Get to know your greenhouse water

Editor's note: Before you read the article below, be sure to check out the Irrigation Technology Annual Report, which features a closer look at how greenhouse irrigation automation is advancing, even with hurdles.

In a recent series on OnFloriculture.com, Dr. Sarah Jandricic, a Greenhouse Floriculture IPM Specialist, and Dr. Chevonne Dayboll, Greenhouse Floriculture Specialist, with the Ontario Ministry of Agriculture, Food and Rural Affairs, offers critical advice for growers on testing and treating their water supply. Here are just a few insights they offer.

The Do's and Don'ts of Sampling Your Water

You can find several tips on how to monitor, interpret, and solve chemical issues for water used to irrigate greenhouses and nurseries in a YouTube video produced by Dr. Paul Fisher from the University of Florida's Institute of Food and Agricultural Sciences. The video is part of a series called "Five Tips for Horticulture" featured on the university's Greenhouse Training Online channel.

Regarding when, where, and how to sample, Jandricic and Dayboll recommend you consider the following Do's.

• DO monitor at frequencies that relate to the level of risk. These include different points in the production cycle (especially before a new crop goes in); when there are changes in source water quality occur (e.g., switching from roof water to water stored in a cistern), when sensitive crops are present (based on crop type and/or stage; this is why knowing your crop's susceptibility to diseases before you plant is so important); and when labor is available.
• DO sample from all sources of water and from various points along your irrigation system. This can reveal potential sources of contamination and gives you a picture of how pathogens are spreading throughout your farm. Testing along your irrigation system can also reveal issues with water pressure and distribution that may be causing wet or dry spots in the crop, which can also lead to disease problems. Try to sample from locations that are close to where the water enters the production area (e.g., in the first few rows or benches) and those that are near the end of the line to get a better idea of the problems you might be facing.
• DO sample recirculating water before and after water treatment. This tells you if your chosen water treatment strategy is actually working like it's supposed to. Never assume that it's functioning properly. All systems need maintenance and some need proper levels of active ingredient(s) to work, which can change frequently depending on the amount of organic matter in the system. Be safe, and follow a regular testing schedule to maintain your investment.
• DO follow the guidelines suggested by your chosen lab. Many labs have specific guidelines for collecting water samples as well as general shipping/handling guidelines. Make sure to read over these thoroughly before collecting and sending samples. In a pinch, you can use disposable water bottles to collect samples, but ensure they are rinsed with your source water well before taking a sample. Never use vessels that were used for another purpose (e.g., scoops for mixing fertilizer) to grab samples, as they may leave residue in your sample that can affect your results.
• DO have a consultant or specialist help you interpret the results of any tests. They can help you figure out which pathogens are pests of concern, and what to do about them.

What not to do can be as important as what to do. Consider these don'ts and make sure to think of others that may apply to your own farm.

• DON'T leave sampling until the last minute. Sampling should be a proactive activity, not a reactive one. But if you're like many of us, a lack of time and too much on your plate can mean that your water samples are taken after crops have gone in, or you spot something that isn't right. Schedule regular water sampling into your calendar and make sure it gets done ahead of sensitive crop cycles or your big spring season.
• DON'T be afraid to send in several samples at once, despite the cost. Whether you like to do a more thorough check of your irrigation systems twice a year, or you are facing a problem and don't know where to start, more samples can help you pinpoint a problem more accurately in the greenhouse, saving you time and headaches.
• DON'T forget to factor in costs of regular sampling into your pest management costs. DNA tests that sample for potential pathogens down to species cost around $250 (Canadian) per sample. This is a drop in the bucket compared to the crop losses you might see due to pathogens in recirculating water, so make room for them in your pest control budget.

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Source: Greenhouse Grower