Monitoring of the two spotted spider mite (Tetranychus urticae Koch) conducted in 2019–2021 in contract crops on sugar beet and on experimental plots

The two-spotted spider mite (Tetranyus urticae Koch) is a polyphagic pest of various crops. The consequence of its feeding on sugar beet leaves is the disturbance of photosynthesis and, as a result, inhibition of plant growth and development and a decrease in the sugar content in the roots. In the climatic conditions of Poland, the number of generations of the spider mite in the growing season may be from 4 to 6. The aim of the field research was at assessing the degree of threat to sugar beet plantations by the spider mite throughout the country as part of the monitoring carried out in 2019–2021, in terms of mite harmfulness. In total, in the years of the research, 241 plantations located in 15 voivodeships were inspected. In 2019, 4 land district were tested, in 2020 – 22 and in 2021 – 73 land district, respectively. The degree of infestation of the plantation (adult forms of mites) was classified into four groups. They were distinguished due to the number of pests, the area of occurrence, intensity of leaf discoloration and deformation, and the general condition of plants. During the three-year monitoring study, the most numerous were spider mites in the first degree of infestation of the plantation, i.e. ”poorly populate”.