Evaluation Effect of Adjuvant on Mesosulfuron+Iodosulfuron Herbicide Performance on Littleseed Canarygrass Control

Introduction: Adjuvant application is one of the most important ways to increase herbicide efficacy and decrease environmental damaging effects of herbicides. In general, It has displayed that a very few of the spray droplets retained on the surface of leaf plants and the majority of them bounce off the leaf surface. Therefore, in spraying processes, adjuvant designed to enhance the absorbing, emulsifying, dispersing, spreading, sticking, wetting, or penetrating properties of pesticides. Adjuvant are most often used with herbicides to help a pesticide spread over a leaf surface and penetrate the waxy cuticle of a leaf or to penetrate through the small hairs present on a leaf surface. Surfactants and crop oils are two types of adjuvant that are used for increasing efficacy of herbicides. In many cases, significant increases have been observed in biological activity with the addition of surfactants or crop oils. For example, the performance of specific graminicides and some sulfonylureas is usually increased by the addition of tank-mix oils. It is generally accepted that the benefit of oils is related to their ability to increase the drying period of droplets during their fly time before their impact on the plants, to improve the spreading of the deposit on difficult-to-wet targets (mainly Graminaceae), to act as solubilizing agents, and above all to enhance the penetration of herbicides into the plants. Among commercially available adjuvants, emulsified vegetable oils have been shown to increase droplet retention and spreading, and enhance absorption and translocation of active ingredients. It has been reported that efficacy of atrazine, bentazone, phenmedipham and rimsulfuron on various weeds were increased by the addition of rapeseed oils to solution spray. Materials and Methods: In order to evaluate the effect of adjuvant concentrations on surface tension of aqueous solutions, an experiment was conducted as completely randomized design with 4 replications at 8 levels of adjuvants (0, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 (% v/v)). Moreover, the effects of surfactant and vegetable oil on the efficacy of mesosulfuron + iodosulfuron commercial mixture on littleseed canarygrass (Phalaris minor Retz.) were investigated under greenhouse conditions in Agriculture Faculty of Ferdowsi University of Mashhad. Greenhouse study was conducted in 6 concentration levels of mesosulfuron-methyl+idiosulfuron (0, 5.62, 11.25, 22.5, 33.75, and 45 g ai ha-1). This herbicide was applied alone and with these adjuvants including: (i) citogate (a nonionic surfactant), (ii) castor oil and (iii) rapeseed oil each one of them at two levels 0.1 and 0.2 %, the experiments were arranged in a completely randomize design with a factorial arrangement of treatments with four replications. Results and Discussion: When adjuvants alone were applied against littleseed canarygrass, none of them had not phytotoxic effect so that fresh weight and dry weight of plants did not decrease significantly as compared to the control. The results of lab experiment showed the lowest and highest surface tension belonged to Citogate and rapeseed oil, respectively. Also the results of greenhouse experiment indicated all adjuvant were able to increase the efficacy of mesosulfuron + iodosulfuron herbicide. Relatively potency (R) of dry weight increased with usage of Citogate surfactant, castor and rapeseed oils to 1.4, 1.35 and 1.13 respectively. The Citogate surfactant leads to the greatest enhancement of herbicide efficacy. The foliar activity of the tested herbicide enhanced with increasing adjuvant concentration from 0.1 to 0.2 (% v/v). According to the accessible information, surfactants (nonionic Citogate) are suitable for reduction surface tension. Previous studies showed that nonionic surfactant was too effective in decreasing surface tension of spray solution. Despite, it has been observed that vegetable-derived oils could not greatly decrease surface tension. For example, castor oil decreased surface tension of water from 73 to 71.5 mN/m. Whereas, nonionic surfactants can lower the surface tension of the spray solution to 33 to 34 mN/m. It seems that drop in surface tension by the citogate surfactant is considered sufficient to decrease the contact angle of spray solution proplets and makes an extension of droplet on leaf plant. Ultimately, spray droplet spread can be very important in obtaining the desired foliar coverage for contact pesticides and appears to play a role in moving the active ingredient to more absorption sites on the plant. Conclusion: Based on the results of this study; the following conclusions can be made: (1) the ranking of adjuvants to enhance the tested herbicides efficacy was alike this order: citogate > castor oil> rapeseed oil

The Effect of PSII Inhibitors on Kautsky Curve and Chlorophyll Fluorescence in Common Lambsquarters (Chenopodium album L.) and Common Purslane (Portulaca oleracea L.)

