UC Weed Science (weed control, management, ecology, and minutia)
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Chemigation Alternatives for Branched Broomrape Control in Processing Tomato: Promising Steps Forward

Branched broomrape (Phelipanche ramosa) is an invasive parasitic plant that poses a significant threat to California’s processing tomato industry. Known for its ability to attach to and draw nutrients from host roots, this pest can cause yield losses and trigger strict quarantine measures in California commercial fields. Building on Israel’s PICKIT approach for Egyptian broomrape (P. aegyptiaca), California researchers are working to adapt and refine chemigation-based herbicide strategies that target this challenging weed without harming tomato crops. 

A portion of this research was recently published in HortScience Volume 60, Issue 7, and can be viewed here: DOI: 10.21273/HORTSCI18497-25

Why Chemigation?

Chemigation—applying herbicides through drip irrigation—offers a targeted approach to control parasitic weeds like broomrape, which attach to the host’s roots and are difficult to manage with conventional herbicides. This method has shown success in controlling Egyptian broomrape in Israel, and researchers have been evaluating its potential against branched broomrape in California and Chile for the past several years.

Research Objectives

The research team aimed to:

  • Identify chemigation herbicide programs that suppress broomrape emergence.
  • Ensure crop safety—avoiding phytotoxicity or yield loss in tomatoes.
  • Explore options that could be implemented under California regulations.

Field trials were conducted over multiple years in California and Chile, testing several herbicide combinations, rates, and application timings.

 

Key Treatments Evaluated:

  1. Preplant Incorporated (PPI) Sulfosulfuron followed by Chemigated Imazapic
  2. Chemigated Imazamox (with or without PPI Sulfosulfuron)
  3. Chemigated Rimsulfuron (with or without PPI Sulfosulfuron and plant defense activator acibenzolar-S-methyl)
 

What Did We Learn?

Crop Safety:

  • Imazapic (used in Israel) reduced broomrape emergence and was safe for tomatoes but will not be registered in California or Chile.
  • Imazamox caused unacceptable crop injury at higher rates in some trials, limiting its suitability for this use case and it will not be registered.
  • Rimsulfuron, chemigated multiple times, proved consistently safe for tomato plants across all trials.

Broomrape Control:

  • A Rimsulfuron chemigation program significantly reduced broomrape emergence in California field trials.
  • Imazapic + sulfosulfuron was effective but faces regulatory barriers in California and Chile.
  • Imazamox showed variable efficacy and had insufficient crop safety.

Where Do We Go from Here?

The most promising outcome of this research is the development and registration of chemigated rimsulfuron for broomrape control in California processing tomato under a 24(c) Special Local Needs label. This tool offers growers an effective, crop-safe solution for this difficult-to-control parasitic weed.

Future work will:

  • Fine-tune application timing and rates.
  • Pursue international registration efforts, including in Chile.
  • Integrate chemigation into tomato weed management programs for broad-spectrum weed control

Conclusion

While broomrape remains a challenging pest, this research brings practical new tools to the table. Chemigated rimsulfuron offers strong suppression with excellent crop safety and is now an available option for California tomato growers facing broomrape pressure.

For more information on the use of chemigated rimsulfuron for broomrape management in California processing tomatoes, visit the UC Weed Science blog.Top of Form