UC ANR research on drip irrigation shows potential to reduce downy mildew incidence while improving water quality and resource-use efficiency, contributing to increased water-use efficiency and improved food safety. 

The Issue

Spinach is a leafy green quick-maturing, cool-season vegetable crop. Downy mildew on spinach is a widespread and very destructive disease in California. It is the most significant disease in spinach production, causing  crop losses in all areas where spinach is produced. Most conventional and organic spinach fields are irrigated by solid-set or hand-move sprinklers. However, overhead irrigation may contribute to the speed and severity of downy mildew epidemics within a field when other conditions such as temperature are favorable. It is postulated that new irrigation management techniques and practices in spinach production may have a significant economic impact to the leafy greens industry through the control of downy mildew.

Commercial conventional spinach field

How UC Delivers

The main objective of this study was to explore the viability of adopting drip irrigation for organic and conventional spinach production. Field experiments were conducted at the UC Desert Research and Extension Center and three commercial fields in the low desert of California over four crop seasons (2018-2021). Several treatments and  comprehensive data collection were carried out to optimize drip system design, irrigation and nitrogen management strategies, planting method, and evaluating the effects of drip on plant growth and downy mildew incidence, and seed germination by drip irrigation.

The results of this multi-year study demonstrated that drip irrigation has the potential for producing profitable spinach in the California crop production system. No significant yield difference was observed among sprinkler treatments and most drip treatments in the 2021 trial. An overall effect of the irrigation system on downy mildew was observed, in which downy mildew incidence was two-to-five times lower in plots irrigated by drip when compared to sprinklers. The likely mechanism for reducing downy mildew incidence is the reduction in leaf wetness resulting from drip irrigation. Leaf wetness is a critical factor for infection and sporulation by the downy mildew pathogen.

Organic spinach trial at UC Desert REC

The Impact

The findings of the aforementioned study show that adopting drip irrigation for high-density spinach plantings can reduce incidence of downy mildew and related food safety risks and crop loss. As a result of participating in research trials, a cooperative grower reported a considerable cost reduction of $300 per acre due to less/no water treatment applications for downy mildew control and food safety issues in conventional spinach under drip irrigation. The findings of this study show that adopting drip irrigation for high-density spinach plantings can be a solution to reduce food safety risks and losses from downy mildew, conserve water and fertilizer, and reduce greenhouse gas emissions. A lower energy cost of $200 per acre is estimated for spinach producing under drip irrigation.

Several factors influence appropriate drip irrigation management in spinach including system design, soil characteristics, and environmental conditions. Drip irrigation offers the potential for precise water management, as well as the ideal vehicle to deliver nutrients in a timely and efficient manner. However, achieving high water- and nutrient-use efficiency, while maximizing crop productivity requires intensive and proper management, particularly in organic baby spinach. The knowledge-based information and findings of this study have been shared with growers and stakeholders through several media interviews, presentations in workshops/webinars, and extension and peer-review publications, contributing to UC ANR's public values of resource conservation and safe, sufficient food for all. The following links are some of the publications associated with this study in Western Farm Press, the Desert of Review, the Holtville Tribune, California Ag Today Radio, Vegetables West, California Organic Farmer, Journal of Agriculture, Agricultural Briefs, and UC ANR Knowledge Stream:

The Holtville Tribune - May 2021

Vegetables West - April 2021

California Ag Today Radio - March 2021

Western Farm Press - February 2021

Journal of Agriculture - August 2019

California Organic Farmer - August 2019

UC ANR Knowledge Stream - August 2019

UC ANR Agricultural Briefs - June 2019

UC ANR Agricultural Briefs - February 2019