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Diversity Still Matters

A recent article in the Des Moines Sunday Register related that some weeds are now showing resistance to Monsanto’s broad spectrum weed control chemical, Roundup®. Many of our most important crops have now been bred to tolerate Roundup through the marvel of genetic engineering. “Roundup Ready” crops allow farmers to spray right over the crops and eliminate all weeds without further disturbing the soil through cultivation. That saves time, money and helps prevent soil compaction and erosion. Although Monsanto claimed that weed resistance to the chemical was unlikely ever to happen, it has. Many scientists disagreed and said weed resistance was inevitable as “Roundup Ready” crops virtually replaced older genetic lines. Roundup became the one-pass weed control of choice in only a few years and is now being applied to the vast majority of acres in production every year, whether the crop is corn, beans or several others.

Bacteria have long shown their ability to develop resistance to antibiotics in a relatively short time when a few hardier individuals survive an antibiotic attack and pass their stronger resistance on to their offspring. Alternatively, whole populations of bacteria may be exposed to sub-lethal doses of antibiotics over longer spans of time. It’s an oversimplification, but it could be said that they just get used to those lower doses and require ever-higher doses for any effect. Bacteria generational turnover can be as fast as several times an hour; so their ability to develop resistance can happen relatively quickly. Weeds seem to have similar abilities. Most weeds develop only one generation each year, though, so it takes a little longer. Even human beings have shown the ability to develop resistance to certain diseases, but it takes many generations. Many Native American tribes were nearly wiped out by European diseases for which they had no genetic resistance. The diseases spread much faster than in the settlers, whose ancestors had been exposed to those diseases for centuries and had passed on some resistance to them.

I recently borrowed my father-in-law’s copy of a publication called “Noxious and Other Bad Weeds of Iowa.” It was published by the Agricultural Experiment Station – Agricultural Extension Service of Iowa State College in June of 1944. Farmers of the day had quite a variety of tools at their disposal to combat weeds, but chemical weed control was in its infancy. Mechanical cultivation was still their main tool. Although it was time-consuming hard work, it was something weeds could never develop resistance to. There was some art and science to cultivation, though. Timing and using the right cultivation equipment was important in order to do the most damage to specifically targeted weeds and least damage to crops and soil. Some weeds were better attacked in spring and others in the fall. Crop rotations were still important as a means of breaking weed and disease cycles. With the exception of several years that some hay crops offered, no field had the same crop on it two years in a row. Soybeans were just beginning to show up on Iowa farms and joined corn, a variety of small grains and a variety of forage crops in rotations that could see five or more years pass before the same crop appeared in a field again. Multiple cuttings of hay prevented annual and biennial weeds from maturing and making seed. The dense growth of a forage crop, like clover or alfalfa, could smother some weeds, or at least keep their spread in check. They could also select from a range of new chemicals that were generally reserved for spot treatments of difficult perennial weeds. The chemicals were expensive compared to conventional weed control of the day and some were downright dangerous to handle. Particularly bad weed problems might even call for leaving ground “fallowed,” a process that kept all plant growth off the problem area though repeated cultivation for as much as a year to germinate and kill as many weed seeds as possible and weaken the root reserves of perennial weeds. Can you imagine anyone deliberately leaving a field or even a portion of one in fallowed condition today?

There’s no question that farming has come a long way in the past 70 years, but there are some lessons from the past that might be worthwhile to revisit. One of them is the benefit of diversity. Farms in the 40s had diverse crops and diverse livestock. They used diverse techniques to manage them. Diversity gave them the best chance of weathering economic and climate challenges. Diversity allows a prairie plant community with over 200 species to better sustain itself when stressed by climate, diseases or insects than a plant community that has only two crops that are grown in much the same way on millions of acres. We are healthiest when we eat diverse foods and participate in diverse activities. Diversity is the foundation of nature’s health plan, and should still be an important consideration in how we manage the land.

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