Sorghum halepense (L.) Pers. belongs to highly invasive weed species. In mid-1900s, the cultivation of this species as a forage crop led to its invasiveness (Peerzada et al., 2017). Yield losses it causes are up to 57-88% on very important agricultural and horticultural crops (Peerzada et al., 2017). It is highly tolerant to herbicides and rapid vegetative growth makes it difficult to control. Finding new methods that will help combat invasive species with less environmental impact is gaining importance. Allelopathy is very important for finding new compounds that can be used to combat invasive weeds (Arora et al., 2015). Allelochemicals are very important in relationship between plants and their environment (Cespedes et al., 2014). McPartland (1997) points to repellent and pesticidal properties of Cannabis sativa L.The aim of this study is to investigate allelopathic effect of C. sativa L. extract on lipid peroxidation activity in leaves of treated plants of S. halepense (L.) Pers.Extract obtained by the classical extraction process was applied at concentrations of 100%, 50%, 25% and 10%, while the control variant was not treated. Plants of S. halepense L. (Pers.) were in the initial stages of growth when extract was applied. Experiment was performed under field conditions. Plants respond to adverse environmental effects by changes in biochemical processes (Sunmonu & Van Staden, 2014). Sampling of treated plants was performed after 6h and 24h. Biochemical analyzes of fresh leaves of S. halepense (L.) Pers. lipid peroxidation activity was determined.C. sativa L. extract caused changes in the lipid peroxidation activity of S. halepense (L.) Pers. Increased activity was only in variant of application of the highest concentration of extract with a statistically significant difference in both sampling moments. Value of monitored activity in control variant was 73.18 nmol MDA / g SBM while in variant with 100% application of the extract it was 99.36 nmol MDA / g SBM after 6h. After 24 h, a value of 100% extract of 80.02 nmol MDA / g SBM was obtained, as opposed to control with a lipid peroxidation value of 68.27 nmol MDA / g SBM. Other variants of application did not show statistically significant differences with respect to control after 6 h from moment of treatment. Less pronounced differences in obtained values were observed in variants with 50%, 25% and 10% compared to control after 24 h.An increase in lipid peroxidation activity in variants using 100% C. sativa L. extract is a response to plant exposure to stress, thus proving an allelopathic effect on treated plants.

Summary Allelopathic effects of different plant allelochemicals have become the focus of studies that aim to determine new pesticidal compounds. Plant extracts with different chemical compositions can be obtained using different methods of extraction, whereas studies dealing with allelopathic properties use biotests to obtain fast and precise results. Such studies were undertaken after noticing the allelopathic effects of industrial hemp (Cannabis sativa L.) on the surrounding crops. Trials that involve the application of hemp extracts obtained by different methods resulted in determining the hemp allelopathic effects on Stellaria media (L.)Scop., Beta vulgaris ssp. vulgaris var. vulgaris, Lupinus albus L., corn (Zea mays L.), Cyperus rotundus L., Matricaria recutita L., Lepidium sativum L., lettuce (Lactuca sativa L.), rapeseed (Brassica napus L.), wheat (Triticum aestivum L.), rye (Secale cereal M. Bieb.), Ambrosia artemisiifolia L., Chenopodium album L., and Sorghum halepense L..