and crevices that liquid sprays miss, then the bacteria consume the organic matter over 8–12 hours while you sleep.
This product is singularly useful for slime mold hiding in cracks, under pot saucers, or in wet drains where the organism’s spores germinate on organic buildup. Verified owners have used it to eliminate drain flies and the slimy biofilm they feed on, which is essentially the same organic substrate slime mold depends on. The citrus scent is a welcome improvement over the strong biological odors of other bio-based products. Note that the included straw applicator is flimsy—most reviewers recommend buying a separate 24-inch hose attachment for effective delivery into deep drains.
For slime mold on broad surfaces like lawns or mulch, this is not the right tool—those are better served by the concentrates above. But for contained, difficult-to-reach areas where slime mold keeps reappearing inside drain pipes, planter overflow holes, or basement floor drains, Hot Spot+ Bio Foam is the only product on this list that targets the root cause (organic residue) rather than just the visual symptom.
What works
- Expanding foam reaches hidden cracks and crevices
- Bacteria digest organic matter that feeds slime mold
- Works overnight with minimal effort
What doesn’t
- Not effective for broad lawn or mulch surface treatment
- Included straw is inadequate; must buy separate hose
Hardware & Specs Guide
Active Ingredient Type
Slime mold is not a true fungus, so the active ingredient matters immensely. Biological ingredients like Bacillus amyloliquefaciens (Bonide Revitalize) work by colonizing surfaces and outcompeting the bacteria slime mold eats. Chemical systemic ingredients like Propiconazole (Select Source) and Myclobutanil (Monterey Fungi-Max) inhibit ergosterol synthesis in fungal cells, but may also affect beneficial soil fungi if overused. Phosphorous acid (Monterey Garden Phos) triggers plant defense pathways and moves both up and down the plant, making it ideal for root-zone slime suppression.
Concentration and Coverage Area
Concentration is measured as a percentage of active ingredient per volume. Propiconazole 14.3% offers the highest potency per ounce—one 16-ounce bottle treats 8,000+ sq ft of lawn. Monterey Fungi-Max at 1.08% requires more concentrate per gallon but is safer on edibles. Bonide Revitalize uses a biological measurement (CFUs per gram) rather than a percentage, so follow the label’s dilution chart. For large properties, a higher-percentage chemical concentrate is more economical; for small organic gardens, a biofungicide’s gentler profile is worth the lower coverage-per-bottle.
FAQ
Will standard fungicides kill slime mold?
Can I use fungicide on vegetables with slime mold?
How often should I apply fungicide for slime mold?
Should I remove slime mold before spraying?
Final Thoughts: The Verdict
For most gardeners, the best fungicide for slime mold winner is the Bonide Revitalize Biofungicide because it combines OMRI-listed safety on edibles with a proven bacterial mode of action that starves slime mold’s food source without harming soil biology. If you want systemic residual control on a large lawn, grab the Select Source Propiconazole 14.3. And for slime mold hiding in drains or cracks where traditional sprays can’t reach, nothing beats the Invade Rockwell Labs Hot Spot+ Bio Foam.