“What about the edible weeds?� I asked, near the end of a pleasant day, chatting with a group of friendly, articulate smallholders near Retalhuleu, in lowland Guatemala. They had collected wild plants from the area, and taught Keith Andrews and I about each one. But I knew from the literature that many wild plants in Guatemala and southern Mexico are “quelites� or edible weeds, nutritious, leafy vegetables that grow wild in the maize field.

Then the people explained with a touch of sadness how they had completely lost the wild edible greens that once grew abundantly. “When we started to use herbicides, the quelites disappeared completely.�

At four sites around Guatemala, wherever people had adopted herbicides, they had selected for a tough, robust community of weeds that were hard to kill and good for nothing.

The community of Palestina, in near the wondrous Lake Panajachel, was one of the places that did not use herbicides. As the local people walked with us around their fields and gardens, they spontaneously picked wild plants to take home. Most of the plants had uses.

And while ethno-botanists often like to write about medicinal plants and leafy vegetables, by far the most common use of edible weeds is as livestock fodder. These weeds for feed come at the most crucial time (for people and their animals), before the harvest. When the stored food has been eaten up and the new crop is not quite ripe yet. Edible weeds supplement the food of people, but they tide the animals over the hungry season.

Hand weeding a corn field with a hoe is tedious and backbreaking. Herbicides are like a magic wand. The farmer straps on the backpack sprayer, pumps it up and waves the wand over the weeds, while the herbicide solution springs like a mist from the nozzle on the end, and makes all the hard work vanish.

Then Darwinian selection sets in and a niche is opened up for the most notorious, herbicide-resistant weeds that nature has in stock. The delicate weeds, the ones that people and animals can eat, simply can’t compete.

For a study of local knowledge of agriculture in Guatemala (Dos Saberes, by Jeff Bentley and Keith Andrews, in Spanish) see: http://www.iica.int/Esp/regiones/central/guatemala/Paginas/Publicaciones.aspx