Impact of western flower thrips on growth, photosynthesis and productivity of greenhouse cucumber

Abstract

Low, medium and high densities of western flower thrips ( Frankliniella occidentalis (Pergande)) were established in three greenhouses in 1996 and 1998 to investigate effects of thrips on growth, photosynthesis, yield and quality of greenhouse cucumber. Cucumber fruit were very susceptible to direct cosmetic damage by western flower thrips (WFT). High densities of WFT for short time periods significantly increased the number of fruit downgraded from grade #1 to #2. The most vulnerable stage to cosmetic damage was 4–10 days before fruit harvest, when the fruit were growing rapidly. WFT also increased fruit curvature and reduced plant growth, photosynthesis and marketable fruit yield. However, the impact of WFT on plant growth, photosynthesis and marketable yield was mainly cumulative; the impact was less dependent on the density or exposure duration alone, but more on thrips abundance (integration of thrips density over time). Leaf growth, leaf photosynthetic rate, marketable yield were reduced when plants were exposed to more than 700–2000, 2800, 3000 accumulated thrips-days per sticky card, respectively. It was very difficult for cucumber plants to recover from thrips damage once yield loss had taken place. Therefore, it is recommended to control thrips abundance below 700 accumulated thrips-days per sticky card to prevent a negative thrips impact on plant physiology or yield. The impact of WFT on fruit curvature was smaller than on fruit appearance, but more serious than on plant growth and yield. Five-hundred accumulated thrips-days per sticky card would significantly increase fruit curvature. The implications of experimental results from this study for WFT control are discussed.