Science & Technology

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.

The California Weed Science Society (CWSS) publishes a twice-yearly "CWSS Research Update and News" newsletter as one of the society's publications.  The July 2025 issue just went online and is available here: https://cwss.org/wp-content/uploads/2025/07/CWSS_Research_Update-July-2025.pdf

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.

Branched broomrape (Phelipanche ramosa) continues to challenge California’s processing tomato industry, particularly in the Sacramento Valley. As a parasitic plant that attaches to tomato roots, its presence threatens both yield and export market access. In a recently published study in Weed Technology, we evaluated the efficacy of chemigated rimsulfuron—a recently registered approach with potential to offer targeted, soil-based suppression of this invasive pest.

Calibration might sound intimidating, but it’s critical for safe and effective herbicide application. Proper calibration ensures that the correct amount of pesticide is applied to an area while achieving the desired level of pest control. To support land managers and pesticide applicators, the UC Statewide Integrated Pest Management Program, in collaboration with the California Invasive Plant Council, has released a new online course: Herbicide Application Calibration for Non-Agricultural Sites.

Sharing a recent post from the California Invasive Plant Council (Cal-IPC) about a new page on the WeedCUT online decision support tool.

-Brad

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New WeedCUT Feature: BMPs for Herbicide Application Techniques

Confused about what a “drizzle” application is and when to use it? Deciding on the best way to estimate your application rate when using a backpack sprayer? Wondering what your hole spacing should be when using “drill-and-fill”?