This study investigated the impact of climate variability on pigweed (Amaranthus spp.) management in processing tomato (Solanum lycopersicum) fields across northern Israel, which span a climate gradient from semiarid to Mediterranean conditions. Conducted over two consecutive growing seasons (2020-2021), the research aimed to optimize weed management recommendations on a regional scale. The main objectives were to assess treatment timing and intensity and evaluate the efficacy of integrated weed management (IWM) in reducing reliance on herbicides. In 2020, standard chemical treatments-a tank-mix application of metribuzin (175 g a.i. ha-1) and rimsulfuron (25 g a.i. ha-1)-were applied in six field experiments based on cumulative growing degree days (GDD) to account for climate variability among sites. An infestation index was developed to represent the initial state of the fields and the magnitude of the change in infestation. In 2021, IWM was introduced, combining finger weeder cultivation with herbicide treatments at three sites. Results from the first season showed that in early-plantings, a single herbicide application at 150 GDD was as effective as dual applications at 150 and 300 GDD. However, in late plantings, a single application at 300 GDD was ineffective. In the second season, all treatments effectively reduced Amaranthus infestation, with IWM performing comparably to herbicide alone. Importantly, IWM demonstrated the potential to control herbicide-resistant biotypes while minimizing chemical use, making it an environmentally sustainable option. This study underscores the importance of optimized application timing for minimizing unnecessary chemical treatments, offering valuable insights for growers facing future climate challenges.