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

Abstract

Egyptian 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.

Simulating sulfosulfuron fate in soil under different weather scenarios to support weed management decisions

“…The degradation of sulfosulfuron in soils from these plots was analyzed in a previous work, showing significantly higher first-order degradation rate constant and activation energy in the soil from H. Eden (Table 1). 32 In the current study, the experimental plot at each site consisted of three beds, 1.93 m wide and 50 m long each. In H. Eden, sulfo- 17.…”

“…The temperature dependence (i. e. activation energy of degradation) was calculated from degradation experiments in a controlled environment (Table 1), described in a previous publication. 32 The Freuindlich sorption constant of sulfosulfuron (Kf) was estimated from soil pH, using the model proposed by Brown et al, and the Freundlich exponent was set as the average value (0.93) in the soils of that study. 17 Initial sulfosulfuron concentration (mass solute/volume soil) was set in each simulation according to the application scenario (see Sections 2.1 and 2.4).…”

“…This time frame represents the start of Egyptian broomrape germination (after transplanting) and the beginning of its seedlings attachments to tomato roots (200 growing-degree days). 39 Finally, the critical concentration of sulfosulfuron was determined based on its dose-response curve, reported by Paporisch et al 32 The half maximal effective concentration (EC 50 ) value (23.6 ng g −1 )which is the sulfosulfuron concentration that caused a 50% reduction in biomass of Egyptian broomrape when parasitizing tomatowas set as the critical concentration for control. It was observed that at this concentration the biomass of Egyptian broomrape is mostly represented by new attachments of broomrape, prior to differentiation of a Figure 1.…”

“…To evaluate the impact of the earlier-mentioned variation in sulfosulfuron fate on control efficiency of Egyptian broomrape in tomato, the simulation results were compared to previously determined EC 50 (23.6 ng g −1 ) when parasitizing tomato. 32 In H.…”

“…30,31 However, in a recent study we demonstrated that the variation between such soils in sulfosulfuron degradation rate, coupled with application timing before planting, could influence Egyptian broomrape control efficacy. 32 Furthermore, due to the relatively high leaching potential of sulfosulfuron, 11 application that is followed by a high amount of precipitation could result in increased leaching that might further reduce control efficacy. Thus, the main goal of the current study was to evaluate the fate of sulfosulfuron in soil between pre-planting incorporation and tomato transplanting, under variable weather scenarios.…”