For centuries, farmers have used sheep to graze down unwanted vegetation but, unfortunately, the animals would also snack on crops. So the University of California Cooperative Extension is trying to teach the animals more useful eating habits.

"We have a project to train sheep to have an aversion to grape leaves," said Morgan Doran, Solano County livestock advisor and project leader. "If sheep avoid grapes, they can graze the floor of a vineyard, providing farmers an alternative to using herbicides and mowing."

Following the recommendations of noted animal behaviorist Fred Provenza of Utah State University, the researchers let sheep eat their fill of grape leaves, and then administered a small, harmless dose of a medicine that made them nauseous.

"The sheep experience a brief period of malaise," Doran said. "They recover quickly, but they don't seem to forget, even after nine months."

Initial field observations at the UC Hopland Research and Extension Center, south of Ukiah, showed that, unlike their untrained counterparts, the trained sheep did not like immature grapes or grape leaves.

Sheep weed control is adaptable to various weather conditions. During a rainy year, when muddy vineyards prevent tractors from mowing or applying herbicides, the sheep can still graze the weeds. And in dry years, when range forage is scarce, the vineyard weeds provide an additional food source. Researchers say this method could likely also be applied in orchards.

The sheep grape-leaf aversion project, funded with a UC Division of Agriculture and Natural Resources grant, involved the following UC Cooperative Extension farm advisors: Doran of Solano County, Stephanie Larson of Sonoma County, Roger Ingram of Placer and Nevada counties, John Harper and Glenn McGourty of Mendocino County, Ed Weber of Napa County, and Associate Professor Emilio Laca and Cooperative Extension Specialist Mel George of UC Davis.