Mar 28, 2025

UC Davis research improves weed control in orchards and specialty crops

Weed control in orchards and specialty crops remains a constant challenge for growers, requiring careful planning and smart management to stay ahead of persistent weeds.

“Weeds are a year-in, year-out problem,” said Brad Hanson, cooperative Extension weed specialist at UC Davis’ Department of Plant Sciences. “Weeds are always in the top five issues of growers. If you’re a farm or crop manager, weeds are right in front of you every week of the year.”

Weed research at UC Davis

Hanson emphasizes the importance of growers knowing the weeds in their fields and making targeted, thoughtful management decisions.

Broomrape threatens tomatoes

In California, branched broomrape has become a top concern in processing tomatoes. This parasitic weed attaches to plant roots, drawing water and nutrients while producing thousands of seeds.

And, as a federal and state quarantine pest, broomrape-infested fields often face crop destruction and regularly hold orders.

“The regulatory status poses a huge economic challenge,” Hanson said. “It’s probably the number one issue of processing tomatoes.”

The Hanson Weed Management Lab has spent years refining herbicide protocols to help control broomrape, including work that led to a special local needs label for Matrix herbicide. Growers have reported favorable results from this treatment, and Hanson’s team continues to explore other chemical options for broomrape management.

Preventing spread through sanitation

To limit the risk of spreading broomrape seeds and other soil-borne pests, UC Davis researchers are developing sanitation protocols for farm equipment. Collaborators in plant pathology are helping test chemical sanitizers and cleaning methods for harvesters, trucks, trailers, and tillage equipment.

“The main focus of the sanitation work is to reduce the risk of rapid and long-distance spread of serious pest problems through the industry,” Hanson said.

Weed control in orchards and beyond

Beyond tomatoes, weed pressure remains a priority in orchards and vineyards. Hanson notes that low commodity pricing has reduced herbicide use in almonds and walnuts, prompting growers to rethink what level of control is necessary.

While 100% weed control was once standard, growers now aim for effective but more economical thresholds.

“It’s really just smart decision-making,” Hanson said. “Know your weeds, choose the right tools, and use them effectively.” He cautions growers against using the wrong methods: “Using the wrong tools to do the job, no matter how big the hammer you have, is not going to get you success.”

Weed control in orchards requires a flexible, field-specific approach. By identifying target weeds, setting realistic goals, and selecting the right strategies, growers can manage weeds while balancing costs, time, and crop health.

— Doug Ohlemeier, Assistant Editor