Introduction: Desmedipham + phenmedipham + ethofumesate, phenylcarbamates + benzofuranyl alkanesulfonate herbicides, is widely used for post-emergence broad-leaved weed control in sugar beet. Chloridazon, a pyridazinone herbicide, is used as a pre- and post- emergence herbicide in sugar beet. Desmedipham, phenmedipham and chloridazon, are photosystem II (PSII) inhibitors, their translocation via xylem are slow, mostly absorbed not only by roots, but also by foliage. Their mode of action is through the blocking of electron transfer between the primary and secondary quinones (QA and QB) of PSII by binding to the QB-binding site and accepting electrons from QA in the chloroplasts. Measures of changes to the chlorophyll fluorescence induction curve (Kautsky curve), is a rapid, non-invasive and simple method for monitoring the physiological status of the photosynthetic apparatus in the plant. There are three phases found on the O, J, I and P steps. These phases primarily point out photochemical events relevant to PSII. The three phases are described as follows: at the O-J phase complete reduction of the primary electron acceptor QA of PSII takes place from 50 μs to 2 ms, the J-I phase corresponds to electron transfer from QA to QB happens between 2 to 30 ms and the I-P phase corresponds to the release of fluorescence quenching by the oxidized plastoquinone pool taking place within 30-500 ms. Materials and Methods: In order to determine how exposure affects the fluorescence induction curve (Kautsky curve) and its parameters, two dose-response experiments carried out for chlorophyll fluorescence measuring. The treatments involved desmedipham + phenmedipham + ethofumesate at 0, 51.38, 102.75, 205.5, 308.25, 411, 616.5 and 822 g a.i. ha-1 and chloridazon at 0, 81.25, 162.5, 325, 650, 1300, 1950 and 2600 g a.i. ha-1 on common lambsquarters (Chenopodium album L.) and common purslane (Portulaca oleracea L.) at the research glasshouse of Agricultural Faculty of Ferdowsi University of Mashhad, Iran. Spraying was performed by overhead trolley sprayer (Matabi 121030 Super Agro 20 litre sprayer), 8002 flat-fan nozzle at 300 kPa and a spray volume of 200 Lha-1. The plants were treated at 21 days (at the four- to six-true leaf stage) after planting. Chlorophyll fluorescence measurements were carried out on dark-adapted leaves at the same stages of development among pots. Fluorescence emissions were measured using a portable chlorophyll fluorometer (Handy-PEA), which emits light of 650 nm wavelength with an intensity of 3000 µmol photons m−2 s−1 for 10s. Leaves were dark adapted for a minimum of 30 min prior to measurement. The fluorescence measurements were taken 4 hours after spraying (HAS) for common lambsquarters and common purslane and again at 24, 48, 72 and 168 HAS. The Kautsky curves were visually examined for the effects of time and dose by the BIOLYZER program with OJIP steps as fix points. Results Discussion: The results showed that the parameters of measured had different sensitivity to the herbicides application, So that, four hours after desmedipham + phenmedipham + ethofumesate application on weeds mentioned, maximum quantum efficiency of PSII (Fv/Fm), did not show any change whereas the relative change in J stage fluorescence (Fvj) and the area between the curve and Kautsky (Area) Fm strongly reduced during this period, but chloridazon usage was not changes on Kautsky curve and their parameters during this period due to lower solubility, and sediment deposition in the sprayer tank mix. Common purslane was more affected by desmedipham + phenmedipham + ethofumesate application because of sponge leaves and stems while common lambsquarters had lesser sensitivity to both of herbicides application due to powdery and white cover over leaves and stems. Among chlorophyll fluorescence parameters measured, Fvj was appropriate parameter and quicker to detect the herbicides effects on both of experiments plants. Conclusion: In conclusion, various fluorescence parameters can be used to describe the shape and change of Kautsky curves in different plant species. In this paper we focused on common fluorescence parameters for two tested herbicides. The parameter Fv/Fm seems to be less sensitive to detecting changes than are Fvj and area. Since chlorophyll fluorescence parameters were affected after herbicide application immediately; therefore, it could be used as a practical tool for assessing the efficacy of herbicides in the early hours after spraying herbicides in the greenhouse and field experiments

The Effect of Relative Emergence Time and Density of Common Lambsquarters (Chenopodium album L.) on Corn (Zea mays L.) Grain and Biological Yield

Abstract To study the effect of competitive potential of corn (Zea mays), in competition with common lambsquarters (Chenopodium album) an experiment was conducted in 2006, at the farm of Agricultural Faculty of Ferdowsi University. In this experiment the effect of relative emergence time of common lambsquarters on single Cross 704 corn yield was studied in different densitis of the weed. The experimental design was split plot based on randomized completed block design with three replications. The emergence time at 3 levels (emergence of the weed 14 days earlier, 7 days earlier and simultaneously with corn) was considered as main plots and density of weed at 6 levels (0, 4, 8, 12, 16 and 20 plants m-2) as sub plots. The results showed a decrease in grain and biological yield of corn, as the emergence time of corn delayed in comparison with the emergence time of weed. The maximum yield reduction of 100 and 99% was observed respectively, in the earliest emergence time of common lambsquarters compared to corn and in the highest density of weed (20 plants m-2) where the corn plants were fully shaded by the weed canopy and no ear was produced. The yield loss of corn was higher when the earlier emergence time of weed was occurred in higher weed densities. based on the results of this research it can be concluded that the decrease of competitive potential of corn with increasing the relative emergence time of common lambsquarters was led to significant yield loss of corn crop. While the increase in weed density resulted in corn yield reduction, there was no difference in yield loss in high weed densities. Keywords: Biomass, Competition, Weed interference model, Yield los