Study of the effect of irrigation and nitrogen fertilizer on sugar beet growth and population dynamism of Empoasca decipiens (Hom.: Cicadellidae) and Thrips tabaci (Thys.: Thripidae)

To study of environmental effects on sugar beet traits, population dynamism of Empoasca decipiens and Thrips tabaci, effects of three irrigation regimes (irrigation after 70, 105 and 140 mm cumulative evaporation from class A pan) and three fertilizer levels (200, 150 and 100 kg/ha net nitrogen) were evaluated in a complete randomized block design with 4 replication. The results showed that percentage of water and protein content and dry weight of crop foliage were affected by irrigation regimes and fertilizer treatments and these changes influenced the population of the pests. Irrigation after 70 mm in comparison to 140 mm, increased percentage of the foliage water 78.6%, but its protein content decreased 31.1%. Increase of nitrogen fertilizer from 100 to 200 kg/ha, increased protein content 12.25%. The highest and lowest mean of the pest population were observed in 105 and 140 mm irrigation treatments respectively. Irrigation after 105 mm in comparison to 140 mm, increased population of leafhopper and thrips as much as 3.37 and 3.51 times respectively. Increase of nitrogen fertilizer from 100 to 200 kg/ha, increased population of leafhopper and thrips 37.5% and 48.66% respectively.