Preventing Resistant Pathogens/Pests: What We Growers Can Do

It is understandable to be skeptical about so-called “biologicals”. But in the age of pesticide and herbicide resistance, here is a reason for rethinking this skepticism. 

By Marie Turner, PhD, Creative Director & Head of Science Communications at Impello Biosciences

As growers know, resistant pests, and the associated loss of chemistries to combat them is an expensive and enormous problem. Not long after herbicides were widely introduced in the 1940s, we saw the first resistant weeds; Not long after we first started using antibiotics to cure so many previously lethal infections, bacteria appeared that we could not kill with these tools. By the time I was working on my first agricultural degree, around the turn of the century, pesticide resistance had reached a low rumble; by the time I finished grad school in soil and crops a decade later, the rumble had become a roar.

If you are a grower, you know this harsh reality like the back of your hand. Resistance continues to crop up across all domains of life, from weeds, to insects, to bacteria and fungus, which leaves growers wondering what the future of IPM is; what it means for our day to day operations and budgets. So what are we to do?

What does the evolution of IPM look like?

Of course, we know there are things we can try to do to keep chemistries relevant and pests from becoming resistant nightmares, we are told we should use “biologicals” when possible, rotate crops, rotate chemistries, monitor populations, and avoid indiscriminate killing of non-target organisms. All are standard tenets of IPM. But also, often, the foregone assumption built into IPM is that at some point, an infestation will become such that traditional pesticides or herbicides are the only solutions left. If this is the forgone assumption of IPM, and the forgone conclusion of using these triage chemicals is that they will produce populations with resistance, then where does this leave us over the long haul? What does it mean that the inevitable consequence of using these tools, is that we will, inevitably, eventually, not be able to use them?

What if, I wonder, we made a different assumption? What if our livelihood-supporting crops could be managed in such a way that uncontrollable populations of pests were not a foregone conclusion? What if pests could be managed so that the painful impact on our bottom lines was an exceptional rarity, rather than an ongoing struggle?

Applying pesticides that work by killing organisms is only a (very) short term solution. And, it creates long-term problems. 

Agricultural scientists have modeled the evolution of resistance to both weeds and pathogens and shown that yes, using the aforementioned IPM methods it is possible to at least slow down the evolution of resistance. But the thing consistently shown across all of these simulations, whether bindweed or powdery mildew, kochia or botrytis, is that unless you fully knockdown every last organism, resistance will evolve. What has also been shown (and anyone who grows has to come to terms with) is that a 100% kill is a near-impossibility. 

I want to be clear that merely slapping the name “biological” on a product does not make it exempt from causing resistance. It all comes down to selection pressure, which itself comes down to mode of action. How does a product actually work to create a healthier crop? Does it work by killing things (a very strong selection pressure) or does it work in a different way, by creating a system in which infestation is unlikely?

So, what exactly is a “selection pressure” and why does resistance evolve? Simply put, a “selection pressure” is whatever force determines whether members of a population live or die. So, an herbicide or pesticide that is deliberately designed to kill things is what we call a very strong selection pressure because (at least before resistance began evolving) these things did a pretty darn amazing job of killing most pests in our fields. But, like I said above, unless you are truly able to kill 100% of them, resistance is inevitable. That is, there is no quicker way to create a problematic, resistant pest than to try to wipe it out and (almost) succeed. 

Here is why: As we’ve acknowledged, every time we use a pesticide there will always be a few leftovers– this is a near inevitable truth that every farmer knows. And, if you think about it: Who are these leftovers, who are these holdouts, always going to be? The leftovers are, by definition, going to be those pests or weeds that did the best job of surviving whatever you threw at them. They will be the strongest, most-resistant-to-whatever-you-just-used-to-kill them, pathogens or pests or weeds. Then, these holdouts, these resistant individuals and their genetic abilities will go on to found the entire next generation, in which everyone inherits resistant genetics. And boom. You’ve gone from having something you could kill to something you can’t kill; all in the blink of just a few generations. It’s unfortunate and frustrating, but resistance will always be the consequence of trying to solve a problem by killing it. So then, if we can’t kill things to protect our crops, how might we think about this differently?

Pests and Pathogens always exist. So, how do we create an agricultural system in which they don’t matter?

Enter a preventative approach. You’ve probably heard of preventative medicine, which means that instead of trying to fix patients after they are already ill, doctors try to keep patients from getting sick in the first place by keeping them healthy. For instance, we know if people get good quality sleep, a certain amount of physical exercise, and well-rounded nutrition, they are far more likely not to get major afflictions like cardiopulmonary disease. We know people who consume high levels of vitamin C tend to ward off infections better, and that increased calcium intake results in fewer bone fractures after a fall. At Impello, we don’t think of plants any differently. If you strengthen plant structures with nutrients, like, for example, monosilicic acid, you will make it so crops are less attractive to herbivores, less susceptible to disease, and less subject to breakage and other environmental stressors that are inevitably present in our growing environments. If you create a diverse plant-microbe ecosystem through application of a pre-adapted, co-cultured consortium of microbes, you will make it so there is enough competition in the system that bad pathogens don’t have an opportunity to multiply and become full-fledged disease. 

What is notable about these modes of action is they don’t work by killing anything. They ward off threats by keeping plants and the ecosystems that support them strong. Instead of having to triage and be reactive to a problem once it has already begun (a point at which there have usually already been un-regainable losses to yield and health), these kinds of products create a system in which such problems are not the forgone conclusion. And, crucially, the kinds of indirect, weak selection pressures exerted by health-supporting products won’t result in resistant pests that cause problems for everyone. In the short term and over the long haul, using products that don’t exert strong selection will make the challenging job of productive agriculture easier for all of us.


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