Effect of Water Hardness on the Mixture of Nicosulforun and 2,4-D Herbicides Performance on Velvetleaf (Abutilon theopharesti) Control

Water is the primary carrier for herbicide applications (it usually makes up about 99% of the spray solution) and deliver them to the target weeds that they are intended to control. The quality of water available for spraying will depend on the source of the water on the vineyard, eg. dam or channel. Many chemical elements can be dissolved in water but six major ions make up the dissolved material in most water: Calcium (Ca++), Magnesium (Mg++), Sodium (Na+), Sulfate (SO4-), Chloride (Cl-), and Bicarbonate (HCO3-). Hard water becomes “hard” because of the presence of carbonates, sulfates, and chlorides of calcium, magnesium, and iron. Water containing calcium and magnesium can reduce the effectiveness of post-emergence herbicides that are weak acids include glyphosate (Roundup), paraquat (Gramaxone), bentazon (Basagran), clethodim (Envoy), sethoxydim (Poast), nicosulforun (Cruise) and 2,4-D (many products).Nicosulfuron is a post-emergence sulfonylurea herbicide that act through inhibition of acetolactate synthase (ALS) and controls many difficult-to-manage monocotyledonous weeds at low rates in corn. Also, 2,4-D is a selective herbicide from the group of auxin-like herbicides that act systematically to control broadleaf weeds in cereals. "Mixing herbicides" can be used to reduce the effect of hardness factors in the water carrying herbicides. The purpose of a good mix is to increase the effect of the compound on weeds without damaging the crop. The primary reasons that herbicides are mixed are to improve bioactivity and reduce costs. Therefore, the application of mixing reduces labor costs, the number of crossings across the farm, equipment depreciation, and mechanical damage to the crop and soil. Interactions of two herbicides can occur in three ways: each herbicide has an independent mode of action (additive effect); one herbicide reduces the action of another herbicide (antagonism), and one herbicide increases the presence of another herbicide (synergism). The question is whether the synergistic effects that occur in some conditions in the mixing of two herbicides can be used to reduce the negative effects of hard water on the performance of hard water sensitive herbicides? Therefore, this study was conducted to evaluate the effect of water hardness on the efficacy of nicosulfuron and 2,4-D tank mixing on the control of velvetleaf (Abutilon theophrastis Medicus.).

 The effect of mixing nicosulfuron (Cruse- OD4%) and 2,4-D amine (U46- SL72%) herbicides on velvetleaf (Abutilon theophrastis Medicus.) weed control in the presence of hard agents carried out as factorial arrangement based on randomized complete block design with three replications at the Research Greenhouse of Ferdowsi University of Mashhad in 2019. The first factor of water hardness applied in four levels including deionized water (non-hard), 0.1 M concentrations of CaCl2, MgCl2, FeCl3 salts (Merck, Darmstadt, Germany). The second factor was mixing nicosulfuron and 2,4-D amine herbicides as 6.25, 12.5, 25, 50 and 100% of the recommended dose. The mixing ratios were (0:100), (25:75), (50:50), (75:25) and (100: 0). In addition, 10 pots were considered as control without spraying.Velvetleaf seeds were collected from a heavily infested corn fields in Mashhad, Khorasan Razavi province in northeastern part of Iran. To obtain uniform seedlings, seeds were treated by sulfuric acid 98% during 1 min. Seven seeds pre-germinated in petri dishes were transplanted at 1 cm deep in 1 L plastic pots in a mixture of soil, sand and cocopeat (1 : 1 : 1 wt ⁄ wt ⁄ wt) containing all necessary macro- and micronutrients. The pots were kept in a greenhouse at natural daylength and a temperature around 25°C during the day. The pots were sub-irrigated daily. Prior to herbicide application, plants were thinned to five uniformly sized plants per pot.The herbicide solutions were applied at the 3-4 leaf stage of the weed using a cabinet sprayer equipped with a flat fan nozzle (No.11004) delivering a spray volume of 390 Lha-1. A four-parameter log-logistic model (equation 1) was fitted to the data using the open-source statistical software R 2.6.2 and the drc statistical addition package.   Y=c+[d-c ⁄ 1+exp[b(log x-log e)]]   (1)where Y is the response expressed as percentage of the untreated control, c and d are the responses at very high and very low herbicide rates, respectively, b is the slope of the curve around the point of inflection, and e  is the herbicide rate giving response halfway between d and c (=ED50). If c = 0, then the four-parameter model reduces to the three-parameter model (equation 2), with the lower limit being zero.   Y=d ⁄ 1+exp[b(log x - log e)] .

The results showed that the net effects of herbicides were affected by hard water factors such as calcium, magnesium and iron III chloride. Besides, their efficiency in controlling biomass, survival percentage and height of velvetleaf were decreased. The inhibitory effect of hardness factors on herbicide performance was different. Calcium chloride and magnesium chloride had the highest reduction effect on nicosulfuron and 2,4-D amine, respectively. Therefore, to reduce the effect of water hardness factors, two herbicides were evaluated by mixing. The results indicated that the type of effect on herbicide mixing in biomass control of velvetleaf was synergistic, and reduced antagonistic effect of water hardness factors. Equal proportions of both herbicides in reducing the effect of calcium chloride and iron III chlorides, high ratio of nicosulfuron in reducing the effect of magnesium chloride, had the best performance in controlling the biomass of velvetleaf. Therefore, depending on the salts involved in the water hardness of the sprayer tank, changing the mixing ratio of the two herbicides nicosulfuron and 2,4-D amine can be achieved the best performance control of velvetleaf.