<p class="R-AbstractKeywords"><span lang="EN-GB">Integrated weed management (IWM) is a complex approach to weed control that is based on use of several different methods complementing each other, instead of relying on one single method, like chemical weed control. Weed control methods that can be used as parts of IWM strategy include mechanical weed control, application of herbicides, low tillage, changes in the rate and application time of fertilizers, use of undersown crops and crop rotation. Weed surveys were carried out in 2013 and 2014 in the southeastern part of Latvia. The aim of this study was to assess the effect of crop rotation and other field management practices on weed density and weed species composition using the data collected in the surveys. Survey was carried out in the arable fields of conventional farms within four different size categories. One of the significant factors that explained the variation of weed composition within a field was a proportion of cereals in crop rotation within a four year period. Further surveys are required to estimate the effects of climatic variables. Density-dependence can also be important for practical management decisions for particular weed species and should be investigated.</span></p>

Wild oat (Avena fatua L.) is the most serious weed infesting cereal fields in Latvia. To predict possible yield loss at different wild oat densities field trials were established in four consecutive years, each year in a different spring wheat field in the southern part of Latvia. Growth dynamics and biomass of both crop and wild oat and grain yield were measured. Yield loss model developed by Cousens (1985) and exponential decay model were fitted to the data from each year. Grain yield and biomass of both spring wheat and wild oat significantly differed between the years. The average grain yield of spring wheat in all treatments was 4443.38-7127.02 kg ha -1 . The targeted wild oat density was 0, 1, 2, 4, 8, 16, 32, 100, 200 and 500 plants m -2 . The achieved density in the field trial reached from 0 to 332-466 plants m -2 . The emergence of wild oat seedlings lasted for 35 to 56 days after sowing, depending on the year. The initial hypothesis that low wild oat plant density may cause grain yield loss of spring wheat was supported by the results of the field trials. There was substantial variation in model parameters among the years of the trials, 5% yield loss was estimated to result from wild oat density ranging from 3 to 54 plants m -2 in different years. The variation of spring wheat yield loss and wild oat competitiveness might be explained by different meteorological conditions in the years 2013-2016 and different nutrient supply in the trial fields. Further research is necessary to find the most influential factors that determine yield loss caused by wild oat. The results are important to raise awareness of the harm caused by wild oat in cereals in the Baltic region.