THE NEEDLE IN THE HAYSTACK: KEEPING IT LOST. F. Forcella*; USDA, Morris, MN (263)
A recent advertisement on American commercial television depicts a well-dressed young man reaching into a haystack. In less than a second he removes his hand from the straw and briefly examines something held between his thumb and forefinger. With feigned surprise and a slight smirk, he quips, “Huh, found it.” Needle in a haystack, resistance in a population, one in a billion: all seem equally rare. Why then are there so many resistant weeds nowadays, and how might we prevent even more of them? Explicit answers are in other reports associated with the “Nonchemical Tactics in Herbicide Resistance Management” symposium, and they will not be listed here. Instead, two ideas related to the symposium topic, but only marginally related to one another, will be explored here. Hopefully each will be at least entertaining if not informative for the audience. The first topic involves the human dimensions of resistance prevention and management. In other words, we know what is necessary, so why don’t we do it? The second describes a new form of physical weed control, air-propelled abrasive grit. It is not a panacea for resistance management, but merely one more little hammer among many in the toolbox. In the agricultural system that has evolved in the USA, weed scientists interact with individuals and groups positioned at many different levels. Weed scientists basically serve as coaches to these entities, who effectively are our clients. Coaches must ask who their clients are (growers, policy makers, etc.), in what manner they relate to them, whether client behavior should be changed, and if so, how? If change is desired, there are three basic elements to it: the desire to change, the ability to change, and in some cases at least, permission to change. Desire is affected by awareness and perception. Extension educators have developed highly informative materials for making growers aware of resistance issues, but not all growers perceive the issue similarly. Some behaviorists link the desire to change inversely with wealth; i.e. change could kill the goose that lays golden eggs. The ability to change agronomic behaviors has three components: psychological, financial, and environmental. Fear of change is paralyzing for some. Change may not be feasible for others if it entails even short-term reductions in net income. And growers on gumbo soils, for example, simply have fewer options for successful change than growers with soils that are more versatile. Permission to change involves consent from higher authorities. Land owners, bankers, regulators, etc. can stymie change regardless of preferences of growers. Behaviorists suggest that the outcome of coach/client relationships reflects upon both the client and the coach, not just the client imperfectly following the coach’s advice. Thus, weed scientists may have to inquire, “How have we contributed to the issue at hand?” Behaviorists also talk about “force fields,” with multiple and opposing driving and restraining forces. Have weed scientists unwittingly had a hand in both? Can the identification and measurement of those forces assist in affecting the change that is needed to keep needles lost? Physical weed control likely will never exceed the efficacy and efficiency of chemical control. Nevertheless, some physical control methods are very effective. Many of these techniques involve soil disturbance, and therein reside the problems of organic matter losses, erodible soils, and greenhouse gas emissions. Air-propelled abrasive grit may help alleviate this problem for both in-row and between-row, selective, postemergence control without cultivation. Grit can be derived from agricultural residues (corn cobs, nut shells), organically approved fertilizers (alfalfa meal, corn gluten meal, seed meals, poultry manure), mineral fertilizers (lime, gypsum), and bioenergy residues (dried distillers grain, biochar). Nutrient- and carbon-laden grit not only affects weed control, but also supplies needed fertilizers to crops and adds stable forms of carbon to soil. Two timely applications of grit, totaling about 1000 kg ha-1, provide season-long weed control in field corn and maintain high crop yields. Abrasive grit never will replace herbicides, but in situations where non-chemical and non-soil disturbing forms of control are needed, it represents a potential solution. In so doing, it can assist with limiting new incidences of herbicide resistance and help control populations already resistant.