Weed problems, challenges, and opportunities in Iran.
Weeds are a serious threat to crop production in Iran as they reduce the yield of wheat, barley, rice, maize, and chickpea on average by 23%, 21%, 35%, 20%, and 50%, respectively. Orobanche spp., Avena ludoviciana (Durieu.), Convolvulus arvensis (L.), Sorghum halpence (L.) Pers, and Cuscuta compestris (Y.) are the most important weed species that compete with major crops in Iran. Recently, some newly introduced and invasive weeds, including Hordeum spontaneum (K. Koch.), Cynanchum acutum (L.), Physalis divaricata (L.), and Azolla filiculoides (Lam.), have become a very serious problem in a wide range of crops in different parts of Iran. Chemical control is the predominant weed management practice in Iran. In addition, mechanical weed control methods including soil tillage and hand weeding are applied to a lesser extent. 2,4-D + MCPA (in cereal crops), clodinafop-propargyl (in wheat crop), haloxyfop-r-methyl ester (in broadleaved crops), tribenuron-methyl (in wheat), nicosulfuron (in maize), trifluralin (in oil crops), metribuzin (in potato), glyphosate (in orchards and non-cultivated areas), and paraquat (in waste lands and between crop rows) are the most commonly used herbicides in Iran. There are currently 14 unique cases (species x site of action) of herbicide-resistant weeds in Iran. The most important and newly emerged challenges in Iran are to manage the present noxious and invasive weed species. Increasingly, the evolution of herbicide-resistant biotypes in wheat and other important crops would be another challenge in the future. In addition, the adoption and extension of integrated weed management strategy, addition of suitable adjuvants to herbicide tank mixture, and use of proper sprayers would remain critical challenges in weed management practices in Iran. The integration of weed control methods such as crop rotation, tillage, planting date and pattern, herbicides, and allelopathy would lead to the effective and sustainable management of weeds.