DECEMBER 2017 • COUNTRY LIFE IN BC


Cleaner water promises greener greenhouses There are no shortcuts when it comes to water and plant health


----by PETER MITHAM ABBOTSFORD –


Greenhouse water quality is more than a question of measuring up to standards; it should be about boosting plant health and performance. But growers who focus just


on keeping water clean without looking at the rest of their operations risk compromising plant health and long-term greenhouse performance, says Al Zylstra, a Seattle-based consultant who oversees the water division of Dramm Corp. “It’s really important when


you’re looking at water treatment to start out asking what are my objectives? What do I need to accomplish?” Zylstra says.


Sometimes it about meeting compliance targets, for others it’s about preventing fusarium outbreaks. Others want to be good neighbours or reduce run-off. Still others want to maximize plant health and performance. According to Zylstra, the last group of growers has the best chance of seeing a payback on its efforts. “It actually pays the bills. … That’s the one that has


the ability to put some money in our jeans,” he says. “But it’s the one that is paid the least attention to.” Biofilm is the key enemy of plant health in


greenhouse irrigation systems. US Centers for Disease Control estimate that more than 99% of the bacteria in water systems reside in biofilm attached to pipe surfaces. Zylstra’s experience suggests that biofilm is in turn the source of 70% of all water- borne pathogens in greenhouses, and the tenacious films accumulate faster than experts once thought. “We thought for a long time that a biofilm was


something that took years and years and years to develop and we didn’t need to worry about it,” Zylstra says. “Well, that’s not the truth. … [This] has been the untold story of water treatment until the past 15 years or so.” Zylstra likens what growers are doing to putting


clean food on a dirty plate. Since water is constantly flowing through the pipes, there’s no such thing as the “five-second rule” people often joke about in grabbing a scrap of food off the ground at a picnic. Biofilm is no picnic. “It’s probably causing all of your problems that


you don’t know about,” Zylstra says. “Any pathogen that’s ever lived in your greenhouse? Had a case of fusarium 20 years ago and got rid of it? It’s in your piping system, I guarantee it. You’ll find it if you do a DNA analysis. It’s just lurking in one of those hiding places looking to get out.” Worse, because the pathogens have managed to


find safe harbour and persist in the pipes, they’ll have acquired resistance to anything that was trying to eradicate them. This means they’re likely to be hundreds of times more resistant than regular bacteria. “Once it gets into the biofilm, it gets really, really tough to kill,” Zylstra told growers. “So how do we get rid of it?” Pushing clean water


FILE PHOTO


through the lines isn’t the answer, nor is using a chlorine solution because it sanitizes but doesn’t kill the matrix that supports the biofilm, which begins forming within hours. Copper ionization also fails because it doesn’t have the horsepower required to disrupt and destroy the matrix. “Only three things work,”


Zylstra says. “Ozone will kill a biofilm matrix on contact; chlorine dioxide will kill a biofilm matrix, but it won’t do it on contact. … Activated hydrogen peroxide will do the job.” Moreover, like a regiment of antibiotics, the


treatment process has to be continuous to ensure the complete and final eradication of the film. Just as biofilm can carry pathogens upstream, a


problem upstream can make it way downstream. This means the entire irrigation infrastructure needs to be addressed in a holistic sanitation strategy. “You’ve got to look at everything from the water


source, where it’s coming from to start with, all the way through to the dripper that puts the water in that plant and what happens to that water when it goes into the root system of that plant,” Zylstra says. “You can’t miss anything in between.”


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