عنوان مقاله [English]
Introduction: Plant Protection Organization (PPO) has registered seventeen commercial herbicides formulations for broadleaved weed control of wheat in Iran (Nourbakhsh, 2019). Among these herbicides, five herbicides contain one active ingredient and the others have two or three active ingredients including acetolactate synthase (ALS) enzyme inhibiting groups, synthetic-auxin groups, photosynthetic inhibitor of photosystem II, and pigment synthesis inhibitor groups, which are sometimes formulated with safeners (Tomlin, 2009). Previous studies show that existing weed species do not similarly respond to herbicides and therefore the percentage control of some of the weed species is lower than the other species (Ohadi, 2010). These hard-to-control weeds are naturally resistant to herbicides. Thus, new herbicides with several active ingredients are suggested to be used to suppress such weeds. The aim of this work was to find the best chemical treatments against weeds in wheat production based on using new herbicides bromoxynil+2,4-D and comparing their efficacy with the common registered herbicides in the major wheat growing areas of Iran.
Material and Method: A field study was conducted in four regions of Iran, including Karaj, Shahryar, Kermanshah and Shiraz during 2017-2018 growing season. The statistical layout was a completely randomized block design with four replicates. Eight herbicides in 13 treatments were 2,4-D+MCPA (U46-Cambi fluid® 67.5%SL, 1.5 1 L ha-1), Mecoprop-p + Dichloprop-p + MCPA (Duplosan super® 60% SL , 1 L ha-1), Bromoxynil + MCPA (Bromicide® 40% EC, 1.5 L ha-1), Tribenuron-methyl (Granstar® 75% DF, 20 gr ha-1), Mesosulfuron-methyl + Iodosulfuron-methyl sodium+ Diflufenican+Mefenpyre-diethyl (Othello® 75% WG, 1.6 L ha-1), 2,4-D + Dicamba (Dialant super® 46.4 SL, 0.8 L ha-1), Triasulfuron + Dicamba (Lintur® 70% WG, 165 gr ha-1), and the new herbicide Bromoxynil + 2,4-D with six recommended doses (Buctrile Univeral® 56% EC, 0.75, 1,1.25, 1.5, 1.75 and 2 L ha-1). A hand-weeded treatment and an unweeded treatment served as controls. Weed density and weed dry weight for each plot were measured four weeks after the last application the herbicides. Wheat was harvested from six m2 of each plot after removing border plots. Wheat grain yield was determined after adjusting the moisture level of grain to 14 %. Data from each region were subjected to statistical analysis using SAS/STAT® statistical software and the means were separated by Duncan (α=5%).
Results and Discussion: The results showed a diverse spectrum of weeds (18 species) at the experimental locations. Descuriania Sophia was dominant in three tested locations except Kermanshah. The next dominant weed species were Galium aparine L. and Centaurea depressa M.B. were present dominantly in Kermanshah and Shiraz. Lepyrodiclis holosteoides and Convolvulus arvensis as noxious weeds, respectively were dominant in Shahryar and Kermanashah. Malcolmia africana and Sinapis arvensis were present in Karaj. Across the experimental locations, Bromoxynil + 2,4-D was efficient at 1.5-2 L ha-1 concentrations for total weed control (85.7 to 91.47%). However, when applied at dosage of under 1.5 L ha-1, its weed control efficiency was lower (63 to 80%). Mecoprop-p + Dichloprop-p + MCPA and Bromoxynil + MCPA with 82% average efficiency in controlling weeds in all the locations, which was in agreement with the findings of some previous studies (Minbashi and Saeedi, 2019). 2,4-D + Dicamba and Triasulfuron + Dicamba were inefficient in weed control (68-72%) across all locations. Bromoxynil + 2,4-D (1.5 L ha-1 and upper doses), Mecoprop-p + Dichloprop-p + MCPA, and Bromoxynil + MCPA were the most efficient to control Lepyrodiclis holosteoides with 86.99 to 99.19% of weed density.This weed beside C. arvensis and G. aparine were identified as difficult-to-control weeds. None of herbicides showed visual injury symptoms on wheat.
Conclusion: According to these experiments, we found that the Bromoxynil + 2,4-D (1.5 L ha-1 and upper doses) as new candidate herbicide showed good to excellent (85%-100%) weed control efficiency averaged in the all experimental locations and it could be recommended to be used in wheat field after registration process. Due to environmental concern, it should be applied at lower doses. Mecoprop-p + Dichloprop-p + MCPA and Bromoxynil + MCPA were found to be the next two efficient herbicides. C. arvensis, was the most difficult-to-control weed that there was not controlled by new herbicides. L. holosteoides and G. aparine were difficult-to-control weed species.