Sanitation Tips for Greenhouse Vegetable Growers

Tomatoes in a Greenhouse Sanitation Dramm

One of the best pieces of advice for greenhouse vegetable operations is to start clean and stay clean. The row shown above has no debris to attract and feed pests. Photo: DRAMM

Indoor vegetable growers know the challenge of sanitation. Best practices differ from ornamental horticulture, in some ways, because the pathogens are different, says Al Zylstra, Manager, Water Segment at DRAMM. Vegetable growers should know what pathogens are the most critical to control specific to their crop. However, regardless of the crop being grown, the importance of high-level sanitation and pest management is the same and critical to success.

To properly manage pathogens in irrigation water, Zylstra says growers should pay attention to the method of pathogen control, such as ozone, chlorine dioxide, or UV. He names three best practices for indoor vegetable growers — learn the chemistry of sanitizing agents, start clean and stay clean, and manage plant stress.

Know the Chemistry

It is essential for growers to understand the chemistry behind their sanitizing agents, whether it’s UV, ozone, chlorine dioxide, or another option. Do the research to know the mode of action of the sanitizing agent and the CT values (concentration of the sanitizer required, and the contact time of the sanitizer with the water/pathogenic microbes).

“We see a lot of misapplication of the chemistry because of a failure to understand exactly how that chemistry reacts, whether that’s understanding the length of contact time required, where the sanitizer needs to be applied/injected, the requirements for mode of action to be effective, such as concentration, pH level, water temperature, electrical conductivity (EC) level, and more,” says Zylstra.

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Some sanitizing agents are more effective or lose their effectiveness at a particular pH.

“It always requires a multi-disciplined approach. It requires correct design of how and where the equipment is implemented, what sanitizer is being used, and the required pre- and post-treatment filtration levels to achieve optimum efficacy,” Zylstra says. “It also requires correctly sized pumps to deliver optimum water pressure for the correct operation of each component in a system, required contact time of each targeted pathogen for the specific sanitizer being used, concentration, oxidation capacity, EC effect, water temperature, and mode of action. There is no silver bullet solution.”

When growers make a mistake with sanitizing agents, often it goes unnoticed until a larger problem arises in the future. Zylstra says he deals with biofilm control on a daily basis. In some cases, growers did not realize that a sanitizing agent was not effective against biofilm until a few years later when a significant biofilm problem became apparent. Perhaps a sanitizing agent was misapplied or used at the wrong concentration several years ago. If that goes untreated, many water borne pathogens could be spread every time the water is turned on.

Optimize Sanitation Practices

Growers, whether they are growing flowers or vegetables, face similar sanitation challenges, according to Heidi Lindberg, Greenhouse and Nursery Extension Educator at Michigan State University. However, vegetable growers have sanitation practices that are a step above.

“When visiting growers producing vegetables — whether it be lettuce or vine crops such as cucumbers or tomatoes — the first thing you’ll notice is the increased presence of sanitation. Growers should be using food baths around the facility and clean up greenhouses (first organic matter and then sanitize them between crop cycles),” she says. “Many of the vegetable greenhouses also implement protocols such as hair nets, foot booties, lab coats or uniforms, and gloves. Food production greenhouses must comply with regulations such as Good Agricultural Practices (GAP) audits, and other management practices.”

Some growers have a processing facility in-house, she says, and automation is the easiest way to prevent human-borne illnesses. Lindberg says a trimmer could cut off lettuce. The vegetables are processed or packaged in a food-grade facility, where employees have more extensive sanitation protocols, such as hair nets, gloves, and specific changing areas and washing stations.

Manage Plant Stress

Aside from sanitation practices, Zylstra says managing plant stress is also a key factor in growing healthy plants. A grower could implement all of the best sanitation practices, but if the plants are stressed by factors such as heat, water, or light, they are still a susceptible host to pathogens.

“That’s one of the three legs of the disease triangle — a conducive environment for pathogens to develop, such as temperature, humidity, and air movement. The second one is the presence of a sufficient level of pathogenic microbe able to infect the plant. The third leg is a susceptible host plant that will be attractive to the pest or pathogen to survive and thrive,” Zylstra says.

Automating irrigation reduces the likelihood of overwatering or underwatering plants so they don’t develop wilt. Ensuring that shade curtains are deployed properly and HVAC systems are running smoothly are the “first line of defense” in protecting your crop from pathogens.

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