Notes from the Land Where Pigweed is King

Written By David S. Shields

Originally Published in the Rice Paper Newsletter, Spring 2012


An edible plant is stalking the south, muscling in on soybean and cotton fields, invading corn plantings and sweet potato beds. Designated Amaranthus palmeri by botanists, farmers with increasing dread use an uglier name — pigweed. It has become many a Southern planter’s worst nightmare.

The fact that the leaves, stems, and abundant seeds are edible, indeed extremely nutritious, matters little. Aside from health food devotees, Palmer amaranth seeds have no market in North America. The leaves concentrate too much nitrogen as nitrate to be safe as animal fodder. So the Southern farmer reckons it a weed. More than a weed — a super plant, indigenous to southern soil and climate, that has evolved into an extremely prolific reproducer, generating massive seed heads. A single plant in a cultivated field produces over 150,000 seeds; with no competition, 1.5 million seeds. Its vitality and profusion enable it to take over a field in two seasons.

Sometime in the last six years it developed resistance to the commonest chemical herbicide in use, Monsanto’s RoundUp. It would appear that the warnings of the critics of conventional agriculture have come true. Exclusive reliance on a single herbicide year after year has produced mutations in Amarantahus palmeri so that since 2005 Glysophate, the active agent in RoundUp no longer inhibits the growth of pigweed. Calls for rotation of herbicides in a field each year to prevent the development of resistant species went unheeded, in part because salesmen touted RoundUp as a never-fail herbicide. 

The season of regret has arrived. Farmers are forced to resort to a stop-gap: manual removal of young pigweed stalks by hired labor gangs. Unfortunately labor is not always available in season. Unfortunately the overlooking of a single stalk when clearing is enough to put a field in peril.

On one level, it is odd that the world does not welcome a food source that has become so vital that it has decided to plant itself in all the fields we have prepared for the convenient culture of produce. Yet the United States seems to lack a 21st century George Washington Carver who can teach the present generation to find favor in amaranth. So we seem fated to relive recent history with agricultural chemists concocting new cocktails of plant toxins (Dual, Valor, Authority MTZ, Envive) to spread on soil before planting.

One hopes that exploration of rotations is undertaken. Pigweed’s efficiency pulling nitrogen out of the soil bodes ill for its prolonged colonization of an area, since its own vitality is taxed by the nutriment exhaustion with each successive year. Pigweed thrives when fields are cultivated with the same crop in succession. Weed scientists Bob Scott and Ken Smith of the University of Arkansas have noted that regular crop rotation inhibits pigweed’s consolidation: “Although Palmer amaranth plants produce a tremendous number of seed, the seed do not live long in the soil. One to two years of an alternate crop that can be kept Palmer amaranth-free will significantly reduce the population level of pigweeds.”

What will happen next? When Science magazine in 1977 proclaimed Amaranth the “plant of the future” it thought that its contribution to world nutrition would make it needful in areas where population stress and degraded soil prevailed. It hardly imagined it would become the scourge of American farmers. Yet all its promise remains as well as all its peril. 

One thing is sure, the plant will receive a scrutiny it has never heretofore endured, and from this careful examination, knowledge will surely arise of its potential for improvement, its natural limitations, and the vulnerabilities that will enable its spread to be controlled. For many Southern farmers this knowledge can’t come too quickly.