Biology and control of sugar beet significant weeds:: Perennial sow-thistle (Field sow-thistle) Sonchus arvensis L.

Possible acting of Sonchus arvensis as a weed in crop stand is limited by crop competition ability (usually rapidity of LAI increase), density of the crop canopy, and by the term of sowing. In dense canopies of early sowed spring cereals the infestation of this weed is mostly prevented. Compared to Cirsium arvense, this species has weaker and less dense root system with minimum rhizome dormancy so its management is easier. In sugar beet stands, sufficient chemical control can be achieved only by herbicides with active ingredience clopyralid. in spite of the fact that there can occur crop phytotoxicity effects after herbicide application and that S. arvensis emerges irregullary during long period, herbicide control with this active ingredience is recommended to be realized in split application (during second and third term of herbicide application in sugar beet stands). Not only herbicides but also Cultural practices can provide effective management of this weed species. Among them, deep and high quality tillage has got a high influence. Vulnerable rhizomes are easily broken into small segments which emerge consequently and can be controlled by efficient herbicides.