The powdery mildew is one of the dangerous diseases of wheat, which can cause decrease of grain yield and quality. The mildew damaged the winter wheat in the vegetation period on the experimental fields of the Bila Tserkva national agrarian university during 2010-2012.

The causative agent of the disease is the fungus Erysiphe graminis DC. F. tritici March. It strikes the unstable varieties and the sporulation on these varieties is going faster. The plants resistance to the fungus depends on their age. The older winter wheat is getting less resistant to the fungus. The contamination of the plants depends on the weather condition, which affects the fungus development cycle. The development cycle of the Erysiphe graminis DC. F. Tritici begins with powder like white incrustation on the leaves and sprouts. It is created by the superficial mycelium, sticking to the surface of the damaged plants by means of appressorium, and by short unbranched conidium carriers with unicellular oval conidia, located on their top like a chain. The conidia cause the contamination of the plants by erysiphosis during their vegetation. If weather conditions favorable, the contamination can occur several times per vegetation.

At the end of the vegetation, some visible small black drops emerge on the mycelium. These are the mycothalli – cleistothecia, the wintering sexual stage of these fungus. In spring or beginning of summer, the mature cleistothecia burst and the liberated ascospores contaminate the plants for the first time by the powdery mildew.

The mycothalli of erysiphic fungus are a transition form from cleistothecium to perithecium. They are spherical, closed, however their asci are located not irregularly but in a bunch or solid sphere. If the asci capsules burst, the ascospores get out actively. The damage records of the winter wheat by the powdery mildew were carried out by means of the five-mark grading scale of Y.Y. Heshele.

During the trial period, the winter wheat has been damaged by the powdery mildew throughout vegetation period. The varieties Ermak and Poliska 90 were affected most of all at the beginning of booting ranging between 64,4-73,2%, with disease development degree 2,03-2,23% and after earing 95,3-97,2 and 2,13-2,34%. More immunity to the powdery mildew was shown by the varieties Podolyanka (St) and Elegia at the beginning of booting. Their yield was 34,9-44,2% and the disease development degree 1,08-1,85%, and one week after earing 55,7-68,1 and 1,71-1,99%.

The damage of the winter wheat varieties by the powdery mildew fungus was influenced by the weather conditions during trial period. In 2010, some slight increase of average daily temperature by +3,3^oC was noticed compared to average of several years. Also the precipitation index decreased by 54,8%. The winter wheat was insignificantly damaged by the powdery mildew during vegetation period.

The spring 2011 was early and favorable. During spring months, the weather was warm with insignificant deviation from the many years’ indexes. This fostered the fast development of pathogen on the grain crops and the increased precipitation in May-June caused the epiphytotic development of powdery mildew fungus.

As to the vegetation 2012, some insignificant trend for increase of the average daily temperature by +2,6^oC compared to the average of many years was noticed as well as not even distribution of precipitation during vegetation period by 10,5%. The disease development was on average level compared to the trial years.

Thus the main damage from powdery mildew was observed in 2011 whereas in 2010 and 2012 the damage was moderate.

The most yield increase was shown by the winter wheat (43,8 centner/ha) standard variety Podolyanka (St). Good yield (41,4-41,6 centner/ha) was shown by the varieties Poliska 90 and Ermak. The least yield was shown by the variety Elegia (40,4 centner/ha).

Key words: winter wheat, powdery mildew, productivity.