Wild poinsettia biology and management – determining optimal control with herbicides and propane flaming

Wild poinsettia (Euphorbia heterophylla L.) is a troublesome weed in irrigated summer crops and orchards. Data regarding the optimal herbicide rates for control of this weed, the impact of phenology on control efficacy, and non-chemical control methods for this weed are scarce. The objectives of this study were to: conduct dose-response analyses for trifloxysulfuron at 0–11.2 g a. i. ha⁻¹, glyphosate at 0–2880 g a. i. ha⁻¹, glufosinate-ammonium at 0–1600 g a. i. ha⁻¹ and propane flaming at 0–83 kg ha⁻¹ on wild poinsettia at 4-leaf, 8-leaf and flowering stages; evaluate the long-term control efficacy of these treatments; and link these finding to physiological models. Petri dish and pot experiments examined the germination and phenology of wild poinsettia. The calculated base temperature was 11.4 °C, and physiological time and wild poinsettia fresh weight and leaf number were strongly correlated, with R² values of 0.96 and 0.97, respectively. Wild poinsettia phenology had a crucial impact on herbicide efficacy. At the 4-leaf stage, all herbicide treatments were effective within the recommended rates with ED₉₀ values of 3.2, 698 and 206 g a. i. ha⁻¹ for trifloxysulfuron, glyphosate and glufosinate-ammonium, respectively. As the weed matured, it was less susceptible to these treatments. At the 8-leaf stage, only glyphosate and glufosinate-ammonium achieved an ED₉₀ within their recommended rates. The efficacy of flaming on wild poinsettia control was high at the 4-leaf stage with a control level of 95%, compared to only 31% and 13% at the 8-leaf and flowering stages, respectively. The long-term study revealed that for the 8-leaf application, the high glyphosate rate (1440 g a. i. ha⁻¹) was the only effective treatment, with 95% fresh weight reduction and complete flowering inhibition. This study promotes optimal herbicide applications and demonstrates the potential use of propane flaming for effective wild poinsettia control. The integration of data regarding optimal control with a phenology model offers an efficient tool to improve wild poinsettia management.