Efficacy of Dicamba+ Mesotrione+ Nicosulfuron compared with common herbicides for weed control in corn (Zea mays L.)

Plant Protection Organization (PPO) has registered fourteen commercial herbicides formulations for weed control of corn in Iran (Nourbakhsh, 2021). Among these herbicides, eight herbicides contain one active ingredient and the other six 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. Weed species do not similarly respond to herbicides and previous studies showed some existing inherent tolerance, causes the percentage control of some of the weed species being lower than the others (Hadizadeh, 2016). 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 dicamba+ mesotrione+ nicosulfuron and comparing their efficacy with the common newly or some of older registered herbicides in the major corn growing areas of Iran.

A field study was conducted in four regions of Iran, including Mashhad, Ahwaz, Zarghan and Kermanshah during 2019 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 post-emergence, 4.5 l ha-1), nicosulfuron+rimsulfuron (Ultima® 75%WG, 175 g ha-1), topramezone (Clio® 29.7%SC, 150 ml ha-1), thiencarbazone+isoxaflutol+cyprosulfamide (Adengo® 46.5%Sc, 440 ml ha-1), and the new herbicide dicamba+mesotrione+nicosulfuron with five recommended doses (Calisto Solid 569.5 WG, 400, 500, 600, 700 and 800 g 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 (18 species) at the experimental locations. Pigweed species (Amaranthus spp.) were present in all tested locations but were not dominant in Ahwaz. The next dominant weed species were Portulaca oleraceae L. and Chenopodium album L. in Mashhad and Zarghan; Physalis divaricate L. in Ahwaz and Zarghan, Convolvulus arvensis L., Echinochloa crus-galli (L.) P. Beauv., and Corchorus olitorius L. in Ahwaz; Hibiscus trionum L., in Mashhad; Glycyrrhiza glabra L. and Xanthium strumarium L. in Kermanshah and finally Sorghum halepense (L.) Pers., was dominant in Zarghan. Across the experimental locations, dicamba+mesotrione+nicosulfuron was efficient at 700-800 g ha-1 application doses for weed control (75 to 88%). However, when applied at dosage of under 700 gl ha-1, its weed control efficiency was lower (50 to 70%). Topramezone and nicosulfuron+rimsulfuron were inefficient in controlling weeds in all the locations. In contrast, thiencarbazone+isoxaflutol+cyprosulfamide was among the most efficient treatments wich these findings are in agreement with the results of some previous studies (Hadizadeh et al. 2015; Hadizadeh et al., 2020). E. crus-galli was identified as the most difficult-to-control weeds and G. glabra and P. oleraceae were the next ones. None of doses of new herbicide showed injury symptoms on corn.

Dicamba+mesotrione+nicosulfuron (700 and 800 g 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 could be applied at lower doses when difficult-to-control weeds were not present. Thiencarbazone+isoxaflutol+cyprosulfamide was found to be the high efficient herbicide. Barnyard grass, licorice and common purslane 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.