Walnut production comes with real challenges, including rising input costs, extreme weather and pest pressures, all while grower returns are constrained due to global supply. While there is no silver bullet solution, production and postharvest research is an important tool to help the industry make progress on critical issues that impact grower profitability and industry prosperity.

The Production and Postharvest Research Program, supported by the California Walnut Board (CWB), promotes research aimed at lowering costs, increasing efficiencies and allowing the California walnut industry to thrive long term. Importantly, it is grounded in the realities growers face every day. Through the guidance of a committee of growers and handlers, research projects with clear pathways to adoption and those that provide meaningful results are carefully and strategically monitored.

In August, longtime Director of Research Joe Grant is retiring, and with his retirement around the corner, it is a good opportunity to reflect on the accomplishments of the research program in recent years and be excited about the evolving role of production and postharvest research in the future.

Production Research Takes Aim at Challenges
Any grower knows that kernel mold can be a costly and frustrating issue, but industry-supported research has identified the principal fungi responsible for the mold. The development and validation of BUDMON (bud monitoring) and SPURMON (spur monitoring) sampling and diagnostic protocols allow growers to assess the presence or absence of fungi and make informed, risk-based fungicide decisions. The research also established clear guidelines for fungicide applications at bloom and for targeted preharvest applications, further reducing kernel mold risk and directly protecting crop quality and marketability.

Walnut blight also remains a persistent and evolving threat, and research has focused on keeping growers ahead of regulatory and resistance challenges by reducing reliance on older chemistries, lowering overall copper use and slowing the development of copper resistance. Notable wins include research that supported the registration of kasugamycin, now widely used in rotation or combination with copper to manage resistance.

Studies also validated dodine as an effective alternative to mancozeb in copper combination treatments and confirmed oxytetracycline as a promising bactericidal option currently under EPA review.

Production and postharvest research is an important tool to help the industry make progress on critical issues that impact grower profitability and industry prosperity. — Robert Verloop on the value of industry-supported research

Research Delivers Practical Solutions
Production research has also delivered a new pheromone for walnut husk fly (WHF). When added to standard yellow sticky traps, the pheromone significantly increases trap catches and improves early detection. Two commercial suppliers are now offering the lure.

Other production research wins include significant progress using a three-pronged approach against root lesion nematode, combining new chemical, biological and soil-based controls with conventionally bred resistant rootstocks now in grower trials and a first commercial release expected this summer.

Additionally, variety breeding efforts are delivering promising candidates that outperform Chandler in yield potential, kernel color and edible yield while harvesting several weeks earlier. Selections such as Wolfskill and others have shown strong, consistent performance over the past three seasons. Parallel efforts to streamline new variety development are reducing development time and cost, positioning the industry to respond faster to future market and production demands.

Postharvest Research Addresses Efficiency and Quality
Postharvest research efforts are also providing practical solutions for the California walnut industry and addressing efficiency challenges, quality and global market integrity.

Rising energy costs for drying machinery in walnut hulling plants are a substantial input cost, but research has delivered new in-bin sampling and rapid moisture measurement tools that dramatically improve how walnut drying is managed at commercial hullers. Using near-infrared technology to monitor walnut drying, researchers cut moisture testing time from 24 hours to just three hours, laying the groundwork for faster, more energy-efficient drying systems that can help rein in rising costs.

To maintain the premium California quality standard, research has pinpointed the biological mechanism behind walnut kernel darkening, showing that stress triggers naturally occurring compounds in the pellicle to form brown pigments that reduce kernel grade and value. This breakthrough gives the industry a scientific roadmap for developing cultivars and management strategies that help growers produce a crop of lighter-colored kernels and ultimately achieve a higher price point on their harvest.

Protecting Quality and Market Integrity
Postharvest research is also prioritizing origin verification for California walnuts. Walnuts are grown in various countries, and as product origin information becomes more important to consumers, new techniques to differentiate walnut geographical authenticity are needed.

Efforts led by Oritain support a new, commercially ready walnut origin verification system that now allows California walnuts to be authenticated using a unique composition fingerprint. This tool strengthens traceability, prevents misrepresentation and helps protect the premium reputation of California walnuts in the global marketplace.

Looking Ahead
The research program has demonstrated strong progress to date, but like everything else we do, we strive for continuous improvement.

Under new Director of Research and Technical Affairs Dr. Saarah Kuzay, we are moving the Production and Postharvest Research Program toward a coordinated, outcome-driven model designed to ensure industry-supported research meets the most pressing challenges and opportunities. The program will also place emphasis on translating research into real-world applications by identifying promising results, testing them with growers and handlers, supporting adoption and communicating with the industry to confirm solutions are working.

Simultaneously, the program will rebalance long-term production and postharvest solutions with more immediate ones, prioritizing quality, delaying or preventing the onset of rancidity, developing new uses for byproducts and driving market innovation while still supporting integrated pest management, orchard systems and sustainable farming practices. We will also encourage research from a broader pool of research partners, including in-state and out-of-state universities, agencies and private industry.

As the program undergoes this shift, several efforts remain ongoing. Continued testing of biological and organically approved options in walnut blight research aims to broaden future control strategies. Walnut husk fly work will focus on evaluating the addition of pheromones to baited traps. Ongoing research also continues to validate high-performing variety selections and the development of genetically engineered root-lesion-nematode-resistant rootstocks, reducing the need for traditional chemical treatments.

As we look ahead, continued collaboration is needed to deliver science-based tools and insights that enable growers and handlers to make more informed decisions while helping California walnuts remain competitive in a global marketplace, and we cannot do it alone. We encourage you to share your challenges with us so we can work together to ensure research meets industry needs, supports a thriving industry for decades to come and focuses on delivering high-quality, great-tasting, craveable and nutritious California walnuts.

Publisher’s Take

The Big Picture: What to do Next

1. Research is delivering practical returns
New tools and recommendations are helping growers lower costs, improve efficiency and protect crop quality.

2. Kernel mold management has improved
BUDMON and SPURMON protocols help growers make more informed fungicide decisions and reduce risk.

3. Walnut blight options continue to expand

Research has supported new management tools, including kasugamycin and other alternatives to traditional chemistries.

4. New varieties and rootstocks are on the horizon

Breeding programs are producing selections with improved yield, quality and harvest timing.

5. Postharvest innovation is reducing costs and protecting markets

Advances in drying technology, kernel quality research and origin verification are helping maintain California walnuts’ competitive advantage.