Monoculture of modern cereal crops are popular due to the technical and organizationa lreasons. They are easier in crop husbandry, qua lity and product use. However, in monoculture chemical protection of crops is a norm, due to the fact that they are more susceptible to diseases, pests and sometimes weed infestation. In order to keep high and stable grain yields and quality in monoculture one has to use high inputs. Experimentally and practically it has been proved that cultivar and species mixtures can constitute an alternative to cultivar growing in pure stands. It has been found that in mixtures opperate different epidemiological and ecological factors, which lead to considerable disease reduction, pest and weed control, which finally result in higher and more stable grain yields than in barley varietes grown in pure stands. The results of two years field experiment designed to evaluate epidemiological and economical effects of winter barley cultivar mixtures are presented. The studies were carried out in two sites – experimental lStation for Variety Testing Słupia Wielka (in Wielkopolska region) and Plant Breeding Station Bąków (Opole District). This two sites were 300 km away from each other, and had different soi land meteorological conditions. In the experiment impact of different barley cultivars and their different two- and three-component mixtures were tested with reduced dosages of fungicidies on grain yield in the mixtures compared with pure stands were evaluated.

In the four-year experiment the impact of four different barley varieties and selected two-and three-component mixtures were tested. The studies were carried out at two sites: Experimental Station for Variety Testing Słupia Wlk. (Wielkopolska region) and Plant Breeding Station Bąków (Opole District) during four growing seasons (2001/2002–2004/2005). The aim of the studies was to evaluate the yield through growing barley variety mixtures in combination with reduced use of fungicide and application dose rates. Positive effects (1–15% yield increase in mixtures compared to pure stands) were observed. On the base of obtained results it can be stated that winter barley variety mixtures can constitute an alternative way of growing winter barley, especially at low-input and ecological agriculture.

In the four-year experiment the impact of four different winter barley varieties and selected two- and three-component mixtures were tested. Reduced dosages of fungicides on disease reduction in the mixtures compared with pure stands were evaluated. The studies were carried out at two sites: Experimental Station for Variety Testing Słupia Wlk. (Wielkopolska region) and Plant Breeding Station Bąków (Opole District). Observations on powdery mildew occurrence during the vegetation season were done every 7–10 days. In order to compare the disease occurrence levels on different cultivars in pure stands and on their mixtures combined with different fungicide treatments the Area Under Disease Progress Curve (AUDPC) was evaluated. On the base of the AUDPC values the reduction of powdery mildew occurring in the mixtures due to epidemiological and ecological factors functioning in mixed stands were also evaluated. On the base of obtained results it can be stated that winter barley variety mixtures combined with different fungicide treatments do reduce the powdery mildew incidence comparing to pure stands and winter barley variety mixtures can constitute an alternative way of growing winter barley, especially at low-input and ecological agriculture.