No 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.

Accelerated microbial degradation following previous repeated applications of the same pesticide, or another pesticide of a similar chemical structure, is a known phenomenon. Currently there is limited information regarding accelerated degradation of sulfonylurea (SU) herbicides. This study is aimed to evaluate the effect of repeated SU applications on the degradation rate of the SU herbicide sulfosulfuron in soil. The effect of repeated applications of sulfosulfuron on its degradation was assessed in two soils, using a sorghum root elongation bioassay. The effect of consecutive applications of sulfonylurea herbicides over the course of three to four seasons was further examined in controlled environment and a field study. Degradation of sulfosulfuron was determined following its application to soil samples from the field or a controlled environment, by measuring sulfosulfuron residues using liquid chromatography-tandem mass spectrometry. Following the repeated application of sulfosulfuron in the bioassay, the time to reduce sorghum root growth by 50% was shortened by up to 31.6%. However, consecutive application of SUs in the controlled environment had no effect on sulfosulfuron degradation rate constant. Yet, sulfosulfuron degradation rate was enhanced by a factor of 1.35 following consecutive application of SUs in the field, compared to untreated control soil. The data confirm that sulfosulfuron degradation could be enhanced due to repeated sulfosulfuron applications, thus potentially reducing its herbicidal efficacy.

Nutrient availability to plants is a key factor in plant productivity (Fisher et al., 2012). While insufficient nutrient availability is a major agronomic problem in some regions, in other parts of the world the increasing inputs of fertilizers and organic waste products, to meet the plant nutritional demands in intensive agriculture, has resulted in excess input of nutrients (Foley et al., 2011). Consequently, agriculture production costs, energy costs and nutrient pollution is enhanced. While new technologies allow precision delivery of nutrients to crops only when and where they are required (Hedley, 2015), this approach requires a thorough understanding of the mechanisms involved in root nutrient uptake. To meet the challenge of precision nutrient inputs to crops, a thorough understanding of the mechanisms involved in root nutrient uptake and