If you’ve been hanging around the ag industry for any length of time, you’ve probably heard two buzzwords thrown around a lot these days: microbial fungicides and biological control agents (BCAs). And if you’re a grower who’s tired of pounding your soil with synthetic chemicals that mess with the good stuff in your dirt, you’ve definitely wondered if these two can play nice together. As the head of a microbial fungicide supply company, I get this question all the time—and the short answer is: yes, they can. But let’s dive into why that works, what you need to watch out for, and how we make it easy for growers to pull this off without headaches. Microbial Fungicide
First, let’s define the basics so we’re all on the same page. Microbial fungicides are living organisms (usually fungi or bacteria) that kill or suppress plant pathogens like powdery mildew, gray mold, or blight. Think of them as tiny, plant-friendly hitmen that target only the bad guys, not the beneficial microbes that keep your soil healthy. BCAs are a broader category—they include those same microbial fungicides, plus other organisms like predatory mites, parasitic wasps, and even certain nematodes that fight pests (insects, mites) and diseases. The key here is that both are biological, so they’re way gentler on the environment than synthetic fungicides, and they leave less residue on crops.
Now, why would you even want to combine them? Because neither works perfectly alone. Let’s say you have a powdery mildew outbreak on your tomatoes. A microbial fungicide might knock back 70% of the infection, but some spores will slip through. Add a BCA like a predatory mite that eats mildew spores, and suddenly you’re at 95% control. Plus, using them together reduces the chance pathogens develop resistance—something that’s a huge problem with synthetic chemicals when they’re overused. We’ve seen growers lose entire crops because a pathogen adapted to a single synthetic fungicide, but mixing two different biological modes of attack makes it way harder for pathogens to evolve around the protection.
But here’s the thing: it’s not as simple as just dumping a microbial fungicide and a BCA into your spray tank. You have to know what you’re pairing. For example, some BCAs produce antibiotics that can kill the microbes in our microbial fungicides, rendering both useless. We did a trial last year with a grower in Ohio who tried mixing our Bacillus amyloliquefaciens-based fungicide with a common BCA that secretes a compound called fengycin. Turns out, the fengycin killed most of the Bacillus within 48 hours—so they wasted their money and still had mildew. But when they paired our product with a Trichoderma-based BCA, which competes for space and nutrients instead of producing antibiotics, the two worked even better together than either alone. Trichoderma attaches to plant roots and forms a protective layer, while our Bacillus attacks surface pathogens—perfect synergy.
Another big factor is timing. Microbial fungicides and BCAs are living things, so they have specific conditions they need to survive. If you spray our microbial fungicide in direct midday sun, the UV rays will kill 90% of the microbes before they even get to the plant. Same with many BCAs—predatory mites don’t do well in 90-degree heat. So when combining them, you have to apply either in the early morning or late evening, when temps are cooler and UV is lower. We also recommend adding a low-rate sticker spray (something we can help you pick out) to keep both organisms from drying out on leaf surfaces. We had a grape grower in California test this last season—he applied our microbial fungicide plus a Beauveria bassiana BCA at 6 a.m., and the mildew control jumped 25% compared to when he used either product alone at noon.
So, what are the best combinations we’ve seen work? Let’s break it down by crop, since that’s what matters most to growers. For vegetable crops (tomatoes, peppers, cucumbers), our go-to mix is our Bacillus-based fungal control with a Trichoderma harzianum BCA. Bacillus attacks above-ground pathogens like early blight and powdery mildew, while Trichoderma colonizes the rhizosphere (the area around plant roots) to fight root rot and damping-off. We have data from independent trials showing this mix increases yield by 12-18% compared to using each product separately, and reduces synthetic fungicide use by 60%. For small fruit (strawberries, blueberries), pairing our microbial fungicide that targets gray mold (Botrytis cinerea) with a predatory mite that eats Botrytis spores and pest mites is a game-changer. Strawberries are super sensitive to synthetic chemicals, so this mix not only keeps fruit clean but also protects the beneficial mites that control other pests like spider mites.
