HOLTVILLE — A local three-year research project to determine whether drip-irrigation systems can help reduce the incidences of downy mildew in organic spinach is showing “promising results.”
The groundbreaking study is being conducted at the University of California Cooperative Extension and led by Aliasghar Montazar, UCCE irrigation and water management adviser.
Downy mildew, a plant disease, is a major concern among spinach growers and often results from the use of sprinkler irrigation, which is used exclusively in spinach production, and which deposits water on the crop’s leaves and can lead to downy mildew if not managed properly, Montazar said.
In contrast, driplines deliver water directly to the crop’s roots, eliminating any contact that irrigation water may have with the spinach leaves, and thereby helping reduce instances of downy mildew, he said.
“This is the first time we’ve done this in California — in the world actually,” Montazar said as he excitedly gestured toward the UCCE’s experimental beds of spinach on Feb. 12.
The three-year study is now in its final stages. Once concluded, Montazar said he plans to publish the findings in UCCE’s and other ag-related publications and make a presentation at the annual California Leafy Greens Research Board state conference in March.
“Promising” Results
The origins of the research project date back a few years to a meeting Montazar had with members of the California Leafy Greens Research Board, which had expressed concerns to him about spinach downy mildew causing substantial losses in the crop’s statewide yields.
He suggested to the board that drip irrigation could be used in place of sprinklers to potentially reduce instances of the plant disease, which is also a food safety concern for growers.
“They asked me if I had any idea to resolve this issue and I came up with this idea,” said Montazar, who has spent more than 18 years researching irrigation management, engineering, and structures and has been assigned to the local UCCE since 2017.
So far, his experimentation has demonstrated that downy mildew disease was four to five times less prevalent in the experimental drip irrigation-fed organic spinach beds compared to the adjacent beds that had used sprinkler irrigation.
“It’s pretty significant,” he said.
Locally, about 8,000 to 10,000 acres of spinach is grown annually, all of it using sprinkler irrigation, Montazar said. Its relatively brief growing and harvesting season is in the fall and winter.
His research was conducted solely on organic spinach, which does not use synthetic fertilizers, pesticides, or herbicides, and which presented additional challenges because of its sensitivity, he said.
Nonetheless, a non-organic spinach grower in Winterhaven has already adopted the use of driplines in their fields and has reported a savings of about $150 per acre in fertilizer, Montazar said. He further explained that drip irrigation has a proven track record of conserving water and fertilizer in comparison to sprinklers.
“The results we got from his field is much, much better,” he said, referring to the grower’s savings of about $300 per acre in water and fertilizer expenses.
Additionally, Montazar was successfully able to germinate, for the first time, the industry-standard 80-inch-wide spinach beds with drip irrigation, as opposed to the traditional use of sprinklers.
Though preliminary experiments revealed that the dripline-irrigated spinach beds produced 1.5 percent less seedlings, the difference was not that significant and could be addressed easily enough with a corresponding increase in the amount of seeds planted.
“It’s promising,” he said, referring to the study’s overall results related to plant disease control, germination, and fertilizer reduction. “There are a lot of benefits.”
Different Experimental Configurations
To find the optimal conditions for dripline irrigation, Montazar and his collaborators experimented with a variety of configurations over the course of the three-year study, which began in the winter of 2018-2019.
After the initial planting season, they eventually abandoned the use of surface driplines, which produced less crop yield than the subsurface driplines, and which were blown astray by strong winds despite the use of stakes.
Researchers also varied the number of driplines that were buried in the raised spinach beds. Beds with four subsurface driplines produced yields 12 percent more than those with three subsurface driplines, while the sprinkler treatment resulted in yields 13 percent higher than the beds with four driplines, Montazar wrote in a local UCCE Ag Brief article in January 2019.
“However, we believe that this yield gap can reduce through optimal drip irrigation system design and better irrigation and nutrient management,” he wrote.
The research is scheduled to continue in the Salinas Valley later this year, where its sandy soil conditions differ from the silty clay soil found in the Valley, Montazar said. The sandy conditions to the north may likely require the use of four subsurface driplines to achieve optimal irrigation conditions, he said.
California leads the nation in the production of spinach, with most of it grown in the Central Valley and in the low desert of the Imperial and Coachella valleys.
Locally, spinach was listed last in the county’s top 10 ranking of commodities’ overall gross value in the 2019 Agricultural Crop & Livestock Report. That year, some 8,128 acres of spinach generated about $57.9 million in gross value, the report stated.
Encouragement for the Industry
Though he admits additional research and experimentation is needed to further optimize his study’s findings, Montazar said the preliminary results should be encouraging to spinach growers, if the initial industry feedback he has gotten is any indication.
“The California Leafy Greens Research Board is very excited about the results,” he said.
The California Leafy Greens Research Board funded Montazar’s spinach research, and for the past 10 years has contributed about $600,000 annually toward similar research efforts across the state, its website stated.
Even so, the transition to drip irrigation may prove challenging for some spinach growers because of the capital and labor initially required to purchase and install the subsurface driplines, Montazar said.
That’s why research such as his is crucial, he said. It helps foster additional collaborative opportunities between academia, the industry, and government, which can provide financial incentives for growers that pursue additional water, pesticide, and fertilizer conservation.
Toward that end, Montazar continues to work with dozens of commercial growers in Imperial and Riverside counties, where about 90 percent of his research into water conservation and irrigation management is conducted.
A native of Iran and the son of a farmer, Montazar said he was motivated to study irrigation by the childhood memories of a two-year drought that took its toll on desert farmers such as his father.
“When we want to encourage growers to adopt a practice, we need to know how valuable that technology is,” Montazar said. “We need to bring that data to the table.”
