The article presents the results of a series of field trials conducted between 2016 and 2020 in various regions of Ukraine. The aim of these trials was to determine crop selectivity and weed control efficacy during autumn application in winter oilseed rape (Brassica napus L.) crops using a new complex herbicide, Belkar EC. The active substances of this herbicide are synthetic auxins: halauxifen-methyl (9.6 g/L) and picloram (48 g/L). It is well known that winter oilseed rape is sensitive to halauxifen-methyl. Due to this, halauxifen-methyl can only be used in winter oilseed rape crops in combination with other synthetic auxins — specifically clopyralid, whose safening effect ensures the mixture’s selectivity toward the crop. For autumn application, picloram is more suitable than clopyralid for a number of reasons. Therefore, during the development of Belkar EC, clopyralid was replaced by picloram. Because autumn application during the early growth stages of winter oilseed rape requires higher herbicide selectivity compared to spring application, the question of Belkar EC selectivity is particularly relevant. Due to the mixed nature of weed infestation in crops, it may become necessary to combine Belkar EC with other herbicides that are effective against weed species resistant to Belkar EC. Therefore, for the effective use of Belkar EC, it is necessary to verify its selectivity toward winter oilseed rape and its weed control efficacy both when used alone and in mixtures with other herbicides. In the field experiments, spraying of winter oilseed rape crops was carried out during the 2—4 true leaves stage of the crop (BBCH 12—14). The efficacy of dicotyledonous weed control by Belkar EC was compared with the performance of Galera Super SL. It was established that during autumn treatment at the recommended rate of 0.25 L/ha and at a double rate of 0.5 L/ha, the phytotoxic effect of Belkar EC on winter oilseed rape did not exceed that of Galera Super SL. At an application rate of 0.25 L/ha, Belkar EC effectively controlled a wide spectrum of dicotyledonous weed species. The application of Belkar EC in a tank mix with Butisan 400 SC did not affect crop selectivity and allowed for the inclusion of the annual grass weed loose silkey-bent (Apera spica-venti (L.) Pal. Beauv.) into the control spectrum, while also significantly increasing the control efficacy of the annual dicotyledonous weed scentless chamomile (Matricaria inodora L.). The use of Belkar EC in a tank mix with Salsa WG significantly increased the control efficacy of weeds from the Brassicaceae family, particularly flixweed (Descurainia sophia (L.) Webb.). Application in mixtures with graminicides such as Fusilade Forte EC, Agil EC, Miura EC, and Centurion EC did not affect the selectivity of Belkar EC toward winter oilseed rape or its efficacy in controlling dicotyledonous weed species. Furthermore, the efficacy of grass weed control when applied in a mixture with Belkar EC did not differ from the effect of the graminicides applied alone. The combination of the obtained results indicates that the autumn application of herbicide Belkar EC alone and in mixtures with other herbicides in winter oilseed rape crops is safe for the crop and provides effective protection against weeds during the autumn vegetation period.
Keywords: herbicides, herbicide mixtures, selectivity, weed control, halauxifen-methyl, picloram
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