As it is reported in this Tomato Genetics Cooperative report a new powdery mildew occurred in many European countries including Bulgaria, its agent being a fungus from Erysiphaceae family. At the end of the season in 1989 with sporulation abundantly on the upper side of the leaves turned brownish and afterwards the color darkened gradually.
Our investigations point to the presence of a hyperparsite belonging to Cicinnobolus genus (perhaps C. cesati D.B.). Its ability to parasitize is rather high. It increases with the increase in relative humidity and the decrease in temperature. In the middle of October on aged tomato leaves we could detect the picnidial for of the fungus. The above mentioned hyperparasite is cultivable in nutrient medium and we consider it suitable for biological control of the new powdery mildew.
Our activities on this problem are still going on.