Long-term trends in amounts of weeds in sugar beet

Authors evaluated the changes and differences in amounts of weeds on site Buxany (intermediary area between maize and sugar beet production area, south-western part of the Slovak Republic), between years 1973-1974 and 1997-1998, it means in time span 25 years. Results were obtained from long-term observations of SELEKT - Research and Breeding Institute in Bucany. The influence of agrotechnics on weediness can be practically excluded, because there was always used monogerm variety and large-scale technology of sugar beet growing. Chemically untreated control plots were evaluated every time. It means that the weather conditions (temperature and rainfalls) had the influence on weediness and kind-spectrum of weeds. Average year air temperature on trial site is 9.4degree C and in the warmest months July-August it is 19.1degree C. Rainfalls are intermediary between maritime and continental climate-long-term year average of rainfalls is 568 mm, the majority of rainfalls falls in months May-July, in average 135 mm. Sum of rainfalls for vegetation period is 340 mm. Trials were established on chernozem, which had been created on loess. Content of humus varies between 1.8 - 2.3 %, in trial soil. The depth of humus horizon is 0.3 - 0.7 m and depth of arable soil is 0. - 0.4 m. There were observed the numbers of mono- and dicotyledon weeds. The second group of weeds was divided according the main vegetation season on early spring, late spring, winter and perennial weeds. Weediness varied between 15.1 - 96.5 pieces per square meter. There was observed by analysis of variance highly significant difference between the numbers of mono- and all dicotyledon weeds in favour of dicotyledon weeds. There are similar significant differences, respective highly significant differences between monogerm early weeds and individual groups of dicotyledon weeds (early spring, late spring weeds, winter weeds and perennial weeds). Highly significant differences in weediness were also between observed years, with the exception of insignificant difference between years 1997 and 1998. The incidence of Chenopodium album continually decreased by the years and on the contrary the incidence of Amaranthus retroflexus mildly had increased. On the necessity of weed control there refers the reality, that the weediness of sugar beet significantly decreases the yield of roots