If you recognize the utility of sawing off the top foot and a half of a garden hoe shaft, there’s a high likelihood you were the child of a sugarbeet grower prior to 2008 and the introduction of glyphosate resistance into this crop. I count myself among this group of beet-hoeing children and doubt if there is anyone more grateful for the miracle of modern crop protection.
Modern pesticides have enabled the efficiency of current agricultural systems and drastically increased yields worldwide. Pesticide utilization has resulted in a massive reduction in the labor force. Many devastating crop diseases and insect pests can be entirely mitigated by a properly timed foliar fungicide or insecticidal seed treatment. Not only are these pesticides efficacious, but they also offer protection over lengthening windows of time and with diminishing use rates of active ingredients. Many soilborne pathogens can be sufficiently controlled with a single in-furrow fungicide. Even the most aggressive foliar pathogens (e.g., late blight) can be controlled with a 10-day interval spray program (Figure 1).
Contrary to popular perception, conventional growers are not dousing their crops with pesticides; most chemical-based crop protection products offer good control at minimal quantities. Some modern low-use-rate pesticides are capable of successfully protecting an area the size of a football field with only 2 teaspoons. In spite of the undeniable success of pesticides as an agricultural tool, their role in modern agriculture is not something we can rely upon indefinitely.
Challenges and innovations in pesticide development
To understand the future decline of agricultural pesticides, it is useful to know something about their past and development. The development of modern pesticides has been far more reliant on discovery than creativity. Many of the pesticides in use today were derived from or inspired by a similar molecule found in nature. The pyrethroid class of insecticides was developed after investigating the source of the well-known insecticidal properties of pyrethrum (powdered chrysanthemum petals). The strobilurin class of fungicides generally, and azoxystrobin specifically, is undoubtedly the most widely utilized and successful single-site mode of action fungicide. Azoxystrobin was designed to pattern a molecule called strobilurin A, which was discovered in a pine cone colonizing mushroom called Strobilurus tenacellus. Even the commonly used auxin mimic herbicides – such as 2,4-D and dicamba – were designed to “mimic” the natural plant hormone auxin. No other method of pesticide development has led to more novel modes of action than the discovery of bioactive molecules in nature.
Fungicide discovery trends indicate that our current decade may be the last one to yield a new mode of action (Figure 2), with herbicides and insecticides following closely behind. Increased regulatory pressures have removed certain chemistries entirely from production and excluded other chemistries from being developed. The cost of bringing new pesticides to market has dramatically increased in the corresponding time frame (Figure 3).
Current regulations favor the development of pesticides that are target-specific, with single-site modes of action over broad-spectrum, multisite modes of action. These single-site mode-of-action chemistries are especially vulnerable to being made obsolete through the increasing prevalence of pesticide-resistant pests.
Debatably one of the most iconic lines from the classic 1993 film Jurassic Park is uttered by Dr. Ian Malcom (played by Jeff Goldblum), “Life, uh, finds a way.” Our heavy reliance on pesticides in agriculture has placed selection pressure on the development of resistance. The common phrase “use it or lose it” is dead wrong in regard to pesticide usage. Each time we use a pesticide, we select for resistance in the target pest population and move closer to losing efficacy.
Integrated pest management (IPM) strategies implement multiple approaches for pest mitigation in agricultural systems, including host resistance (e.g., planting disease-tolerant crops); cultural control (e.g., crop rotation); biological control (e.g., releasing insect predators); as well as chemical control methods (e.g., pesticides) (Figure 4). These IPM strategies allow us to decrease pesticide usage and prolong its usefulness. Other practices that prolong the efficacy of pesticides include tank mixing with multiple modes of action and rotating the modes of action used throughout and between growing seasons. Even when implementing all these practices, however, we are merely delaying the pesticide resistance, not preventing it. Our target pests will eventually develop resistance because “Life, uh, finds a way.”
If the development of pesticide resistance is inevitable, why bother implementing IPM? Time. Time is needed to develop and incorporate novel technologies and practices that reduce our reliance on conventional pesticides while extending their lifespan. As an agricultural industry, we have a responsibility to be stewards of the modern pesticides we use and to preserve all we can for as long as we can. In the end, I am optimistic because the phrase, “Life, uh, finds a way,” refers to us as well. Farmers are innovative and quick to adapt to new challenges and adopt new solutions.
Some solutions on the horizon to further integrate pest management are physical technology and advances in biotechnology. Most people think of cold steel as physical technology; however, in modern agriculture, lasers, ultraviolet light and electric fields will be implemented for weed, disease and insect control. Advances in biotechnology are making biocontrol methods more efficacious and feasible as an alternative to conventional pesticides. Viruses designed to infect plant disease-causing bacteria, called phages, are being utilized. Through a method referred to as “spray-induced gene silencing,” strands of RNA molecules are designed, synthesized and sprayed like a conventional pesticide, allowing for highly targeted and effective control of plant pests.
These technologies, among others, make me hopeful for the continuation of our highly efficient and productive agronomic systems, but if all else fails, we can always saw off the top foot or so of a garden hoe and hand it to our grandkids.
