Activity of antagonists and natural compounds against powdery mildew of cucurbits: laboratory and field trials

The effectiveness of antagonists and natural compounds against Powdery mildew of cucurbits (Sphaerotheca fusca) was tested both under controlled conditions and in the field, in the years 2000, 2001 and 2002. Weekly treatments were applied on leaves; the fungicide Topas®, at intervals of 14 days, and the biofungicide AQ10®, also applied weekly, were included as controls. Among the antagonists, the yeasts Rhodotorula glutinis (Rg), Cryptococcus laurentii (Cl) and Aureobasidium pullulans (Ap), applied alone or combined with additives (mineral oil or gum xanthan) significantly reduced the disease severity on melon leaves. Their activity generally resulted comparable to that of Topas® and was similar or higher than that expressed by AQ10. All the antagonists survived on the leaves in the field at high levels of population even if the climate was hot and dry. Among the natural compounds, tested on melon leaves grown in plastic pots or on cucumber grown in the field in an organic farm, mineral oil (1%), potassium bicarbonate (0.5%), sodium bicarbonate (0.5%), calcium chloride (1%) and, particularly, powder of milk (10%) significantly reduced the severity of S. fusca on leaves as much as the wettable sulphur (control). This study pointed out that antagonists and natural substances are very promising for use in organic and integrated agriculture in alternative to synthetic fungicides.