How do I know if I am adding enough chlorine into my irrigation water to control plant pathogens?

Measuring chlorine

Select a meter that will measure free and total chlorine.

Decide on the target chlorine dose. To check for research on dose response of chlorine or other sanitizers for a range of pathogens, use our Waterborne Solutions tool under Grower Tools on this website. For example, 2 ppm of free chlorine is a commonly applied dose which can control Pythium and Phytophthora zoospores.

You need a reliable meter with reagents to test for both total and free chlorine - check common brands for water quality monitoring such as Hach, Hanna, or Pulse Instruments. Although free chlorine is the most effective sanitizing form of chlorine, it is also important to measure total chlorine to avoid phytotoxicity (beware of ever applying more than 5 ppm total chlorine or 2 ppm of free chlorine).

Invest in a reliable inline dosage measurement and control system. You should have inline sensors to measure pH and oxidation-reduction potential (ORP), and possibly ppm of chlorine. Most phytotoxicity problems result from faulty equipment or calculations - don't fix one problem (pathogens) while creating another (phytotoxicity).

Check that the dilutor or injector is working correctly. Calculate how much chemical is being applied for a given volume of water. You can also use our ppm to Recipe tool in, under Tools, to help calculate the dose.

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