In 2019, we conducted an experiment in a field planted with onions. We wanted to study the effect of five different biostimulants on the occurrence of pests and the yield of onion. Biostimulants Vitanica Si, Vitanica MC, Vitanica RZ and Basfoliar contain the seaweed Ecklonia maxima, which affect the resistance of plants to various stressors. Vitanica RZ also contains the bacterium Bacillus amyloliquefaciens, which allow better nutrient uptake. Biostimulant Plantonic contains extracts of various plants. We studied the influence of biostimulants on the occurrence of injuries due to onion thrips (Thrips tabaci), onion fly (Delia antiqua) and click beetles (Elateridae), on occurrence of infection with onion downy mildew (Peronospora destructor) and on the yield of onions. The experiment took place in the Laboratory Field of the Biotechnical Faculty in Ljubljana. Spraying with biostimulants took place at 7- or 14-day intervals. We found the effect of the biostimulant Basfoliar on the minor occurrence of downy mildew and the same effect of Plantonic on the occurrence of click beetles. We found that biostimulants had no effect on the occurrence of onion thrips. The highest yield of onions was determined using the biostimulants Vitanica Si and Vitanica MC using 70% concentration of insecticides and fungicides; more than 13 t/ha and the lowest yield was in negative control, less than 6 t/ha. The highest number of healthy bulbs was found in the treatment of 100% insecticide + Plantonic, around 83% and the smallest in the treatment of 70% insecticide + 70% fungicide + Vitanica RZ, around 39%.
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