· Principle component of phosphate fertilizer; usually in the form of ammonium phosphate, potassium phosphate, or calcium phosphate. Plants take up and used phosphate ions (H 2 PO 4or HPO 4 =) for ATP, DNA, photsynthesis, respiration, and other metabolic functions. Phosphate does not have fungicidal properties. Phosphonates as fungicides. Fungicidal properties of phosphonates were .