Application Timing and Degradation Rate of Sulfosulfuron in Soil Co-affect Control Efficacy of Egyptian broomrape (Phelipanche aegyptiaca) in Tomato

Abstract

AbstractEgyptian broomrape (Phelipanche aegyptiacaPers.) is a root-parasitic weed that severely damages many crops worldwide, including tomato (Solanum lycopersicumL.). In Israel, the management protocol used forP. aegyptiacain open-field tomato includes PPI sulfosulfuron at 37.5 g ai ha−1to the top 10-cm soil layer. The objective of this study was to investigate the co-effect of sulfosulfuron application timing and variable degradation rate in soil on the control efficacy ofP. aegyptiacain tomato. Degradation of sulfosulfuron (80ng g−1soil) at a temperature of 15C, measured in soil samples from three farms using liquid chromatography–tandem mass spectrometry, followed a first-order kinetics with variable degradation rate constant among sites (0.008 to 0.012 d−1). Incubation at 25 C increased sulfosulfuron degradation rate constant by a factor of 2 to 2.7 in soils from the different sites, with a similar degradation rate order among soils. A higher degradation rate in the soil resulted in a shorter period of residual activity, measured using a sorghum [Sorghum bicolor(L.) Moench.] bioassay.Phelipanche aegyptiacamanagement in open-field tomatoes was investigated in five independent field experiments. Sulfosulfuron soil concentration throughout the growing season (following preplant incorporation of 37.5 g ha−1) was calculated from laboratory-measured degradation rates, which were corrected to represent the effect of recorded temperatures at each field. At the end of the tomato growing season, control efficacy ofP. aegyptiacavaried among experiments (70.4% to 100%) and positively correlated with predicted sulfosulfuron concentration at the critical period for seedling control (R2=0.67). The current study confirms that sulfosulfuron is degraded in soil to nonphytotoxic metabolites and that rapid degradation rates would result in reduced injury toP. aegyptiacaseedling and, consequently, lower control efficacy.