It's time to become water-smart

As more growers look to install closed loop irrigation systems, there is a need for treatment systems specifically tailored to handle horticulture issues related to biofilm and disease control.

By David Kuack

The intense drought in California and continuing drought in Texas along with their impact on the rising cost of food are making government officials and the public painfully aware of the importance of having and maintaining a reliable water supply. USA Today reports that California produces nearly one-fifth of the United States’ entire agricultural output. Should the state’s water woes continue the newspaper said farmers and distributors may soon have to start looking for alternative locations to grow or buy their crops.

The outlook released by the National Drought Mitigation Center (http://drought.unl.edu) indicates that drought will also likely develop in portions of Arizona, Texas, and California where there currently is no drought. The center indicated California remains on track for another year of historic drought that has resulted in curbed water supplies and a request from Governor Jerry Brown for a 20 percent reduction in water use. In addition to reducing the state’s agricultural production, the center said the drought is expected to drive up unemployment locally and food prices nationally.

Focus on water conservation

University of Connecticut assistant professor and greenhouse specialist Rosa Raudales said ornamental growers along the West Coast are well aware that water issues are only going to intensify and are taking action.

“Water quality and availability are going to continue to become bigger issues,” Raudales said. “There are some regulations at the state level, like on the West Coast, and others more localized at the county level in other states. However, it is expected that tougher regulations on water management will arise and affect agriculture. Many ornamental growers are trying to stay ahead of the regulations and are installing closed irrigation systems.”

Pacific Plug & Liner in Watsonville, Calif., recently installed a
water reclamation system to collect and treat irrigation runoff
from its outdoor field production.
Photo courtesy of Pacific, Plug & Liner

EPA released the report “The Importance of Water to the U.S. Economy” in November 2013.
“In this report, EPA discusses the value of water and the interconnectivity of water bodies,” Raudales said. “What this report indicates is that the true dollar value of water has long been underestimated.

“In addition, the report discusses the importance of how all water sources are connected as a means to protect drinking water sources. The implication for growers could be that the cost of purchasing water could increase. Also, because water sources are interconnected, there could be less freedom for how growers manage their water sources and the runoff on their property. Long term, U.S. greenhouse operations could be forced to install closed loop irrigation systems, like the growers in some European countries.”

Increased emphasis on water quality

Raudales said as more growers look to recycle their water the quality of that water is going to become a bigger issue. She said growers who have installed closed loop systems are filtering the water and then treating it with chlorination or some other chemical.


Raudales recently surveyed 43 young plant growers nationally and inquired as to the type of water treatment system they were using. She found among these growers s that the systems most commonly used were copper ionization, activated peroxygens and chlorine.

“Based on my discussion with growers, plant disease is an issue when producing a very susceptible crop,” she said. “Although disease is not frequently observed, there is a still a risk of losing plants. Growers manage the disease risk caused by waterborne pathogens by using a combination of continuous low dose sanitizers in the irrigation system and good watering practices to avoid overwatering.”

Raudales said the most common water-borne pathogen found in greenhouses is usually Pythium. She said in nurseries, Phytophthora is the most common water-borne pathogen.

“Pythium and Phytophthora have swimming life stages called zoospores that allow them to move freely in water,” she said. “In contrast, the disease pathogens Fusarium, Thielaviopsis and Rhizoctonia move in water along with debris such as peat, leaves and dead roots. Growers should use filtration systems to remove debris to reduce the risk of these pathogens.”

Battling biofilm

Raudales said biofilm is a common problem in the horticulture industry regardless of the crop or type of operation.

“Biofilm, commonly referred to as “slime,” is a matrix of multiple microorganisms with extracellular polymeric substances that build up in layers in water pipes and emitters,” she said. “It is a very complex structure built mainly by bacteria, but it can also harbor other types of microorganisms.”

Raudales said biofilm will build up even in clear water with no soluble fertilizers or turbidity.

