Giant sumpweed (Cyclachaena xanthiifolia (Nutt.) Fresen.): seed stocks, seedling dynamics, methods control

Goal. To assess the degree of danger of contamination of the sowing layer and an increase in stocks of Giant sumpweed seeds in the soil, the timing and dynamics of seedlings emergence, to develop a control pathway aimed at their reduction. Methods. The studies were carried out by route-expeditionary surveys and field experiments. The potential soil contamination was determined washing weed seeds from soil samples. Weeds were counted in 4—6-single repetitions. Results. In ruderal biotopes, the infestation of 0—20 cm of the soil layer by weed seeds has not changed since 2009 and amounted to 244.6—384.1 thousand pcs./m2. At the same time, the infestation of soils with Giant sumpweed seeds increased 2.0—2.7 times. In crops of cultivated plants, the total weediness of the soil increased by 1.8—3.5 times, and Giant sumpweed — by 4.7—12.1 times and reached 25.0—85.0 and 14.5—15.5 thousand pcs./m2, respectively. Seed germination of Giant sumpweed was observed only in the spring and early summer periods. In the Dry and Southern Steppe, Giant sumpweed emerged in the middle-end of March, in the Northern Steppe — during April, Forest-Steppe — from early May to early June. In crops of cultivated plants the density of young crops of Giant sumpweed did not exceeded 23—62 pcs./ m2, and on uncultivated lands — from 636 to 862 pcs./m2. On uncultivated lands the effective control in crops of Giant sumpweed was carried out by mowing weeds, in crops of cereals — by herbicides of leaf action in the tillering stage, late arable crops by pre- and after emergence harrowing combined with inter-row cultivation. Conclusions. Potential soil infestation by seeds of Giant sumpweed in ruderal biotopes since 2009 increased by 2.0—2.7 times, and in crops of cultivated plants — by 4.7—12.1 times and reached 25.0—85.0 and 14.5—15.5 pcs./ m2 thousand, respectively. Seed germination of Giant sumpweed occurred only in spring and early summer. The number of seedlings on ruderal areas reached 636—862 plants/m2, and in crops — 23—62 plants/m2. Effective control of Giant sumpweed on uncultivated lands was achieved by mowing weeds, in sowing of grain crops with leaf herbicides in the tillering phase, row crops — by pre-emergence and post-emergence harrowing in combination with inter-row cultivation.