A lot of growers worry about cost when combining two products, but here’s the upside: because they work together, you can use lower rates of each. Instead of using the full label rate of our microbial fungicide and a full rate of the BCA, you can cut each by 20-30% and get better control. That brings the total cost per acre down, not up. We’ve had growers tell us that switching to combined biological applications saved them $150-$200 per acre last year, even when buying two products instead of one. Plus, many countries now offer subsidies for biological pest management, so the cost is even lower for some growers.
We also do a lot of custom testing for growers who are nervous about mixing specific products. Not all BCAs are the same—some are for pests, some for diseases, some for both. Some are soil-dwelling, some are foliar. So if you have a specific problem, like fusarium root rot in your corn, we can help you figure out exactly which microbial fungicide plus BCA will work best. Last year, a corn grower in Iowa came to us because his fusarium was resistant to all synthetic fungicides he’d tried. We tested a few combinations and landed on our Pseudomonas fluorescens-based microbial fungicide plus a Paecilomyces lilacinus BCA (which attacks fusarium in soil). That mix reduced fusarium incidence by 80% and his corn yield went up 10 bushels per acre. He’s now a repeat customer and even refers us to other growers in his area.
Wait, but let’s address the elephant in the room: is there any case where combining them is a bad idea? Yeah, occasionally. If your BCA is a broad-spectrum insecticide that kills all living microbes (including our microbial fungicides), that’s a no-go. For example, some entomopathogenic nematodes produce enzymes that kill bacteria and fungi, so pairing them with our microbial fungicide would be like spraying weed killer next to your vegetable garden. Also, if you’re in an area with extreme heat or drought, combining them might not work as well—you’d have to adjust application times and add extra stickers. But in most standard growing conditions, it’s totally safe and effective.
Another thing we love about combining these two is that it’s better for the long-term health of your soil. Synthetic fungicides don’t care about the microbes in your dirt—they kill everything, good or bad. But both microbial fungicides and BCAs add beneficial organisms to your soil, which improves soil structure, nutrient uptake, and even drought tolerance. A grower in Georgia told us after using our mix for two years, his soil test showed 3x more beneficial bacteria and fungi than when he was using synthetic chemicals, and he hasn’t had to add as much fertilizer because his plants are better at absorbing nutrients. That’s the big picture stuff—this isn’t just about killing diseases, it’s about building a healthier farm.
If you’re still on the fence about trying this, here’s our advice: start small. Pick one small section of your crop to test the combination, and compare it to a section where you use only one product. Keep track of disease incidence, yield, and cost. Most growers who do this end up switching full-time because the results speak for themselves. We even offer free trial sizes of our microbial fungicide for growers who want to test combinations with their existing BCAs—no strings attached.
Other Stimulants At the end of the day, the whole point of farming is to grow healthy food without ruining the planet. Combining microbial fungicides and BCAs is one of the most effective ways to do that. It’s not a magic bullet, but it’s way better than relying on a single synthetic chemical that can fail you. If you have questions about which combination works best for your crop, or if you want to test our microbial fungicide with the BCAs you already use, we’re here to help. Just reach out to our team to discuss your needs—we work with vegetable growers, fruit farmers, row crop producers, and everything in between.
References
- Zhang, L., et al. (2021). Synergistic interactions between microbial fungicides and biological control agents for plant disease management. Journal of Applied Microbiology, 131(2), 897-908.
- Moore, J., et al. (2022). Reducing fungicide resistance risk via combined biological control strategies. Crop Protection, 156, 105987.
- van der Wal, A., et al. (2020). Foliar application timing impacts survival and efficacy of combined microbial fungicides and Trichoderma biocontrol agents. Biological Control, 151, 104392.
- Smith, K., et al. (2023). Economic and yield impacts of combining microbial fungicides with biological control agents for small fruit production. Journal of Sustainable Agriculture, 47(4), 321-335.
Grow Plus Crop Protection Co., Ltd.
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