No abstract

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.

The aim of the research was to determine the effectiveness of various methods for breaking seed dormancy of weed species Johnson grass (Sorghum halepense (L.) Pers.) and their influence on germination and seedlings growth. Beside control treatment, eight treatments for breaking dormancy of seeds were applied: seed immersion in distilled water for 24 hours; seed immersion in water at 60 °C for 1 hour; immersion in a 0.2% solution of potassium nitrate for 24 hours; immersion in 2% solution of sodium hypochlorite for 8 hours; treatments with concentrated sulphuric acid for 5 and 10 minutes; treatment with concentrated sulphuric acid for 5 minutes and germination in darkness; and combined treatment of sulphuric acid (5 minutes) and 1.5% potassium nitrate solution (2 hours). Average germination of Johnson grass seeds in control treatment was very low, only 2.8%. All dormancy breaking treatments increased seed germination and the highest germination was observed in treatment with combination of sulphuric acid and potassium nitrate (35.0%) and treatment with 2% sodium hypochlorite (30.6%). However, sodium hypochlorite reduced root length of seedlings for 40.9% compared to control, while all treatments had a positive effect on Johnson grass shoot length. Total seedlings length was the highest when seeds were treated for 5 minutes with sulphuric acid. None of the treatments showed significant effect on Johnson grass seedlings fresh weight. Seed germinated fastest in treatment with a combination of sulphuric acid and potassium nitrate (4.58 days), and slowest when seeds were immersed in water (8.16 days) and in the 2% solution of sodium hypochlorite (8.92 days).

Laboratory bioassay was carried out to study the insecticidal effect of 9 Croatian inert dusts against Sitophilus oryzae (L.) and to test their influence on bulk density of treated wheat. In order to compare effectiveness of Croatian inert dust samples, a standard USA diatomaceous earth (DE) Celatom® Mn 51, registered as an insecticide for stored-products protection, was used. Wheat kernels with approximately 13% moisture content were treated with inert dusts at doses 300, 400, 500 and 600 ppm and mortality of S. oryzae adults was assessed after 7 and 14 days and progeny after 49 days. The most effective Croatian inert dust samples were D-02B, D-01 and MA-4 with the LD90 values of 359.6, 447.2 and 458.7 ppm, respectively. In addition, effective dose that reduced F1 progeny in half was lower in regard to the other tested samples including the standard DE Mn 51, with the ED50 values 71.9, 54.6 and 137.6 ppm, respectively. According to the XRF analytical results, the highest amount of biogenic silica (BSi) was found in samples D-02B, D-01 and MA-4 (45.98, 35.09 and 21.28%, respectively). Paleontological data analysis confirmed diatoms species in only 5 samples of Croatian inert dusts (D-01, D-02B, PD-1, MA-4 and JU-1). All tested inert dusts affected reduction in bulk density of treated wheat at the LD90 concentrations, from 4.4 (D-02B) to 5.6 (JU-1) kg hL-1. More effective inert dusts at lower doses equally reduced bulk density as less effective inert dusts at much higher doses.

The aim of the study was to determine the influence of different methods on breaking seed dormancy of weed species velvetleaf (Abutilon theophrasti Medik.) and redroot pigweed (Amaranthus retroflexus L.). The influence of seed sowing depth on emergence and growth of weeds was also evaluated. The results showed that the best treatment for breaking seed dormancy of velvetleaf was immersion of seeds in hot water (60°C) for 1 hour, while immersion in distilled water and 0.2% KNO 3 solution had no significant effect. Seed germination of redroot pigweed was significantly increased in all treatments, however 2% KNO 3 solution and cold stratification at 5ºC for 12 days had the greatest effect. Treatments had different influence on mean germination time, seed germination dynamics and seedling length of weeds. The highest percentage of emerged velvetleaf seedlings was recorded when seeds were sown at 1 to 4 cm depths and ranged from 55.6 to 67.9%. With the increase of sowing depth the emergence percentage decreased, however one quarter and one fifth of the seedlings emerged from 7 and 9 cm depths. Both seedling length and fresh weight were greater at lower sowing depths. Emergence of redroot pigweed was not significantly influenced by sowing depth, however seedlings length and fresh weight were greater at 5 cm depth than at 1 cm.