Observations show that maize field weeds are an important resource in rural areas of Mexico, especially in the high valleys of the south-central part of the country. They are used as quelites (spinach-like vegetables), fodder, ornamentals and a nectar source for bees. We attempted to quantify and evaluate these uses in economic terms for an area that is neither very traditional, nor very modernized. San Bartolo del Llano is a village in the northwest of the Valley of Toluca, with a relatively productive, irrigation-supported, maize-based agriculture, with fertilizer, herbicide and some mechanization inputs, but traditional maize varieties. Also, smallscale, double-purpose cattle breeding is widespread. We interviewed 24 families weekly during a whole growing season on their use of weeds for food and fodder (the other uses were minor) and calibrated quantitiy measures. In one family, all weeds used were measured. Also, we obtained data on prices and costs. The results show that fodder is the dominant use in economic terms, and that it elevates the economic value of the useful biomass of the maize field by an average of 50%, with a potential that is even higher. The fodder is harvested between July and October, when the critical period of competition between maize and weeds is over.

Key words: maize, Mexico, quantitative ethnobotany, Valley of Toluca, weeds