Efficacy of thiencarbazone-methyl+isoxaflutole +cyprosulfamide as compared with common herbicides for weed control in corn (Zea mays L.))

Plant Protection Organization (PPO) has registered sixteen commercial herbicides formulations for weed control of corn in Iran (Nourbakhsh, 2016). Among these herbicides, eight herbicides contain one active ingredient and the other seven have two or three active ingredients including acetolactate synthase (ALS) enzyme inhibiting groups - similar-auxin groups, photosynthetic inhibitors of photosystem II and inhibitors of fatty acids and cell division, which are sometimes formulated with safeners. 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 (Hadizadeh, 2016). 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 corn production based on using new herbicides thiencarbazone + isoxaflutol + cyprosulfamide and comparing their efficacy with the common registered herbicides in the major corn growing areas of Iran.

A field study was conducted in four regions of Iran, including Mashhad, Karaj, Shiraz and Kermanshah during 2017 growing season. The statistical layout was a completely randomized block design with four replicates. Seven chemical treatments were mesotrione+ s-metalachlor+ terbuthylazine (Lumax® 537.5SE pre-emergence, 4 l ha-1 or post-emergence, 4.5 l ha-1), foramsulfuron+iodosulfuron+thiencarbazone (MaisTer Power® 4.25%OD, 1 l ha-1), topramezone (Clio® 29.7%SC, 150 ml ha-1) and the new herbicide thiencarbazone+isoxaflutol+cyprosulfamide with three recommended doses (Adengo 46.5%Sc, 330, 440 and 550 ml 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. Corn was harvested from 10 m2 of each plot after removing border plots. Corn grain yield was determined after adjusting the moisture level of grain to 14 %. To measure corn biological yield, samples of 10 corn plants were taken and then were dried in an oven. Data from each region were subjected to statistical analysis using SAS/STAT statistical software and the means were separated by LSD (α=5%).

The results showed a diverse spectrum of weeds (17 species) at the experimental locations. Pigweed species (Amaranthus retroflexus and A. blitoides) were dominant in all tested locations. The next dominant weed species were Portulaca oleraceae L., Echinochloa crus-galli (L.) P. Beauv., Convolvulus arvensis L., Chenopodium album L., Sorghum halepense (L.) Pers., Physalis divaricate L., Glycyrrhiza glabra L., and Setaria viridis L. Across the experimental locations, thiencarbazone+isoxaflutol+cyprosulfamide was efficient at 440 and 550 ml ha-1 concentrations for weed control (75 to 88%). However, when applied at dosage of 330 ml ha-1, its weed control efficiency was lower (30 to 50%). Topramezone was inefficient in controlling weeds in all the locations, which was in agreement with the findings of some previous studies (Hadizadeh et al. 2015). Foramsulfuron+Iodosulfuron+Thiencarbazone (1l ha-1) was efficient in weed control (70-85%) in Mashhad and Karaj. All herbicides (except topramezone) effectively controlled P. divaricate as an invasive weed. E. crus-galli and G. glabra were identified as difficult-to-control weeds. None of herbicides showed injury symptoms on corn.

Thiencarbazone+isoxaflutol (440 and 550 ml ha-1) showed 70-85 weed control efficiency averaged in the all experimental locations and it could be recommended to be used in corn field after registration process. Due to environmental concern, it should be applied at low doses. Foramsulfuron+ idosulfuron+ thiencarbazone was found to be the next efficient herbicide. Barnyard grass and licorice were difficult-to-control weed species or there were not controlled by new herbicides. We also suggest evaluation of the herbicides for their residual effects on the succeeding crops. Acknowledgements: We wish to thank Professor Eskandar Zand, Dr. Mehdi Minbashi, Dr. Saeed Khavari and Mr. Yahya Javid-Shafiee for their very useful contribution to this project.