A Reuters News Service article about increasing resistance in weeds that impact crop production in the U.S. caught my attention recently. The article stated that many weeds are developing resistance to herbicides like Roundup, produced by Bayer AG and over 70 herbicides that chemical company Corteva, markets. According to the article, weeds are evolving resistance faster than these companies can change their formulations to combat them. Reports of herbicide resistance have cascaded since the first reported case of herbicide resistance in the United States in 1964, when field bindweed in Kansas was found to be resistant to the common broadleaf herbicide 2-4-D. By 1970, the weedy plant common groundsel was found to be resistant to Atrazine, a common herbicide in the triazine class of chemicals that has been used for control of weeds in corn, sugar cane, sorghum and pineapples since the 1960s. Scientists report that beginning in the 1980s, the number of resistant weed bio-types began increasing rapidly in the U.S. and worldwide. Resistance to one or more of the 25 herbicide families has been observed in at least 65 weed species in the U.S, and the International Herbicide-Resistant Weed Database reports that there are currently 530 unique cases of herbicide resistant weeds globally, and weeds have evolved resistance to168 different herbicides in 100 crops in 72 countries. So far, no magic bullet has been developed. For example, already, 21 weed species globally have shown resistance to dicamba, the most recent major U.S. chemical, which was made available to farmers in 2017, but which has also been implicated in numerous cases of pesticide drift from application sites to adjacent fields and orchards, causing thousands of dollars in damage to those non-target crops. Not only are many weed species very adaptable to a variety of soil and climates, they are able to produce a lot of seeds, which helps them to spread. For example, the common weed Kochia, spreads as many as 30,000 seeds per plant, which can cut soybean yields by 70% if it’s not controlled. But many scientists expect weed problems to worsen, because some weeds show resistance to chemicals even on the first exposure to herbicides. If farmers don’t control those surviving weeds population of resistant weeds they’re likely to make weed control more difficult over time.
Up until the late 1950s and early 1960s, farmers controlled weeds by mechanical cultivation using hoes, or equipment drawn by either horses or tractors that disturbed the soil in between the crop rows, which killed the weeds. Some farmers are quick to point out that no weeds are resistant to steel, so in addition to cultivation, good farmers walk crop rows to rouge out surviving weeds, or hire teenagers to do the job. However, when chemical control of weeds became commonplace in the 50s and 60’s many farmers became complacent about weed control. When a few weeds were left standing in their fields, they didn’t worry, since most of the weeds were gone with one pass of a sprayer. Besides, less time cultivating fields allowed them to rent more land and spread their investment in equipment across across more acres.
The bottom line is that in the future, farmers may need to pay closer attention to what’s happening in their fields, and not depend on magic seeds or potions to do the job.
