THE EFFECTS OF PLANT-EXTRACTS OF REYNOUTRIA-SACHALINENSIS ON POWDERY MILDEW DEVELOPMENT AND LEAF PHYSIOLOGY OF LONG ENGLISH CUCUMBER

An aqueous formulation of concentrated extracts (Milsana flussig) from leaves of the giant knotweed, Reynoutria sachalinensis, applied weekl y at a concentration of 2%, provided control of powdery mildew (Sphaer orheca fuliginea) on long English cucumber that was as effective as be nomyl. In two separate experiments, this treatment significantly reduc ed the severity of powdery mildew compared to control plants. Fruit yi eld was not affected by the treatment, even though repeated applicatio ns of Milsana induced a greener and glossier coloration of the leaves, which became brittle to the touch. A rapid and distinct accumulation of fungitoxic phenolic compounds occurred in leaves treated with Milsa na, especially in infected leaves. A slight inhibition of conidial ger mination was the only direct effect of Milsana on S. fuliginea. These results support the hypothesis that Milsana may act indirectly by indu cing plant defense reactions and that it may be useful in the integrat ed management of cucumber powdery mildew.