UC Cooperative Extension weed advisor John Roncoroni retires

John Roncoroni examines silver leaf nightshade that he found in a vineyard.

After 38 years of service, John Roncoroni, UC Cooperative Extension advisor specializing in vineyard weed management in Napa County, plans to retire July 1.

Over the years, Woodland native Roncoroni has become a trusted resource for weed management research and extension, not only in the North Coast, but throughout California, which is home to 500,000 acres of premium winegrapes. He is known for his research on conventional and organic herbicides, hedgerows in vineyards, irrigation pond weed control, and sheep for grazing weeds in commercial trees and vines.

“Over the years working with John Roncoroni, I experienced firsthand his dedication, passion and knowledge to educate farmers and agricultural workers – both in English and Spanish – about best management practices to control and eradicate invasive weeds and weeds of concerns for the agricultural industry. John will be missed greatly by the agricultural industry and by the people whose lives he touched,” said Jose Chang, Monterey County assistant agricultural commissioner and former deputy agricultural commissioner in Napa County.

After earning a B.S. in environmental policy analysis and planning with an emphasis in agriculture at UC Davis, Roncoroni began his career as a UC Davis postgraduate researcher in 1983, then became a staff research associate working with other weed scientists in crops, forest and rangelands. He earned an M.S. in horticulture at UC Davis in 1999.

“It was my 20-year association with UCCE weed specialist Clyde Elmore that set me on the path to becoming a UCCE weed science advisor,” Roncoroni said. While collaborating on a USDA-funded project to investigate chemical and non-chemical alternatives to methyl bromide, he learned about biofumigation and other alternative pest control methods. 

From 2003 to 2007, Roncoroni served as IR-4 Field Research Center director, testing pesticides to be submitted for EPA registration.

In 2007, when Roncoroni joined UC Agriculture and Natural Resources as a UC Cooperative Extension advisor in Napa County, most conventional grape growers used glyphosate, or Roundup, for the weed control.

“In fact, Roundup only was considered the most sustainable weed management method,” Roncoroni said. “This overreliance on glyphosate resulted in biological resistance by weeds.” 

He taught growers about alternative herbicides and non-chemical weed control methods and how to make these methods more effective. Little did he know that this research would become even more valuable when some consumers began to object to glyphosate use.

“It was my 20-year association with UCCE weed specialist Clyde Elmore that set me on the path to becoming a UCCE weed science advisor,” Roncoroni said.

Roncoroni shares his research results through field days, trade publications and newsletters. He was the lead author of the weed management section of the UC IPM Grape Pest Management guidelines. 

“My biggest impact came through in-person presentations,” Roncoroni said. “This is where I gained the trust of the California wine grape industry. He has traveled throughout the state and to Colorado, Texas and Oregon to share his knowledge.

Because he has studied weed management in a broad array of environments, Roncoroni is often asked by UCCE colleagues to give weed control tips to different audiences ranging from golf course turf managers to small-scale Mien strawberry farmers.

“Over the years I have had the opportunity to work on weed control in forestry, rangeland, row crops, alfalfa, fruit and nut trees  but it was my early training in weed management in turf and ornamentals, mulches and alternative weed control that added to my effectiveness in teaching weed control to urban audiences and to training UC Master Gardeners,” said Roncoroni, who has trained more than 1,700 UC Master Gardener volunteers in weed identification, biology and management.

Roncoroni's expertise has been recognized by the California Sustainable Winegrowing Alliance, which asked him assist in writing their standards for sustainable winegrowing, and the California Department of Pesticide Regulation, which asked him to serve on its Pest Management Advisory Committee. In 2018, the California Weed Science Society named Roncoroni an Honorary member, its highest honor.

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