The effect of sowing time on pest spreading in spring oilseed rape crop

Abstract

The field experiments were conducted at the Experimental Station of Aleksandras Stulginskis University in 2015–2017. The aim of the experiment was to evaluate the influence of sowing time on spreading of pests and diseases in spring oilseed rape crop. The first sowing occurred when soil reached physical maturity, the other sowing dates were every 5 days in 2015–2016 and every 7 days in 2017. In 2015, the sowing time did not have a significant effect on the distribution of Alternaria brassicae. Meteorological conditions strongly influenced the severity of the disease. The sowing date had a significant influence on the distribution of Verticillium dahliae: in the spring rape crop sown in May, the stems were damaged by 6.4%, less compared to the crop sown in April. In 2016–2017, the rape seedlings in the plots of the latest sowing were significantly more damaged compared with those of earlier sowing dates. In 2016, spreading of Verticillium longisporum significantly increased by 3.7 times in the crop of spring rape sown on 10 May compared to other sowing dates. In 2017, the spreading of Verticillium dahliae in spring rape crops was more influenced by a colder than usual vegetation period and an abundant rainfall than the sowing time. In 2015, the intensity of Phyllotreta spp. damage in the rape seedling period (BBCH 10-19) significantly increased by 2.7 times with the sowing date from 30 April to 20 May. The spreading of Meligethes aeneus was the least in the spring oilseed rape sown at the optimal time (30 April and 5 May). In 2016–2017, Phyllotreta spp. were more intensively spread in the crops sown in April, and rape seedlings were significantly more damaged. In 2016, Meligethes aeneus were most widely spread in the spring rape crop of the earliest sowing (4 October). A significant decrease in the number of pests was detected in the rape crops sown in May compared to that sown in April. In 2017, the highest number of Meligethes aeneus was evaluated in the rape crop sown on 2 June, significantly by 3.9 times more compared with that in the earlier sown crop and by 2.9 times in the crop sown one week later. It is believed that the other generation of Meligethes aeneus from winter rape crops went to the spring rape crops. In 2016, there was a very strong statistically significant correlation between the sum of positive temperatures for the 10-day period up to the sowing of rapeseed and the prevalence of Phyllotreta spp. in crops: r = 0.98, P ≤ 0.05, and the damage intensity of rape seedlings by Phyllotreta spp. of (BBCH 10-19): r = 0.92, P ≤ 0.05. The warmer the weather was before rape sowing, the more active Phyllotreta spp. were. In 2017, strong correlations were established between the number of Phyllotreta spp. and the intensity of crop damage by Phyllotreta spp. and the crop density 3 days after the emergence: r = –0.82, P ≤ 0.05; r = –0.89, P ≤ 0.01, and 7 days after the emergence of spring rape: r = –0.81, P ≤ 0.05; r = –0.88, P ≤ 0.01.