Determining the critical time for weed removal (CTWR) is essential for the development of an integrated weed management plan. Therefore, field experiments were conducted to evaluate the effects of two planting patterns (standard and twin-row) with and without PRE-applied herbicides on CTWR in corn. Experiments were laid out in a split-plot arrangement with two main plots: (i) standard row planting (SRP) that is 70 cm wide, and (ii) twin-row planting (TRP) with 50 cm distance between each set of double rows. Each main plot was divided into two sub-plots (with and without PRE herbicides). The sub-sub-plots consisted of seven weed removal timings for PRE herbicides, and tank mixes were utilized (S-metolachlor (1.44 kg a.i. ha⁻¹) + terbutylazine (0.75 kg a.i. ha⁻¹)). The CTWR without PRE herbicides was similar in both the SRP and TRP systems, where it was around the V1 to V2 (16 to 19 d after emergence (DAE)) growth stages. The use of PRE-applied herbicides delayed CTWR in SRP to the V4 to V10 (25 to 58 DAE) stages and up to the V11 (60 DAE) stage in TRP. These results clearly indicate that PRE herbicides are important for protecting corn yields regardless of the planting pattern. In more meteorologically favorable seasons (sufficient heat and precipitation) in both sowing systems, corn plants produce their biological maximum with the fact that over the number of plants per unit area (SRP = 80,000 plants ha⁻¹, TRP = 93,900 plants ha⁻¹) provide higher yields in variants with PRE herbicides, and thus the advantage of the TRP system can be justified.

The crop yield can be affected by many factors, including various levels of weed presence. Therefore, we conducted a study to evaluate the effect of time of weed removal in combination with planting pattern and pre-emergence-applied herbicides on maize yield and yield components in 2015, 2016 and 2017. The experiments were designed in a split–split plot arrangements with three replications, which consisted of the two main plots (standard/conventional and twin-row planting pattern), two subplots (with and without pre-emergence herbicide application) and seven sub-subplots (seven weed removal timings). In the dry season of 2015, maize yield was much lower (413–9045 kg ha⁻¹) than in the wet 2016 seasons with yields of 5759–14,067 kg ha⁻¹ across both planting patterns. Yield and yield components were inversely correlated with the time of weed removal. The application of pre-emergence herbicides delayed the critical time for weed removal (CTWR), which ranged from V4 to V10 and from V3 to V11 for standard and twin-row planting patterns, respectively. Herbicides also protected various yield components, including 1000 seeds weight and number of seeds per cob.

Wild hemp (Cannabis sativa L. ssp. sativa var. spontanea) is a special variety of industrial hemp (Cannabis sativa L. ssp. sativa), which is believed to have originated from the acclimatization of industrial hemp to the ruderal habitat conditions of Eastern Europe. In Serbia it is found along roads, on field edges, stubble fields, garbage dumps etc., but also as a weed in fields. Due to the great popularity of industrial hemp, which can be used for various purposes (as raw material in food and pharmaceutical industry, in the production of gluten-free flour, biodiesel, detergents, in folk medicine), many researchers have analyzed its seeds, including analysing their fatty acids content. However, even though this knowledge can be of chemotaxonomic, ecological, evolutionary and nutritional significance, there is no data on the presence and composition of fatty acids in wild hemp seeds For the analysis of fatty acids in wild hemp seeds, the seed material was collected from two locations. After the extraction with hexane, determination of fatty acid esters was performed by capillary gas chromatography. Chromatographic peaks in the samples were identified by comparing the retention times with the retention times of the fatty acid esters in the analytical standard of a mixture of 37 fatty acid esters. The fatty acid composition is expressed as the relative mass fraction of the total fatty acids. The analysis of fatty acids in wild hemp seeds reveales the presence of 15 different acids, with content of 17.5% (U1) and 14.7% (U2) in relation to the total seed weight. Linoleic (45.3 and 47.5%) and a-linoleic (13.6 and 15.5%) acids were the most dominant. Of the 15 detected fatty acids, only 4 are saturated, with a representation of about 12%. Unsaturated fatty acids are present in a significantly higher proportion (about 88%), which indicates the nutritional value of these seeds.