The joint action of glyphosate, clethodim, and imazethapyr to control cogongrass (Imperata cylinderica L. Beauv) in the margin of the irrigation canals (A case study using two different approaches)

Abstract

Cogongrass (Imperata cylinderica L. Beauv) is a cosmopolitan invasive weed which may impact the ecological and economic integrity of our agro-ecosystems. In order to the optimum control of cogongrass and prevent the production of possible herbicide-resistant species, the use of glyphosate with selective herbicides can be considered as an important strategie in modern weed management programs. Therefore, two field experiments were performed to determine the joint action of glyphosate, clethodim, and imazethapyr using the additive dose model (ADM) as a reference model, based on a randomized complete block factorial design with 50 treatments and three replications on the margin of the irrigation canals in North Khuzestan Sugarcane Cultivation and Industry Company in 2021–2022. The treatments included five pure and mixed doses of the herbicides at five mixing ratios as 0:100, 25:75, 50:50, 75:25, and 100:0. The results showed that the different responses of herbicides binary mixtures were affected by various factors, such as the weed species and the physicochemical incompatibilities of the herbicide formulation. According to the results, the mixture of glyphosate:clethodim, followed the Hewlett model and synergized cogongrass control. While, the concentration addition (CA) model had a better fit for glyphosate:imazethapyr, i.e. showed additive effect. According to the visual observations, the herbicides used doses were reduced at the 4-6-leaf stage of cogongrass. The mixture of glyphosate:clethodim controlled about 90% of cogongrass at different ratios, while more than 81% control of cogongrass was achieved by mixing glyphosate:imazethapyr. Therefore, it concluded that we could combin glyphosate:clethodim and/or imazethapyr to control cogongrass without causing any antagonistic effect on each other's efficiency. On the other hand, the combonation of glyphosate, clethodim, and imazethapyr allows long-term control of broad-range cogongrass and delays in the resistance in the margin of irrigation canals.