Can Herbicide Resistance Evolve due to Factors Other than a Repeated use of Technology? Argentina, A Case to Consider

Herbicide-resistance is one of the main worldwide concerns to farmers and scientists in recent years. In addition, herbicide resistance was declared the principal concern for food production around the world during the 2017 Global Herbicide Resistance Challenge held in Denver. Herbicides are precious resources for sustainable food production, said Dr. Stephen Powles, during his opening lecture at GHRC 2017. He added that 125 million hectares are affected with herbicide resistant weeds, and that only five main Agrochemical companies are still developing new actives to combat these weeds in the future. He concluded that we can, and must, sustain herbicides and other weed control technologies, and that diversity is the key to sustaining those principles. Argentina, as a food supplier, is not exempt from herbicide-resistant weeds, and the increasing rate of area affected in the last five years suggests that nature is ahead of human resources to take control over agroecosystems. A recent, not yet published study, in Argentina, reports that almost 50% of soybean- and corn-growing areas have medium to high infestations of Amaranth species. That translates into 11,500 ha infested by a single genus of weeds. Since the adoption of genetically engineered (GE) crops like soybean (Glycine max), corn (Zea mays) and cotton (Gossypium hirsutum), there has been a shift toward weed species with natural tolerance to herbicides into agrosystems as nature's reaction to the continuous use of a single herbicide, glyphosate. Argentina, like the rest of the world, is fighting weeds in the field with chemistry and with the adoption of new technologies, such as cover crops and crop rotation. Aside from the repeated use of a technology to suppress weeds, many other factors are contributing and entangling the country into a point of no return. In fact, weed resistance to herbicide, as an evolutionary process, sooner or later will be in almost every crop field, but certain "drivers" can accelerate its occurrence if countries like Argentina do not implement rational programs to stop this problem. A lack of public policies, an old legal basis for land leases, and an important change in land management, turned the past farm rotation from grass-fed cattle and crop, into continuous crop soybean monoculture. These factors are threatening the implementation of Integrated Weed Management (IWM), as well as the adoption of Best Management Practices (BMP), to reduce the rate of herbicide resistance cases. Herbicide resistance is growing at a rate of four new species per year. The first cases were due to the continuous use of acetolactate synthase (ALS) chemistry, while current herbicide resistance cases in Argentina are associated primarily with a wide weed spectrum herbicide glyphosate. In addition, the introduction of alfalfa contaminated with palmer amaranth seeds, as well as the ALS-tolerant canola seeds introduced illegally from a foreign country, are gaining hectares as seed dispersal is out of control. Argentina's latest report of weed resistant to 2,4-D dates from 2017, and it is related to a rapeseed biotype (Brassica rapa). Like other countries, Argentina is struggling with a dramatic rate of emergence of herbicide-resistant weeds, but many factors, other than the continuous use of one chemistry, contribute to it. Starting from its past history, Argentina shifted its current field management from rotations, which included pastures and grain production, to cash grain. Cattle are raised in feedlots or otherwise in areas where grains cannot be grown. In addition, in the past twenty years, no-till farming relied on glyphosate for Fall weed management, and residual herbicides were dependent on one single family of chemicals, ALS. As GR soybeans, and later GR corn, entered the market, glyphosate became a cheaper and easier way to manage weeds than any other weed management practice, leading into a larger soybean area, and reliance on a single chemistry, in this case, glyphosate. Herbicide-tolerant weeds are also very hard to control, leading to weed shifts and it is common to find them in mixed populations together with herbicide-resistant species, making it more difficult to decide which weed management plan is better to recommend. In most cases, a sole "driver" weed is not the best strategy. Additionally, incorrect policies applied for the single purpose of tax collection forced Argentinian farmers to grow soybean crop after soybean crop in order to sustain profit. This scenario is even worse when we add the typical Argentinian land tenure, which allows for a one-year lease without any consideration to soil and weed care. When Argentina stops thinking short term, which is directly related to the presidential four-year period, some of these items may be changed to favor management plans to control herbicide-resistant weeds. In other words, adoption of nationwide IWM practices may become a reality if the lease law and exportation tax policy change, together with the real aim of building railways in order to provide cheaper transportation fees.