A bucolic scene that hearkens back to antiquity is being played out at the University of California Hopland Research and Extension Center, south of Ukiah. Sheep lazily graze in a vineyard, munching on weeds growing between the vines.

Sheep have been used by farmers for centuries to control unwanted vegetation, but there was always a tradeoff. In addition to keeping down weeds, unknowing sheep would snack on the crop itself. So UC Cooperative Extension is trying to give the animals an education.

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

To change the animals’ diet preference, the researchers consulted with noted animal behaviorist Fred Provenza of Utah State University.

“We often see livestock and wildlife as eating machines and don’t understand that an animal’s history influences its diet and habitat preferences,” Provenza said.

Provenza said animals learn from social interactions with their mothers, peers and people; feedback from nutrients and toxins in plants; and interactions with their physical environment, including location of water and predators.

“Behavioral principles can provide solutions to problems faced by producers and land managers,” he said.

Based on Provenza’s extensive research on animal behavior, the UC Cooperative Extension researchers allowed sheep to eat their fill of grape leaves, then administered a small dose of lithium chloride, a harmless medicine that creates the sensation of tummy trouble.

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

Field observations promising

Initial field observations of trained sheep show they don’t like immature grapes or grape leaves, while their untrained counterparts do. In the Hopland vineyard, Doran pointed to a grapevine with very little new growth. “This vine was exposed to sheep that hadn’t been trained,” Doran said. “We see a lot of damage on this. Most of the vine shoots were 10 or 12 inches high. Now they’re gone.”

In another part of the vineyard, sheep that received training ignored the grape leaves and emerging fruit, concentrating instead on eating weeds.

The sheep training research has many potential benefits for grape producers and sheep herd managers. Sheep weed control fits guidelines for organic production, in which no artificial pesticides or fertilizers are used, and biodynamic production, a system that builds on the organic philosophy with additional natural and holistic management practices. Conventional farmers may also want to look into the use of trained sheep for vegetation management.

“In very wet years, farmers may not be able to get tractors into the vineyard to mow or apply herbicides,” Doran said. “The sheep can easily get in and clear the vegetation regardless of mud and rain.”

In dry years, vineyards provide an additional food source for sheep.

“There is a tremendous amount of feed growing on the floor of the vineyard, so it gives a sheep producer an alternative feed source when traditional feed sources on the range may be low. The producer can then conserve food for the summer or fall,” Doran said.

The farm advisors working on the project believe their research could have far-ranging implications, including orchard weed management and making use of the space between trees in a young planting to grow livestock feed.

The sheep grape leaf aversion project is funded with a grant from the UC Division of Agriculture and Natural Resources. Farm advisors involved, in addition to Doran, are Roger Ingram of Placer and Nevada counties, Stephanie Larson of Sonoma County, John Harper and Glenn McGourty of Mendocino County and Ed Weber of Napa County, and Associate Professor Emilio Laca and CE Specialist Mel George of UC Davis.