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When Tall and Skinny Isn’t Good

My hour commute from St. Matthews to Sumter is visually interesting. From the top of Hwy. 601 just  as I begin the descent to the bridge (being replaced by a new one two feet away from the existing one), I can see both the SCE&G Wateree Power Plant and  International Paper's steam/smoke stacks; the only signs of civilization in an otherwise uninterrupted view of the Congaree River Swamp. Before and after the bridge crossing, fields of cotton, peanuts, and occasional soybean plantings predominate.

Row crops have been bred to be the same height, mature at the same time, and share other specific traits. In the past decade, with the advent of “Round-Up Ready” seeds, the fields were perfect examples of genetically identical monocrops with nary a weed in sight. But not anymore. Tall and skinny amaranth plants stand out like really bad sore thumbs in the less carefully managed fields. Round-Up is  a commercial name for glyphosate, a non-selective herbicide that normally kills any plant on which it is sprayed. Cotton, corn, soybeans, and other plants have been genetically modified to be resistant to glyphosate, so farmers could spray over the top of emerged fields, killing weeds but sparing the desired crop.

Palmer amaranth, a.k.a. pigweed, has developed resistance to Round-Up. It is a dioecious plant; male and female flowers appear on separate individuals. Male plants produce copious amounts of pollen, which is carried by wind to female flowers. Lots and lots of pollen, lots of mixed up pollination; all these factors lead to genetic diversity. Certain seeds inherited the genetic mix that gave them resistance to Round-Up (glyphosate) and they were not killed by over-the-top herbicide sprays. Since they were the only players in the game left standing, their offspring didn’t have to compete with other weeds and so came to dominate the seed bank.

For five or six years, the “Round-Up Ready” seeds allowed farmers to use glyphosate as their total weed control program. Now, the management aspect is back. And the most common tool used right now is roughing. Imagine farm workers in a field! It’s a surprising sight to see a gang of six or so workers going through a 200-acre field pulling or hoeing out amaranth and removing those plants from the crop. If just cut off, or even if pulled and left on the ground, it re-sprouts or re-attaches and grows again. Farmers are having to use many different pre- and post-emergent herbicides combined with other management techniques, all of which add to the cost of production, in order to control this noxious weed. 

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