The effect of chemical weed control with reduced herbicide rates (pre-em., pre-em. + post-em., post-em.) on weed population density and maize yield was compared in three tillage systems (mouldboard, chisel, disk harrowing) for lessive pseudogleyic soil in north-eastern Croatia (1997Croatia ( -1999. These main weeds were present in all tillage variants:and Calystegia sepium (L.) R.Br. The density of all weeds was significantly affected by tillage and it ranged from 204 plants on untreated plots with mouldboard to 372 and 421 plants per m 2 with chisel ploughing and disk harrowing, respectively. In comparison with standard tank-mixture of atrazine herbicide (metolachlor 50% & atrazine 20%) at the recommended rate, atrazine-free herbicide combinations (metolachlor + 50% prosulfuron & 30% primisulfuron-methyl; sulcotrione + bromoxynil; thifensulfuron-methyl + nicosulfuron) showed a similar total efficacy of weed control (95-96%). Band spraying with standard treatment at a half-recommended rate combined with mechanical weed control brought a satisfactory total weed reduction (83-87%). The weed control methods had no effects on maize yields that were significantly affected by year and tillage. Compared to the highest yield with mouldboard ploughing (10.2 t/ha), average percent yield depressions with chisel ploughing and disk harrowing were 10 and 22%, respectively.

The aim of the study was to examine allelopathic effect of marigold (Calendula officinalis L.) on germination and growth parameters of weed species hoary cress (Cardaria draba (L.) Desv.). In total, four experiments were conducted. In Petri dishes, cogermination of hoary cress and marigold seeds, and extracts from fresh and dry marigold biomass in concentrations of 5 and 10% (50 and 100 g per litre of distilled water) were evaluated. In pots with soil, effect of extracts from fresh marigold biomass in aforementioned concentrations and effects of fresh and dry marigold residues in two rates (10 and 20 g/kg of soil) were examined. Cogermination of hoary cress and marigold seeds promoted germination and growth of weed. Extracts from fresh and dry marigold biomass, in Petri dish assay, reduced germination of hoary cress on average for 11.9 and 96.9%. Extracts from fresh biomass promoted shoot length of weed seedlings. On the other hand, extracts from dry biomass strongly inhibited all measured parameters. Higher concentration had greater inhibitory effect. Extracts from fresh marigold biomass applied in pots with soil, had stimulatory effect on weed growth, except for root growth which was inhibited with higher concentration (for 6.6%). Fresh marigold residues incorporated in soil had stimulatory effect on germination and seedling growth of hoary cress. Dry residues also had positive effect, but root length was inhibited for 15.4% with lower and 10.2% with higher rate.

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The effects of different tillage systems and dose reduction on the efficacy of triasulfuron & chlortoluron mixture in the post-emergence control of annual broad-leaved weeds in winter wheat and spring barley were studied on lessive pseudogley soil in north-eastern Croatia during 1997-2000. Total dry biomass production in untreated plots was significantly influenced by tillage and it was lowest in continuous mouldboard ploughing (99 kg/ha), medium and similar in mouldboard ploughing/disk harrowing alternating every second year and in chisel ploughing (218 kg/ha) whereas the biomass was highest in continuous disk harrowing (422 kg/ha). Thereby the proportion of annual broad-leaved weed biomass was 70, 63, and 28%, respectively. Chenopodium album L., Ambrosia artemisiifolia L., Ch. polyspermum L. and Polygonum aviculare L. are the most abundant annual weed species in all tillage treatments. One half and one quarter of the recommended rate decreased the control efficacy of total weed biomass by 12 and 19%, respectively in wheat and by 6 and 15%, respectively in barley compared to the highest dose but they still provided a very good biomass control of main annual weeds (94-96 percentage units). The efficacy of reduced herbicide doses in the control of annual broad-leaved weeds did not vary significantly between tillage treatments and growing seasons. Significant interaction with continuous disk harrowing tillage and one-quarter herbicide dose was detected in the last year of wheat trial when perennial weeds increased their biomass proportion 8 times compared to four years before.

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