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TECHNICAL INSIGHT PHOSPHITE
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Phosphite in turfgrass
Phosphite has become an important nutrient in turfgrass over the past decade. Here, we explain its benefits and how and when to use it BY DR JOHN DEMPSEY, TURFGRASS RESEARCHER
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hosphite is a form of phosphorus (P), which is a major plant nutrient vital for optimal growth and development required in amounts second only to nitrogen. As a nutrient source, phosphorus is only available as phosphate. Phosphite is chemically similar to phosphate, as both ions have a central phosphorus atom. With phosphate, the atom is combined with four oxygen atoms (PO43-). With phosphite, however, only three oxygen atoms are combined with the phosphorus atom (PO33-). While one fewer atom of oxygen may seem
inconsequential, the result is significant as phosphite cannot participate in the same plant biochemical reactions as phosphate. Phosphite is derived from phosphorous acid (pH2.2) and if applied to plants is phytotoxic. It is modified prior to use with an alkali salt, originally with aluminium ions, which produced fosetyl-Al, a plant protectant first marketed in the 1980s that was successful in controlling turfgrass diseases such as Pythium. Since the early 2000s, potassium hydroxide has been used to neutralise phosphorous acid. This produces potassium
phosphite, which is the basis of numerous turfgrass products sold to help control disease as biostimulants, nutrient sources and defence activators. HOW EFFECTIVE IS PHOSPHITE? Phosphite's ability to suppress certain diseases is well documented as it has been shown to suppress Dollar Spot, Anthracnose and Fusarium Patch (Microdochium nivale). Numerous field trials in Europe and the US have determined that there were significant M. nivale disease reductions on phosphite-treated trial
plots when compared with untreated controls, and that the addition of phosphite significantly enhanced fungicide efficacy. The means by which phosphite suppresses disease is two-fold. • Directly: Phosphite inhibits fungal growth and reproduction. This slows the infection process allowing the turfgrass time to respond with defences. • Indirectly: Infected turfgrasses produce numerous antimicrobial compounds leading to induction of systemic acquired resistance. Phosphite treatment primes and stimulates these defence
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