In the years 2000-2002 the evaluation of herbicides' efficacy used in lowered doses was conducted. Six herbicides recommended for weed control in spring cereals were used for investigation. The majority of species of weeds occurring in spring wheat and spring barely reacted with a strong (above 90%) decrease of the fresh weight to the treatment with the herbicides applied in the doses reduced by 25%-50% in relation to the recommended ones. Polygonum convolvulus L., Polygonum persicaria L. and Thlaspi arvense L. were very sensitive species as they were very good controlled by tested herbicides in the doses decreased by 50%-75%. Veronica hederifolia L. and Viola arvensis Murr. were characterised by a low level of sensitivity and were controlled only by full recommended doses of tested herbicides. The significant statistical decrease on yield of spring wheat on the objects treated with the herbicides Aurora Super 61,5 SG (mecoprop-P+carfentrazone-ethyl), Granstar 75 DF (tribenuron-methyl) and Grody! 75 WG (amidosulfuron) in the doses lowered by 50% in relation to the recommended ones and Starane 250 EC (fluroxypyr) and Chwastox Trio 540 SL (mecoprop+MCPA+dicamba) in the dose lowered by 50%-7 5% was not observed. In the case of the herbicide Aminopielik D 450 SL (2,4-D+dicamba) the reduction of the dose by 25%-50% also did not cause decrease on yield of spring wheat. In the spring barley, the significant statistical decrease of yielding was not observed on all treatments with tested herbicides applied in the doses reduced by 50%-75%.

In the years 1996-2002 evaluation of herbicides' efficacy used in low doses was tested. For investigations several herbicides recommended for weed control in cereals were selected. The results of experiments indicate on possibility of reducing of herbicides' doses by about 25 to 3 7.5%, and still obtaining good effects ofweed control without significant decrease of yielding of cultivation plants. The dose is depended upon sensitivity of weed species, growth stage of weeds and their infestation, density of crop and the weather conditions. Low doses of herbicide can be applied where weeds are in early growth stage, where there is low infestation ofweeds, and weeds show susceptibility to used herbicides, moreover under correct crop density and good weather conditions.

The outdoor pot experiments on the influence of weeds' growth stage and climate conditions on herbicides' effect were carried out in the Danish Institute of Agriculture Science in 2000-2001. The experiment concerning growth stage took into consideration three phases of Galium aparine: l, 2 and 3 whorls. The influence of temperature was performed using climate simulator running at three temperatures: 8/2°C, l 6.5/8°C, 24/16°C. The rain was applied using rain simulator 1, 3 and 6 hours after herbicides' treatment. Herbicides: Grody! 75 WG (amidosulfuron 750 g*kg-1), Aurora Super 61,5 WG (mecoprop 600 g=kg' + carfentrazone-ethyl 15 g*kt1), Lintur 70 WG (dicamba 65.9 g=kg', triasulfuron 4.1 g=kg') and Chwastox Trio 540 SL (dicamba 40 g*r1, MCPA 200 g"l', mecoprop 300 g*r') were applied in four doses: full recommended, 1/2, 1/4 and 1/8 of full dose on G. aparine. Grody! 75 WG and Aurora Super 61,5 WG were the most efficient to the youngest plants of G. aparine. Differences in susceptibility among three growth stages (1, 2, 3 whorls) to Grody! 75 WG were higher than to Aurora Super 61,5 WG. Effectiveness of tested herbicides tended to increase as temperature rose. The addition of adjuvant improved activity of herbicide Lintur 70 WG that showed satisfactory weed control even at four time reduced dose independently from temperature. The rain treatment 1, 3 and 6 hours after spraying caused reduction of Aurora Super 61,5 WG activity at 1/4 and 1/8 doses. The half dose gave a good result only when rain was applied 6 hours after treatment. Herbicide Grody! 75 WG was efficient after rain application (1, 3, 6 HAT) only at full dose.