The influence of photoselective plastic films as greenhouse cover on sweet pepper yield and on insect pest levels

The behaviour of different types of photoselective plastic films was studied in a sweet pepper crop under a Kyoto type tunnel-greenhouse. The film' evolution of light properties, sweet pepper yield and the population size of whiteflies (Trialeurodes vaporariorum and Bemisia tabaci) and western flower thrips (Frankliniella occidentalis) were determined. The following films were tested: UV-absorbing white thermic PE, UV-absorbing blue coextruded three layer, UV-absorbing white coextruded three layer and yellow thermic PE. UV-nonabsorbing white thermic PE film was used as film control. All the films were 200¿ thick. The measurement of light properties after a year's cultivation showed increased of transmission within the UV wave length in the UV-absorbing white film and a reduction of PAR transmission in the blue coextruded three layer film due to dust accumulation. The greatest early and final commercial yield was obtained in a tunnel-greenhouse covered with the white coextruded three layer film and the smallest with the UV-absorbing white thermic PE film. The maximum population of thrips and, consequently, the greatest incidence of TSWV, were observed in the tunnel-greenhouses covered with white thermic PE film (control). The lowest population of thrips was observed under UV-absorbing white coextruded three layer film. The greatest population of whiteflies was obserbed in the control tunnel-greenhouse, while the lowest population was recorded under the UV-absorbing white thermic PE film. The behaviour of the films will be contrasted with the results of the second year of cultivation.