Pistachios have become a major area of focus as we expand soil fumigation research into new crop markets. Nearly all U.S. pistachios, about 99%, are grown in California, with production centered in the San Joaquin Valley. The region’s hot, dry climate creates ideal growing conditions, supporting both high yields and consistent quality. This strong regional base has positioned the U.S. as the global leader, producing more than 63% of the world’s pistachios and serving as the top producer and exporter worldwide.

Industry shifts, such as declining walnut production and the maturation of almond acreage, highlight why pistachios have emerged as one of California’s fastest-growing and most valuable crops. Their adaptability and drought tolerance make them particularly well-suited to the Central Valley, where water scarcity remains a constant challenge. This rapid growth creates an important opportunity to explore how soil fumigation can support orchard establishment, early tree development, and long-term yield potential. Just as fumigation has shown proven benefits in walnuts and almonds, evaluating its role in pistachios can help growers optimize productivity in a crop that is increasingly critical to California’s economy, global trade, and agricultural sustainability.

To investigate this, we established two pistachio trials in Fresno County that were soil fumigated in Fall 2022. By Spring 2025, 2.5 years of data had been collected on tree growth and plant-parasitic nematode pressure. At the Firebaugh, CA site, treatments included TELONE™ II by Teleos at 33 GPA + TriClor at 200 lbs/acre, three TriClor rates (150, 200, and 250 lbs/acre) applied as non-tarped deep strip treatments, and an untreated control. Tree growth and nematode populations were evaluated twice annually to measure treatment performance.

Tree Growth Results: Examining tree circumferences from the Firebaugh site, all fumigant treatments promoted stronger growth compared to the untreated control. TriClor at 200 lbs/acre consistently delivered the greatest growth at each time point, resulting in a 12% increase in circumference over untreated trees by Spring 2025. These findings highlight the effectiveness of TriClor, particularly at the 200 lbs/acre rate, in helping young pistachio orchards establish faster and stronger.

Nematode Results: Assessments of plant-parasitic nematode populations from 2023 through 2025 revealed clear treatment effects. Within the trial site, root lesion, spiral, pin, and stunt nematodes were recovered. In Spring 2023, all soil fumigant treatments provided near-complete suppression, while untreated plots showed very high nematode pressure. By Spring 2024, some rebound was observed in TriClor-treated plots, most notably at 150 and 200 lbs/acre, though populations still remained well below untreated levels. TELONE™ II by Teleos at 33 GPA + TriClor 200 lbs/acre delivered the most consistent suppression across both 2024 and 2025, while TriClor continued to provide strong early-season reductions with partial recovery over time. By Spring 2025, untreated orchards again carried the highest nematode pressure, emphasizing the importance of soil fumigation in protecting young trees from root damage and supporting stronger establishment.

Soil fumigation has proven effective in supporting young pistachio orchards. TriClor produced the strongest gains in early tree growth, especially at the 200 lbs/acre rate, while the TELONE™ II by Teleos 33 GPA + TriClor 200 lbs/acre strip treatment provided the most reliable long-term suppression of plant-parasitic nematodes. Together, these results highlight how soil fumigation protects root systems, enhances orchard establishment, and contributes to the long-term success of California’s pistachio industry.

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