The effect of herbicide Flex, AS (active ingredient fomesafen 250 g/l) on annual weed species common in soybean crops was studied. The studies were conducted under greenhouse conditions in 2019-2021. The sensitivity of ragweed Ambrosia artemisiifolia L., Asian copper leaf Acalypha australis L., common lamb's quarters Chenopodium album L., common dayflower Commelina communis L., China jute Abutilon theophrasti Medik, trailing hollyhock Hibiscus trionum L., St.-Paul’swort Sigesbeckia pubescens Makino, green amaranth Amaranthus retroflexus L., elsholtzia Elsholtzia pseudocristata Levl. et Vaniot, and Siberian cocklebur Xanthium sibiricum Patrin ex Widd was determined. Weed treatment with Flex at rates of 0.75, 1.0, 1.25 and 1.5 l/ha was carried out three times a season at different stages of plant growth and development. The level of sensitivity of weed species to herbicide was judged by the decrease in height and weight of the aboveground organs of the experimental plants compared to the control. It was found that Flex herbicide completely destroys plants of all tested species in the early stages of growth and development (1-4 true leaves). When treating weeds that have formed 3-10 leaves, ragweed, green amaranth, Asian copper leaf, trailing hollyhock and Siberian cocklebur remain highly sensitive to the drug action (reduction of the aboveground weight up to 94-100%). Application of Flex on overgrown plants leads to a significant decrease in its activity against all studied weed species. When used in the third term, the herbicide is effective only on the green amaranth, suppressing the mass of the plants by 76-86%.

The results of the study of the weed component of soybean, early grain crops and maize agrocenoses in Primorsky Territory are presented. In total, 111 species of weeds belonging to 35 families were found during the period from 2016 to 2020. Compared with the results of crop surveys conducted in 2006-2015, the total number of species detected has increased by 23. The largest number of species belongs to the families Asteraceae (24), Poaceae (15), Polygonaceae (11), Fabaceae (9), Brassicaceae (8), Caryophyllaceae (7) and Lamiaceae (5). The remaining 26 families were represented by 1-3 species each. For the first time weeds-representatives of the families Scrophulariaceae, Violaceae, Lythraceae, Onagraceae, Asclepiadaceae and Boraginaceae have been discovered. The floristic composition of soybean agrocenoses was the highest with 108 weed species from 31 families. In cereal and maize crops, weed diversity was less significant, with 75 species in 22 families and 72 species in 25 families, respectively. Weed vegetation in all the above crops is represented by 62 species of 19 families. The main weed species that grew on 97-99% of the surveyed territory with a sufficiently high average density of standing (21-61pcs/m2) were Asian copperleaf, cockspur grass and common ragweed. Also, more than half of the surveyed crops of soybeans, cereals and corn were hairy cupgrass, perennial sow thistle, common couch-grass, common lamb’s quarters, wormwood species, field horsetail, yellow thistle, dayflower and yellow foxtail. Practical measures to protect against weeds on the Primorsky Territory should be primarily aimed at controlling these species.

The results of the study of toxicity level for the lamb's quarters (Chenopodium album L.) of well-known herbicides used in soybean crops as well as herbicides promising for soybean production in the Far East are presented. Lamb's quarters (Chenopodium album L.) is a highly noxious weed species that is widespread in the south of the region. Weediness monitoring conducted in 2006-2020 showed that this species was present in the Primorsky Territory on 63-100% of fields occupied by soybeans with an average growth density of 3-117 pcs/m2. In 2013-2020 in a series of experiments, conducted in the conditions of the vegetation house and on the experimental fields of the institute, the toxicity level for Common lamb's quarters was determined by 20 herbicides (based on 14 active substances) used in soybean crops. It was found that the control of this weed species is most effective when applying herbicides in the soil and treating plants with a height of up to 4-11 cm at the early stages of development - 1-3 pairs of leaves. Reliable suppression of lamb's quarters in experiments was provided by the soil (before sowing or before soybean seedlings) use of herbicides containing active substances metribuzin, imazetapir, trifluralin, pendimetalin and acetochlor. Among the active ingredients of the tested foliar herbicides, fomesafen, combinations of bentazone + acifluorfen and imazamox + chlorimuron-ethyl were the most toxic for lamb's quarters. It is recommended to use the following herbicidal preparations to control the spread of lamb's quarters: before sowing or sprouting of soybeans - Lazurit, Zenkor Ultra, Pivot, Proponit, Fabian; for processing vegetative plants - Flex, Galaksi Top, Concept, Classic Forte (Harmony Classic), Proponit.