SUMMARYRumex crispus L. is an invasive species widespread in our country and in particular in the region of North Bulgaria. It is characterized by high biological and ecological plasticity. Owing to its great reproductive potential, the weed has been assigned to the list of economically most important weeds in the country.With the purpose of studying the possibility of chemical weed control in noncropped areas with heavy natural background infestation with R. crispus L. and other dicotyledonous weeds, two field trials were carried out. A ready-to-use herbicide mixture 2,4-D 140.2 g/l -1 + Triclopyr 144 g/l -1 , trade product Genoxon 3X (X0050), was tested at two doses of active ingredient, 3552 and 2842 ml/ha -1 . It was found that: (1) population density of Rumex crispus L. can be successfully reduced by treatment at the stage of early stem formation; herbicide efficacy with 3552 and 2882 ml/ha -1 doses on the 21 st day after treatment was 100% and 90.5%, respectively, at the end of vegetation 94.4 and 85.7%, respectively; (2) herbicidal efficacy was lower when R. crispus L. was treated at the 5 -6 leaf stage, being 100 -94.1% and 80 -76.5% respectively for the indicated doses and time of recording; (3) at the studied doses the herbicide controlled both annual dicotyledonous weeds (Amaranthus spp., Chenopodium album L., Portulaca oleracea L.) and perennial dicotyledonous ones (Cirsium arvense L., Sonchus arvensis L., Convolvulus arvensis L., Carduus acanthoides L.), but it was not toxic to monocotyledonous weeds.

SUMMARYDuring the period 2008-2010, on the experimental field of the Institute of Forage Crops -Pleven, on slightly leached chernozem a study was conducted with the purpose to determine the selectivity of some herbicides to perennial ryegrass (Lolium perenne L.), and their influence on the seed productivity. As a result of the study the following was found: herbicides for broadleaf weeds control -Arat (500 g/l dicamba + 250 g/l tritosulfuron) at rate of 100 ml/ha, Korida 75 VDG (750 g/kg tribenuron-methyl) -15 g/ha and Cambio SL (320 g/l bentazone + 90 g/l dicamba) -1250 ml/ha had high selectivity to perennial ryegrass, applied at 2-4 leaf stage during establishing year of the stand and until the stage of the beginning of shooting up in seed production year. Herbicide for grass weeds control: Topik 080EK (80 g/l clodinafop-prop-argyl + antidote) at rate of 300 ml/ha, applied at the same stage can be applied in seed production stands of perennial ryegrass. Herbicide for grass weeds control -Grasp 25SK (250 g/l tralkoxydim) + Atplus 463 at rate of 1000 + 1000 ml/ ha showed phytotoxic effect on L. perenne and caused the reduction of seed and dry biomass productivity. Realization of the biological potential concerning seed and dry mass yield of perennial ryegrass demands application of selective herbicides Arat, Korida 75 VDG and Cambio SL in control of broadleaf weeds and Topik 080EK in control of grass weeds.

SUMMARYDuring the 2007-2009 period in the experimental field of the Institute of Forage Crops a study was conducted with the purpose of investigating the effect of weeds and some methods for their control in seed production stands of sainfoin (Onobrychis viciifolia Scop.). The trial was carried out on a slightly leached chernozem on an area with a natural background of weed infestation. As a result of the study it was found:Establishment of very uniform and productive seed production stands of sainfoin required effective weed control concentrated mainly in the first year when the degree of weed infestation was the highest and reached to a number of 245 plants/m 2 and the fresh weed biomass to 1311 g/m 2 .The chemical control method showed the highest efficacy had the highest efficiency when, in the year of stand establishment at the stage of second-fourth true leaf of sainfoin, the treatment was conducted with imazamox 40g/l (Pulsar 40) at the dose of 48 g a.i./ha or with the system of Bentazon 600 g/l (Basagran 600 SL) -900 g a.i./ha -fluazifop-P-butyl g/l (Fusilad Forte) -120 g a.i./ha. In the years of seed production in spring at the beginning of vegetation, the treatment was conducted with imazamox 40 g/l (Pulsar 40) at the dose of 20 g a.i./ha + adjuvant DESH at the dose of 1000 ml/ha.An alternative to the chemical method is to sow sainfoin under cover of spring barley achieving more complete use of the area in the first year, a weed suppressive and ecological effect, but some negative residual effect on the crop was also observed;The pure stands of sainfoin with chemical control of weeds had the highest seed productivity, exceeding the zero check by 24 to 28%, followed by the stands with spring barley as a cover crop with an increase of 12% and the mixed stands of sainfoin with crested wheatgrass had the lowest productivity.

SUMMARYA study was conducted in a pure stand of lucerne (variety Viktoria) Statistically significant (P<0.05) functional relations were found between the chemical characteristics and percentage of Capsella bursa pastoris (L.) Medic. participation in the lucerne sward, and forage quality. These relations indicated a multiple practical relevance and a necessity to control Capsella bursa pastoris (L.) Medic. in lucerne stands in order to decrease weed density and improve forage quality.

SUMMARyThe study was conducted to determine selectivity of some herbicides to cocksfoot (Dactylis glomerata L.), and their influence on the seed production, during the years 2008-2010. The trial was set on the experimental field of the Institute of Forage Crops -Pleven, on slightly leached chernozem. As a result of the research the following was found: herbicides Arat (500 g/l dicamba + 250 g/l tritosulfuron) at the dose of 100 ml/ha, Korida 75 VDG (750 g/kg tribenuron-methyl) -15 g/ha and Cambio SL (320 g/l bentazon + 90 g/l dicamba) -1250 ml/ha and Grasp 25SK (250 g/l tralkoxyidim) + Atplus at rate of 1000 + 1000 ml/ha had high selectivity to cocksfoot, applied at 2-4 leaf stage during establishing year of the stand, and until the stage of the beginning of shooting up in seed production year.Herbicide Topik 080EK (80 g/l clodinofop -propargyl + antidote) at rate of 300 ml/ha, showed phytotoxic effect to D. glomerata and caused the reduction of seed and dry biomass productivity.