Wine grape vineyards and pear tree orchards in California's North Coast region are increasingly falling victim to oak root fungus, a disease commonly found in wildlands oak trees. UC Davis plant disease experts suspect that sprinkler irrigation in vineyards and orchards may be encouraging the spread of the disease from dead or dying oak trees. The disease is caused by the armillaria fungus. Spread underground by root-to-root contact, it can remain in the soil for nearly 100 years, according to David Rizzo, an assistant professor of plant pathology. While oak trees in the wild normally undergo seasonal water cycles, including droughts, the irrigation of vineyards and orchards encourages constant soil moisture in which the fungal disease thrives. Until disease-resistant rootstocks for trees and vines are available, growers' best defense against the disease is to remove damaged trees and perhaps reduce the amount of irrigation water applied to vineyards and orchards bordering wildlands forests. Rizzo and his research team are currently studying the genetic makeup of wild grapevines growing along rivers and streams for possible answers to the oak root fungus problem.