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Irrigation’s effect on the development of turnip moth in seeds of winter wheat and corn

Relevance of research. Irrigation is a precondition for stable production of agricultural products, especially in regions with insufficient and unsustainable moisture. Studies have shown that the application of irrigation provides a change in the structure, chemical composition of the soil, as well as affect its aeration. The result of artificial irrigation is a change in the intensity of physiological processes in plants, their biomass, species composition of weeds in agrocenoses. These factors further significantly affect the species and quantitative composition of the entomofauna of agrocenoses, including winter wheat and maize. The purpose of the study was to determine the effect of drip irrigation and sprinkling on phenological and biological features of turnip moth development. Therefore, one of the main tasks of the research is to determine the dependence of fluctuations in the number of phytophagus on the type of irrigation. Results of the research. It has been established that drip irrigation and sprinkling are effective measures of crops’ protection against damage and invasion caused by turnip moth. The most dangerous for maize plants is the turnip moth in the “caterpillar” stage of the I-II age of spring generation. Sprinkling irrigation during the period of mass egg’s deposition and the revival of caterpillars of turning moth contributes to a significant decrease (by 6,8-67,7%) in the share of this type of pest, compared to conditions without an irrigation. Corresponding results were also obtained from a study of the effect of the different irrigation types on oulema in winter wheat crops. That is, the amount of the indicated phytophage under irrigation conditions was less than 3–6 times compared with the control (without irrigation). It was proved that in the case of sprinkling, compared with the control (without irrigation), the number of caterpillars of younger ages L1-L2 over the years ranged from 0,2 to 6,2 sp./m 2 , while in the control the density was 3,3 – 14,5 sp./m 2 . It has been established that the caterpillars of turnip moth in conditions of high soil moisture are more susceptible to entomopathogenic species of entomophoric fungi Beauveria bassiana (Bals.) Vuill. and B. tenella (Delacr.). Minimal damage to the pest by the indicated pathogens was noted on the caterpillars of older ages L3-L4. Without an irrigation, the proportion of infected caterpillars was 2,2 – 0,5%, which is 1,6 – 2,4 times less than sprinkling, and 1,1 – 4,8 times drip irrigation. Crop irrigation also affects the distribution of the pests over the soil layers. In dry and loose soil in rainfed areas, larvae and pupae of turnip moth occur at a depth of 10-20 cm, while in moist, compacted soil of irrigated fields up to 5 cm. This makes them more accessible for destruction during cultivation and other surface treatments. Conclusions. In the conditions of the Dry Steppe of Ukraine the terms of the turnip moth occurrence varies by years, depending on the weather factors. On average, during the years of research, the occurrence of a dangerous stage of turnip moth’ development (caterpillars) was observed in the third decade of May - the second decade of June. Irrigation and drip irrigation are effective enough to reduce the density of the phytophage population. During the observation period, it is noted that irrigation of crops by the method of sprinkling is a significant factor in limiting the number of caterpillars of turnip moth. The reduction in the proportion of the pest relative to the conditions without irrigation was 6.8-67.7%. The caterpillars of the L1-L2 younger generations are more vulnerable to the effects of irrigation in maize crops. It is noted that irrigation maximally reduces the number of eggs of turnip moth and pests in the early stages of development. That is, clarification of the effects of irrigation on the development of biting scoops in maize agrobiocenoses in the Steppe Dry region allows to determine the degree of threat to crops, reduce the density of the phytophage population, as well as to plan and adjust the main measures of crop protection against these damage.