Environment

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.

In California, the Department of Pesticide Regulation (DPR) has a license and certification system which allows for professionals to apply pesticides as a part of their job duties. While everyone using pesticides must follow all directions on the pesticide label, as well as any additional state or local regulations, professional applicators need to follow additional regulations. Most employees who spray pesticides hold a qualified applicator license (QAL) or qualified applicator certificate (QAC).

Introduction

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

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.

This year in Southern California the rainy season got off to a late start. Southern California has received about one half of the average precipitation total as of this writing (and that's not an April fool's joke). Last year we had over 50% more rainfall than the historic average, it was a wet year. Most of inland Southern California receives about 12 inches of rainfall in an average year, this year we've had less than 6 inches and last year we had about 16 inches.

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”?

A recommendation bulletin has been released for florpyrauxifen-benzyl (Loyant® CA, Corteva Agriscience LLC, Indianapolis, IN, USA) to control cattail plants in California rice fields and permitted under FIFRA Section 2(ee). Cattail (Typha latifolia L.) also known as common cattail or broadleaf cattail is a perennial wetland weed that naturally occurs widely in nearly all North America and are often considered undesirable, weedy, or invasive. Common cattail is cosmopolitan weed that can grow up to 10-ft tall under favorable conditions.

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