The effect of chlorpyrifos on flower and fruit development in grapefruit, Citrus paradisi Macfayden

Abstract

Deformations consisting of longitudinal ridges in the rind of Citrus fruits have recently been found in Southern California Citrus groves. Here, we report the correlation between ridge formation and applications of chlorpyrifos (Lorsban, Dow Chemical Company, Midland, MI) during the ‘feather-growth’ stage of bud break when flower buds become visible. All chlorpyrifos formulations resulted in significant ridging. The addition of agricultural oil and 2,4-dichlorophenoxyacetic acid (2,4-D) to chlorpyrifos resulted in the greatest ridging damage, and widened the window of susceptibility by 2 weeks in 1988. In 1989, no significant difference was seen between treatments of chlorpyrifos, although all were significantly greater than the control. The susceptible stages of bud growth are described, as are the non-susceptible stages which precede and follow it. Floral buds in which organs are just initiating are susceptible to fruit ridging upon application of chlorpyrifos. These ridges are the result of an increase in cell size of the flavedo tissue. A degree-day model which can be used to predict the timing of the susceptible stages is described.