Efficacy of Fluroxypyr Compared with Common Broadleaf Herbicides in the Wheat Fields

Plant Protection Organization (PPO) has registered 22 commercial herbicides formulations for weed control of wheat, barley and triticale in Iran. Among these herbicides, sixtheen herbicides introduced act as two proposed or only for broadleaved weeds. Their active ingredients including acetolactate synthase (ALS) enzyme inhibiting groups, synthetic-auxin groups,a photosynthetic inhibitor of photosystem II, and pigment synthesis inhibitor groups (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 tolerant to herbicides or may be developing resistant to one mode of action. Thus, we need new herbicides to suppress such weeds. The aim of this work was to find the best chemical treatments against weeds in wheat production based on using the new herbicide fluroxypyr and comparing their efficacy with commonly registered herbicides in the major wheat growing areas of Iran.

A field study was conducted in four regions of Iran, including Karaj, Shahryar, Ahwaz, Shiraz, and Gonbad during 2017-2018 growing season. The statistical layout was a completely randomized block design with four replicates. Ten herbicides in 12 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), Bromoxynil + 2,4-D (Buctrile Univeral® 56% EC 1.5 L ha-1), Dichloprop+bentazone (Basagran DP 56.6% SL, 2 L ha-1) and the new herbicide Fluroxypyr with th recommended doses (Kavin Flurox® 20% EC 1.5, 2 and 2.5 L ha-1). 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%).

The results showed a diverse spectrum of weeds (14 species) at the experimental locations. Descuriania Sophia was dominant in two tested locations Karaj and Shiraz. The next dominant weed species were Galium aparine L., Conringia orientali and Centaurea depressa M.B. were present dominantly in Shiraz. Polygonum aviculare, Fumaria vailantii and Veronica persica were present in Karaj. Lepyrodiclis holosteoides as a noxious weeds, were dominant only in Shahryar. Malva neglecta and Scorpiurus muricatus were in Ahwaz and Bifora testiculata was dominat in Gnbad. Across the experimental locations, fluroxypyr was efficient at 2-2.5 L ha-1 concentrations for weed control (85.77 to 90.68%). However, when applied at dosage of 1.5 L ha-1, total weed control efficiency was lower (80.75%). Bromoxynil + 2,4-D (85.43%) , Dichloprop-p + Bentazon (83.98%) were the most efficient after fluroxypyr. Mecoprop-p + Dichloprop-p + MCPA and Bromoxynil + MCPA with 80% average efficiency controled weeds in all the locations. Triasulfuron + Dicamba and 2,4-D + Dicamba were inefficient in weed control (67.75 and 68.22% , respectively) across all locations. These findings were in agreement with the results of some previous studies (Minbashi and Saeedi, 2019, Minbashi et al. 2020). Lepyrodiclis holosteoides with average control of 63.68% and CV= 23.98% was the most difficult-to-control weed in this experiment. Other weeds beside that were Scorpiurus muricatus, Polygonum aviculare, Malva neglecta and Bifora testiculata identified as difficult-to-control weeds. None of herbicides showed visual injury symptoms on wheat.

According to these experiments, we found that the Fluroxypyr (2-2.5 L ha-1) 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 for non-difficult-to-control weeds. We found that Bromoxynil + 2,4-D was the most efficient next herbicide after fluroxypyr and Triasulfuron + Dicamba as an unefficient herbicide overall. L. holosteoides as the most hard-to-control weed was controlled only by upper dose (2.5 L ha-1) of new herbicide. Other difficult-to-control weed species were Scorpiurus muricatus, Polygonum aviculare, Malva neglecta and Bifora testiculata.