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Branched broomrape (Phelipanche ramosa) poses a significant challenge to processing tomato production in California. Unlike many other weeds growers manage, broomrape spends nearly 70% of its entire life cycle underground attached directly to tomato roots, before ever becoming visible. By the time shoots emerge above the soil surface, the plant has already been established belowground for weeks. Once it emerges, it can flower and produce seed within a couple of weeks.

Branched broomrape is a parasitic weed that continues to challenge processing tomato production in California. Nearly 70% of its lifecycle is completed underground; once it emerges, it can flower and set seed within just a few weeks. Current best management practice recommendations for broomrape management in conventional processing tomatoes includes a herbicide treatment regime to control early-stage broomrape at the time of root attachment and removal of emerged plants before they set seed.

It is with great sadness that we share the passing of Dr. Jodie Holt, a longtime faculty member in the Department of Botany and Plant Sciences at UC Riverside, who passed away April 27, 2026.

California’s processing tomato industry, for the first time this past harvest season, agreed to voluntary equipment cleaning and notification guidelines to prevent the spread of branched broomrape, a parasitic weed that attaches to roots and sucks out key nutrients. 

Some of my weed science extension colleagues in the midwest have a podcast called War Against Weeds  supported with funding from the North Central IPM Center.  I was interviewed on the podcast a few years ago about herbicide resistant weeds in orchards.  Earlier this week, they invited me back as the first interviewee of their 11th season where we talked about branched broomrape in California processing tomato.  

UCCE Sutter–Yuba is pleased to announce the launch of a new collaborative project with the Sutter and Yuba County Agricultural Commissioners’ Offices focused on the identification and management of invasive weed species in the region. As part of this effort, this project will be coordinating ongoing mapping and treatment efforts and recruitment of stakeholders.

The use of walnut leaf biomass as a natural mulch and an eco-friendly practice can help prevent weed seed germination by excluding light and/or acting as a physical barrier that prevents weed emergence. Beyond that, several studies have shown potential allelopathic effects of juglone and leaf extracts of walnut on seed germination and seedling root and shoot growth (Kocacë and Terzi, 2001; Zhang et al., 2008; Chauhan et al., 2022; Đorđević et al., 2022).

Fig. 1. Walnut leaf mulch small plots trial as a low-input strategy for weed management.

To provide better recommendations on how to best use rimsulfuron and other residual herbicides to target johnsongrass I established a set of trials in Shasta and Tehama county prune and walnut orchards in winter and spring of 2025. I had two primary goals: first, to test if early spring rimsulfuron applications were effective for control of johnsongrass and second, to determine whether treatments were primarily affecting seedlings or established populations.

Weed Science School is less than two weeks away! Join the UC Davis Weed Research and Information Center for this 2.5 day course. Learn through lectures and laboratory demonstrations at the Bowley Plant Science Teaching Facility at 1200 Extension Center Drive in Davis, CA on September 16-18, 2025.