Effect of selected essential oils on the efficacy of volunteer oilseed rape control and phytotoxicity in maize plants

The presence of weeds in cultivated fields can significantly reduce the yield of crops. In recent years, however, more and more attention has been paid to limiting the amount of chemical plant protection products used in agriculture. Numerous studies are carried out using substances of natural origin, like essential oils, as herbicides, fungicides and insecticides. In the conducted experiment, the use of clove (Eugenia caryophyllus (Spreng.) Bullock & S.G. Harrison) and pine (Pinus sylvestris L.) essential oils applied pre- and post-emergence as herbicides was investigated. Commercial source materials were selected. Emulsifed essential oils were applied at 5, 10, 15, and 20 L [ha.sup.-1]. The test plants were winter oilseed rape (Brassica napus L. subsp. oleifera (Delile) Sinskaya) and maize (Zea mays L.) The comparative herbicides were mesotrione and terbuthylazine (applied in doses registered in maize cultivation). Pre-emergence treatment was performed 1 d after sowing, and post-emergence essential oils and herbicide were applied when oilseed rape was in the 2-3 leaf stage and the maize was in the 3-4 leaf stage. Clove essential oil applied post-emergence contributed to the damage to both plant species (3 d after treatment: 7.5%-46.3% damage of volunteer oilseed rape; 2.5%-25.0% damage of maize, depending on dose). It also influenced the maximum photochemical efficiency of photosystem II. However, its effect was transient, unlike the synthetic herbicide. Applied pre-emergence, it did not affect the development of maize and rape (0% plant damage). Pine essential oil did not damage the test plants in soil and foliar application (0% plant damage). Key words: Brassica napus subsp. oleifera, clove, Eugenia caryophyllus, mesotrione, phytotoxicity, pine, Pinus sylvestris, terbuthylazine, weeds.