“Microbes that begin to form biofilm are relatively stagnant until their population has increased to a certain level,” she said. “Once that level is reached, there is a “team effort” and the microbes release extracellular polymeric substances that makes the biofilm look slimy. Every time water flows through a pipe, even if it is clean, more microbes are added to the biofilm.”

Raudales said there are different types of biofilms depending on the organisms and the metals in the water. A common one is created by iron bacteria that results in an orange-colored biofilm. There are also dark green and light-colored biofilms. She said there is a lot of diversity with biofilms, which makes treatment more complicated.

Raudales said biofilm is very costly for growers to manage because it involves labor to monitor, replace and clean clogged pipes and emitters.

2-inch PVC water pipe showing:

Top: new pipe.

Middle: clear water line showing biofilm formation.

 Bottom: constant liquid feed line showing algae and biofilm. 

Photo courtesy of Konjoian's Floriculture Education Services

“One of the main issues with biofilm is uneven water delivery to the plants because of clogged irrigation emitters,” she said. “Growers may be unaware of this uneven watering until they start to see wilted plants. Managing biofilm may involve manually cleaning and replacing emitters.”

Raudales said there are chemicals, including chlorine dioxide and activated peroxygens, that can reduce the number of microorganisms in the water to prevent or reduce biofilm buildup.

“The issue that growers face is high concentrations of sanitizers can also be phytotoxic to plants,” she said. “Growers should consider multiple levels of control. Chemicals are one part, but growers should also try to remove as much debris from the water as possible through filtration.

“Using chlorine is an expensive technology, but it is also one of the technologies for which most of the research has been conducted. Some growers avoid using chlorine because of the risk of phytotoxicity, especially in the overhead irrigation of young plants.”

Raudales said growers who are considering chlorinating their water, should also think about dechlorinating their water to reduce the risk of phytotoxicity. She said most growers are not dechlorinating their water.

“If growers are putting a chemical in their water, they should also be thinking about removing the chemical right before they reuse the water on their plants,” she said. “The chemicals that can be used to kill the biofilm microorganisms may also be phytotoxic to the plants. More research is needed in this field.”

Raudales said an alternative treatment would be to shock the irrigation system with a higher chemical concentration. This treatment has to be done when the plants aren’t present. She said a higher dose can remove the biofilm from the irrigation system, including the emitters.

Biofilm is not unique to horticulture and Raudales said growers can learn about its treatment from other industries.

“There is a lot that we can learn from factories,” she said. “These facilities have very long piping systems and they treat to control biofilm a lot. The difference is these other industries are able to use stronger chemicals.”

Raudales said when water-soluble fertilizer is injected into an irrigation system, algae will grow.

“As long as there are nutrients in the water, you will see algae,” she said. “What controls biofilm does not necessarily kill algae. They are very different organisms. While biofilm builds up in layers, algae are a simple, single layer. Water to which water-soluble fertilizers are injected adds a complexity to the water chemistry as well.”

Traditionally algae have been controlled with copper-based products. Raudales said it is unknown if copper-based products are effective for controlling biofilm.

Designing a better treatment system

Raudales said there is a business opportunity for companies to specialize in the design of water treatment systems specifically for greenhouse operations.

“Many water treatment companies are providing a product or technology,” she said. “Only a few of them are talking about the design.”

Raudales plans to continue working with University of Florida professor Paul Fisher, who was her doctoral advisor, on water treatment design.

“In many cases, water treatment systems have to adapt to pre-installed irrigation systems and available greenhouse space,” she said. “The grower who is starting from scratch with a new facility has the advantage of creating a comprehensive design with multiple barriers to reduce risks of contamination and phytotoxicity.

For more: Rosa Raudales, University of Connecticut, Department of Plant Science and Landscape Architecture; (860) 486-6043; rosa.raudales@uconn.edu.

David Kuack is a freelance technical writer in Fort Worth, Texas; dkuack@gmail.com.

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