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Parasitic weeds threaten California tomato farms

At first glance, Orobanche ramosa looks like an interesting blossoming plant, one that could add a unique flair to flower arrangements. But it’s a parasitic weed that attaches to roots, sucks out nutrients, and is threatening California’s $1.5 billion processing tomato industry.

The weed’s tiny seeds — smaller than finely ground pepper — can survive in the soil for many decades and be carried by the wind, water, soil transfers, and even footwear. If found attached to crop plants and reported to the state, farmers are required to destroy the field before harvest, taking large losses not covered by crop insurance.

Its resurgence concerns state regulators and industry, which is helping fund multidisciplinary research at the University of California, Davis, on ways to detect, manage, and fight the weed.

“Most of the damage occurs before you can see it,” said Brad Hanson, a professor of Cooperative Extension in the Department of Plant Sciences. “There’s a lot of ripples to the problem. We could see it spread to other crops and other regions in the state if it’s not managed.”

Across three colleges at UC Davis, researchers are working on ways to detect the pest, manage it in the field throughout its life cycle, and develop long-term solutions to minimize the threat to California agriculture. The work is happening in labs and the field, using drones, human spotters, and new techniques to sniff out volatile organic chemicals that are emitted when the weed is present.

They are also testing ways to sanitize farm equipment to reduce the risk of spreading seeds from contaminated fields to clean ones. And they are testing dozens of other crops to see if they are susceptible or could be used as false hosts to kill off the Orobanche seeds in the soil.

Invasive species alert: A weed resurgence in California agriculture
The California Department of Food and Agriculture and industry had a program from the 1950s through the 1970s to eradicate the weed, which is commonly known as branched broomrape. But the weed showed up again in Yolo County in 2017.

Brad Hanson, a professor of Cooperative Extension in the UC Davis Department of Plant Sciences, examines a stock of Orobanche ramosa pulled from off a tomato plant in nearby Woodland, where scientists are studying the parasitic weed. (Emily C. Dooley/UC Davis)
At high infestation levels, Orobanche can reduce crop yields by as much as 80%, which is a tremendous threat considering California farmers grow roughly 95% of all processed tomatoes — for pizza sauce, soups, tomato paste — in the nation.

“Believing it to be eradicated, the industry moved on to other challenges,” said Zach Bagley, managing director for the California Tomato Research Institute Inc., or CTRI. “We’ve been aggressive, with this as our top priority, and we’ve been putting the funding behind it.”

Read the complete article here.

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