Most annual crops are derived from weedy plants. Weeds are as much a part of the crop complex as the crops themselves, providing genetic material for crops. Historically, weeds and crops move back and forth, what's a weed becomes a crop, and sometimes, crops again become weeds.

Vetch (Vicia spp.) provides a good example. It was grown traditionally in forage mixes, but largely disaappeared with the advent of industrial agriculture. Now there is renewed interest in it for use in forages, and also as a cover crop. The greatest reservoir of diversity resides in the weedy populations.

At left, the four seed vetch (Vicia tetrasperma) grows as a weed on winter wheat in Nova Scotia. It has a biennial lifecycle and tends to get established on crops such as winter wheat that also have a binennial life cycle.

At right hairy vetch (Vicia villosa) was planted with winter rye on Oak Manor farm in Ontario. Both have a biennial life cycle. The farmer was growing the vetch to obtain seed for use as a cover crop and in forage mixtures. The long stemmed winter rye serves as a trellis for the viney vetch. They both mature at the same time and are harvested together; the two seed types are separated mechanically.

At left hairy vetch was sown as a cover crop. It was sown into a field of winter wheat in Ontario in the spring, and grows vigorously after the wheat was harvested in early August. Vetch is a legume, so also adds nitrogen to the system.