Milk thistle – Silybum marianum (L.) Gaertn. can be a winter annual or a biennial medicinal plant. The assessment of the occurrence of milk thistle in sustainable crop rotation was conducted at the Experimental Base of Faculty of Agrobiology and Food Resources, SUA in Nitra in the years 2008- 2011. This study was focused on milk thistle as a weed in the sustainable farming system with the crop rotation of maize for grain, pea for grain, durum wheat and milk thistle. An actual weed infestation of maize, pea and durum wheat stands with milk thistle was evaluated before preemergence application of herbicides, in the spring time. Second screening of actual weed infestation of all stands in sustainable crop rotation with milk thistle was done before crops harvest. Screening of each field was made on 1 m 2 area with three replications. The three randomly established sample quadrants were situated minimally 10 m from field margin and apart from each other, respectively. The level of infestation was evaluated according to average density of weeds per square meter. Obtained data was statistically analyzed by Statistica 7.0, ANOVA, LSD test (p=0.05). As a plant from the family Asteraceae has a great anticipation to have vital seeds in soil profile for long time as well as Helianthus annus. On the base of our 4 vegetation periods research, we can conclude that the S. marianum seeds are vital in soil profile for three and more years. We can also conclude that in third year after milk thistle cropping was no infestation of durum wheat, but S. marianum germinate after the harvest of durum wheat at the stubbles in August or September. According to statistical analyses in the year 2010 was the maize stands infested with the highest, statistically very significant amount of Silybum marianum (7 plants per m 2 ). Stands of pea for grain in the second year after milk thistle cropping were infested in the years 2008-2010 only with 0.33 plants per m 2 . Durum wheat stands were not infested with milk thistle. In the spring time the infestation of maize for grain, pea for grain and durum wheat stands with milk thistle falled very significantly down from 17.78 plant pre m 2 in maize stand to 2.56 plant pre m 2 in durum wheat stand. The originality of this paper is in the examination of new perspective crop in sustainable farming systems and in evaluating of its weed potential.

weed infestation, Sylibum marianum L. Geartn., sustainable crop rotation

Presentation: oral