Small plot trials were carried out in years [2001][2002][2003] with sugar beet. In the treatment without weed control, dry weight of sugar beet top and LAI of sugar beet were very low (approx. 50 g/m 2 and 0.5 m 2 /m 2 , respectively). Yield loss of sugar beet was 80-93%. Dominant weeds were Chenopodium album, Fumaria officinalis and Galium aparine. In the treatments where weeds were removed (by hand) until 4 leaf stage of sugar beet, dry weight of sugar beet top and LAI of sugar beet at first increased normally, but were markedly decreased from the half of the vegetation period. Yield loss of sugar beet was 54-28%. Dominant weed in this treatment was Amaranthus retroflexus. The development of sugar beet top dry weight and LAI of sugar beet was practically identical in the treatments where weeds were removed until 8-10 leaf stage of the crop and in those where weeds were removed during the whole vegetation period (500-900 g/m 2 , or 4-7 m 2 /m 2 , respectively). No yield loss of sugar beet was recorded. Dry weight of weeds did not exceed 30 g/m 2 and LAI 0.1 m 2 /m 2 . A. retroflexus and Mercurialis annua were the most frequent weeds in this treatment.

Laboratory experiments were carried out with seeds of Galinsoga ciliata and Chenopodium album in 1998, 2000 and 2001. The study involved germination of non-dormant seeds in the light and the dark at 5-30°C, the germination energy at 15, 24, and 33°C, and the primary dormancy of seeds matured during the period from July to October. Both weeds germinated better in the light compared to the dark. Seeds of G. ciliata germinated at 10-33°C. Germination exceeding 85% was recorded at 12-28°C. Ch. album germinated in a wider temperature interval (5-33°C). Maximum germination (75%) was obtained at 18°C. A very high germination energy of G. ciliata seeds was found at 24°C. At this temperature, 89% of seeds germinated during the second and third day of the germination test. Seeds of Ch. album had a low germination energy at 15 and 24°C. The germination energy was high only at 33°C, however, the total germination reached at this temperature was only 26.5%. Both G. ciliata and Ch. album formed primary dormant seeds during all three testing years. The length of primary dormancy varied from 10 to 100 days depending on the date of ripening and on the year. The longest primary dormancy was found with early ripened seeds (July and August).

Competitive ability of six summer catch crops (Brassica napus, Lolium multiflorum, Lolium perenne, Phacelia tanacetifolia, Sinapis alba and Trifolium incarnatum) in volunteer winter wheat based on field trials was experimentally tested during the years 2004-2007 in central Bohemia (Czech Republic). The production of aboveground biomass and plant cover of sown catch crops, volunteers and weeds was assessed on experimental plots. General linear models revealed significant influence of catch crops, year and their interaction on dry-mass of the volunteers. The lowest average values of volunteer biomass at the end of growing season (average from [2004][2005][2006][2007] were recorded on plots sown with S. alba (124.7 kg/ha) and P. tanacetifolia (186.3 kg/ha). The average biomass of volunteer plants in stands of S. alba was significantly lower than the biomass of volunteers in stands of L. perenne, L. multiflorum and T. incarnatum. The lowest average biomass of weeds was recorded also in S. alba stands. In the context of our study, catch crop is a crop sown between seasons of regular plantings to make use of temporary idleness of the soil.

The aim was to compare the efficacy, selectivity to sunflower and dissipation of three chloracetamide herbicides (acetochlor, metolachlor and pethoxamid) in dependence on precipitation after application. A small plot field trial was carried out with sunflower in Central Bohemia in 2010 and 2011. The remaining concentration of active ingredient in the soil of all studied herbicides was lower in the year with a higher temperature and a low level of total natural precipitation at the beginning of the growing season. Higher leaching of metolachlor and pethoxamid was recorded in irrigated plots. No leaching was found in the case of acetochlor. The highest leaching was found for metolachlor (9.2-25.5% in soil layer 5-10 cm). The highest phytotoxicity was found for acetochlor (9.8%) > pethoxamid (4.6%) > metolachlor (1.8%). The mean phytotoxicity in the irrigated plots was 6.9%, compared with 3.9% in the non-irrigated plots. The efficacy of the tested herbicide was affected by wet conditions. The highest efficacy on Chenopodium album, Amaranthus retroflexus, Echinochloa crus-galli and Solanum physalifolium was recorded after application of acetochlor and irrigation.

Whole-plant glasshouse bioassays, enzyme assays and field experiments were conducted to examine the sulfonylurea herbicide resistance pattern in Apera spica-venti populations from the Czech Republic. Varying, but very high levels of resistance to chlorsulfuron, sulfosulfuron and iodosulfuron were found, and cross-resistance to all three herbicides was confirmed. In dose-response glasshouse studies, resistance factors (GR 50 ratios relative to a susceptible standard) were above 230 for chlorsulfuron, 115-270 for sulfosulfuron and 27-148 for iodosulfuron. A biotype originating from Lomnice that was cross resistant to the three herbicides was also highly resistant to sulfometuron-methyl. Concentrations of herbicides required to inhibit acetolactate synthase (ALS) enzyme activity by 50% were substantially higher (up to 4000 times) for all three resistant populations, compared with the reference susceptible population, indicating that the A. spica-venti populations have ALS enzymes that are highly insensitive to the tested sulfonylureas. The differences in the spectra of resistance suggest that the sulfonylurea resistance mechanisms may differ among biotypes. The field experiment was designed to compare the control effect of selected sulfonylureas (chlorsulfuron and iodosulfuron), isoproturon and fenoxaprop-P-ethyl on ALS-resistant populations. Sulfonylurea herbicides failed to control resistant populations, but these were well controlled with alternative mode of action herbicides, thus demonstrating practical options for weed management.