Phytosanitary State of Walnut (Juglans Regia L.) in the Green Plantings of the Dnipro Сity

Abstract

Walnut is a promising element of the greening system of the Ukraine urbanized landscapes due to its resistance to environmental pollution, durability, fast growth, fruit qualities, etc. The aesthetic value and health-improving functions of Juglans regia trees in the city can be significantly weakened due to the destruction of the leaves by arthropod phyllophages and diseases. In the presented work, an analysis of the phytosanitary status of J. regia trees in green areas of Dnipro was carried out, the main leaf diseases were determined, a complex of insects and mites – phyllobionts of walnut trees, was established, and the level of their harmfulness was assessed. The research was conducted during the growing season of 2021 once a decade on 12 experimental sites, which differed in the conditions growth of J. regia trees growth. The study object was the walnut leaves and unripe fruits. 75 J. regia trees were examined. On average the damage degree to J. regia trees leaves by diseases is 46.9 %. The damage level by brown spot is 8.3 times higher than the similar indicator for white mould. The influence of anthracnose causative agent (Marssonina juglandis) often extends to walnut green fruits. The overall level of leaf damage by arthropod phyllophagous is 79.6 %. Among the types of damage are dominate the change in the leaves color due to sucking insects feeding (58.5 %) and gall-formation (53.8 %) as a result of the gall mites (Aceria erinea, A. tristriata) vital activity. The walnut arthropod phyllobionts taxonomic composition in the green areas of Dnipro city was determined. 16 species in 11 families and 4 orders were identified. The share of Hemiptera is 62.5 %, Lepidoptera – 18.8 %, Trombidiformes – 12.5 %, Thysanoptera – 6.2 %. Six species of entomophages were also identified. Two especially dangerous invasive species – Metcalfa pruinosa and Halyomorpha halys, were found on J. regia trees in some plots of the Dnipro city right bank territory. The most common and harmful species are the following: Aceria erinea, A. tristriata, Panaphis juglandis, Caloptilia roscipennella; potentially threatening – Halyomorpha halys, Metcalfa pruinosa.