CONTROLLING POWDERY MILDEW CAUSED BY SPHAEROTHECA-FULIGINEA IN CUCUMBER BY FOLIAR SPRAYS OF PHOSPHATE AND POTASSIUM-SALTS

Powdery mildew in greenhouse-grown cucumber (Cucumis sativus L.), caus ed by Sphaerotheca fuliginea (Schlecht.:Fr.) Pollacci, was significant ly controlled by a foliar spray pre-inoculation treatment of 20 mM aqu eous solutions of either monopotassium phosphate or potassium nitrate, or a 0.01% solution of the systemic fungicide pyrifenox. Further foli ar sprays of mono- or dipotassium phosphate, sodium bicarbonate (1%) a nd pyrifenox remarkably suppressed powdery mildew colonies on diseased foliage. Solutions of 25 mM of mono- or dipotassium phosphates and po tassium nitrate applied on a 7 or 14 day schedule were highly protecti ve against natural infection by the mildew fungus in the greenhouse. P yrifenox was not significantly more effective in controlling S. fuligi nea than either phosphate or the potassium salts. These salt solutions were not phytotoxic to plant foliage. The inhibitory effectiveness of phosphate and potassium salts makes them useful biocompatible fungici des and possibly ideal foliar fertilizers for disease control in the g reenhouse.