Soilborne pests and weeds continue to pose significant challenges for nursery growers and gardeners seeking sustainable management solutions. To demonstrate practical, non-chemical approaches for addressing these issues, the University of California Cooperative Extension (UCCE) Fresno County, in collaboration with the Fresno County Master Gardener Program, conducted a soil disinfestation demonstration during the summer season at the Garden of the Sun in Fresno.

The project compared two environmentally friendly methods- Anaerobic Soil Disinfestation (ASD) and soil solarization for their effectiveness in suppressing weeds and plant-parasitic nematodes under Central Valley conditions. The demonstration aimed to evaluate the potential of these treatments as accessible, low-cost options for improving soil health in small-scale or nursery production systems.

Demonstration Design and Implementation

Two adjacent plots were established and treated for a duration of 50 days. The ASD treatment involved incorporating rice bran into the soil as a carbon source, followed by irrigation and sealing the plot with clear plastic to induce anaerobic conditions. The solarization treatment utilized no organic amendments, relying solely on water and a clear plastic cover to trap solar heat and elevate soil temperatures.

Soil moisture and temperature were monitored using a ZL6 data logger equipped with TEROS 12 soil sensors. Soil water content was maintained at 0.171 m³/m³, and temperatures in both treatments averaged 40–41°C (104–106°F) throughout the treatment period. These conditions are known to inhibit many soilborne pathogens, nematodes, and weed seeds.

Baseline and Post-Treatment Assessments

Prior to treatment, both plots were infested with several common weed species including spotted spurge (Euphorbia maculata), burning nettle (Urtica urens), cheeseweed (Malva parviflora), carpetweed (Mollugo verticillata), nutsedge (Cyperus spp.), and swinecress (Coronopus didymus).

Pre-treatment soil samples were also analyzed for nematode populations: The ASD plot contained 10 Ring nematodes (Mesocriconema xenoplax) per 250 cc of soil. The solarization plot contained 6 Stubby Root nematodes (Paratrichodorus spp.) in the same volume.

Following 50 days of treatment, post-treatment sampling revealed no weed germination and no detectable nematode presence in either plot. Both ASD and solarization produced comparable results in suppressing weeds and nematodes under the experimental conditions.

Implications for Nursery Growers

This demonstration reinforces the effectiveness of ASD and solarization as viable soil disinfestation methods for growers seeking to minimize chemical inputs while maintaining soil productivity. ASD offers flexibility through the use of locally available organic amendments such as rice bran or almond hulls. The microbial activity generated under anaerobic conditions helps degrade organic matter and suppress soilborne pests. Solarization remains a straightforward, cost-effective method that can achieve strong results when soil moisture and plastic coverage are properly managed during the warmest months.

Both methods rely on maintaining consistent soil moisture and ensuring an airtight seal of the plastic cover to achieve uniform heating and, for ASD, sustained anaerobic conditions.

Conclusion

The results from the Garden of the Sun demonstration indicate that both anaerobic soil disinfestation and solarization can effectively suppress weeds and plant-parasitic nematodes within 50 days. These findings highlight the potential of these non-chemical soil management practices to support sustainable production in nursery and garden settings. UCCE Fresno County will continue to collaborate with the Master Gardener Program to promote and evaluate practical soil health practices that enhance productivity and environmental stewardship.