by Courtney Llewellyn
A lot of attention is paid today to ensuring surfaces are safe and clean for humans – but what about the surfaces plants touch? They’re susceptible to a variety of diseases as well.
Rosa E. Raudales, assistant professor of horticulture and greenhouse Extension specialist at the University of Connecticut, speaks somewhat passionately about this topic, which she covered in a recent presentation during Cultivate’20. And when it comes to surface sanitation in greenhouses, it’s important to ask “Which surfaces?”
“When I go into greenhouses, I’m not like everybody else. I don’t look at the plants. I look at the different surfaces and what’s going on on them,” Raudales said. “Surfaces are very diverse, and microorganisms are omnipresent in your operation” – they can grow everywhere.
When putting together an indoor growing facility, Raudales said people need to consider the different physical properties of different surfaces, from wood to concrete to PVC to stainless steel. The three major properties she said to focus on are hydrophobicity (the ability to repel water), porosity (surface roughness) and surface waviness. They will largely tell you how easy something is to clean – or how likely it may be to harbor unwanted microorganisms.
“Also think about access to surfaces – how easy it is to get to areas that need cleaning,” Raudales continued. “I know it’s hard for growers to not use space, especially in springtime, but you need to be able to clean all spaces.”
Sanitation plans are a must, whether in an existing structure or planning to build anew. Raudales suggested having a sanitation plan in place before you break ground. Growers will also need to consider their cleaning needs when purchasing new equipment or designing a building. “Cleaning well requires labor,” she said. “You might buy equipment that might be cheaper, but think about the cost of labor to clean things as well.”
Targets for sanitation on tools, tabletops, floors, walls and more are organic debris, plant pathogens (as well as human pathogens) and algae/biofilm. Raudales said if a particular pathogen seems to be causing trouble to keep that target in mind, but you should clean and sanitize as if all targets (pathogens) are present. It’s a risk management strategy.
Deal with potential plant pathogens the same way you would human pathogens – clean first, sanitize second. Cleaning means removing debris, which includes plants, growing substrates and weeds. Then, surfaces can be washed with detergents, which Raudales said are “pretty effective at removing organic films and oils.”
One relatively simple way to disinfect after cleaning is to “cook” the greenhouse with high temperatures, but that can only occur when its empty, usually at the end of the season. A method that can be used throughout the growing season is to apply a disinfectant. “Our goal is to reduce microbial inoculum, which is why all the previous steps are so important,” Raudales said.
The dose of the disinfectant is critical. Defined, a dose is the concentration of the disinfectant tied to its contact time. If the recommended dose seems too harsh to place near plants, you can reduce its concentration, but you will need to increase the time the product remains wet for it to remain effective.
Disinfectant products can be liquids, combinations with organic acids or solids. Some of the most commonly used examples employ hydrogen dioxide/peroxide, quaternary ammonium compounds (QACs), chlorine, ethyl or isopropyl alcohol and phenolic compounds. While all are effective on different inoculums, users need to remain mindful of their potential toxicity.
The most important thing, Raudales said, is to “start clean, stay clean.”