Control of weed barley species in winter wheat with sulfosulfuron at different rates and times of application

Field experiments were conducted at five locations in the major wheat production regions of Iran to evaluate the efficacy of sulfosulfuron in controlling weed barley species (including Hordeum spontaneum , Hordeum murinum , Hordeum distichon , and Hordeum vulgare ) in the 2004–2005 and 2005–2006 growing seasons. Sulfosulfuron was applied either postemergence (POST) or preplant-incorporated (PPI) at 0, 20.25, 30.75, 40.5, 51.0, 60.75 or 71.25 g ai ha⁻¹ to plots arranged in a randomized complete block design with four replications. Sulfosulfuron at the recommended rate (20.25 g ai ha⁻¹) failed to provide acceptable control of the weed barley species. However, the level of control increased with the application rate, particularly at rates >51.0 g ai ha⁻¹. Generally, PPI-applied sulfosulfuron resulted in markedly greater control levels than those of a POST application and complete control of H. murinum and H. vulgare was achieved with PPI-applied sulfosulfuron at all rates >20.25 and 30.75 g ai ha⁻¹, respectively. In most cases, the wheat yield increased with the application rate without any crop injury. The highest yield increase (186%) was obtained with a PPI application of 71.25 g ai ha⁻¹.     

Confirmed resistance to aryloxyphenoxypropionate herbicides in Phalaris minor populations in Iran

Phalaris minor (littleseed canary grass) is a major weed in wheat fields in some parts of Iran. Diclofop‐methyl, fenoxaprop‐P‐ethyl, and clodinafop‐propargyl are three acetyl coenzyme A carboxylase (ACCase)‐inhibiting herbicides that are commonly used to control this grass in wheat fields. Thirty‐four P. minor populations with suspected resistance to ACCase‐inhibiting herbicides were sampled from wheat fields in the provinces of Fars and Golestan in Iran. The dose–response assays that were conducted under controlled greenhouse conditions indicated that 14 populations were resistant to fenoxaprop‐P‐ethyl, seven populations were resistant to both fenoxaprop‐P‐ethyl and diclofop‐methyl, and three populations were resistant to fenoxaprop‐P‐ethyl, diclofop‐methyl, and clodinafop‐propargyl. These populations showed different levels of resistance to the applied herbicides, compared to the susceptible population. These results suggest that different mechanisms of resistance could be involved. The enzyme assay revealed that the existence of modified ACCase in the three most‐resistant populations (AR, MR4, and SR3) is responsible for the resistance of these populations.     

Optimizing the performance of diclofop-methyl, cycloxydim, and clodinafop-propargyl on littleseed canarygrass (Phalaris minor) and wild oat (Avena ludoviciana) control with adjuvants

Optimizing the herbicide dose by the addition of adjuvants is an acceptable way to reduce the risk of side-effects from herbicides. Therefore, to detect a suitable adjuvant for diclofop-methyl, cycloxydim, and clodinafop-propargyl against littleseed canarygrass ( Phalaris minor ) and wild oat ( Avena ludoviciana ), six dose–response experiments were conducted. The treatments consisted of diclofop-methyl at 0, 112, 225, 450, 675, and 900 g ai ha⁻¹, cycloxydim at 0, 15, 30, 60, 90, and 120 g ai ha⁻¹, and clodinafop-propargyl at 0, 8, 16, 32, 48, and 64 g ai ha⁻¹ with and without the adjuvants of Frigate, olive oil, and castor oil at 0.2% (v/v) in order to control both littleseed canarygrass and wild oat. Tested herbicides performance was enhanced by all adjuvants against littleseed canarygrass and wild oat. The addition of Frigate and the vegetable oils had the lowest and the highest effect on the performance of all of the herbicides on both littleseed canarygrass and wild oat, respectively, which confirms the solubilizing nature of the cuticular waxes by vegetable oils. A comparison between the two vegetable oils revealed that olive oil exerted a greater control of littleseed canarygrass than did the castor oil. In contrast, castor oil exerted a greater control of wild oat than did the olive oil, which can be related to differences in the leaf surface micromorphology of the weeds.     

Response of winter wheat (Triticum aestivum L.) and weeds to tank mixtures of 2,4-D plus MCPA with clodinafop propargyl

Field and greenhouse experiments were conducted in 2004 and 2005 to study weed control and the response of winter wheat to tank mixtures of 2,4-D plus MCPA with clodinafop propargyl. The field experiments were conducted at Yazd and Oroumieh, Iran, with factorial combinations of 2,4-D plus MCPA at 0, 975, and 1300 g ai ha⁻¹ and with clodinafop propargyl at 0, 64, 80, 96, and 112 g ai ha⁻¹ in four replications. The greenhouse experiments further evaluated the effect of these tank mixtures on weed control, where each herbicide mixture was considered as one treatment and the experiment was established in a randomized complete block design with four replications. In the field experiments, the herbicides were applied at wheat tillering, while in the greenhouse experiments they were applied at the beginning of the tillering stage and at the four-leaf stage of the grass and broadleaf weeds, respectively. The results indicated antagonistic effects between 2,4-D plus MCPA and clodinafop propargyl. The best tank mixture with regard to weed control efficacy was 2,4-D plus MCPA at 975 g ai ha⁻¹ with clodinafop propargyl at 96 g ai ha⁻¹. The wheat grain yield was also increased by the tank mixture of clodinafop propargyl with 2,4-D plus MCPA. Generally, to inhibit clodinafop propargyl efficacy reduction due to tank-mixing with 2,4-D plus MCPA, it is recommended that the application dose of 64 g ai ha⁻¹ should be increased to 96 g ai ha⁻¹.     

Increased foliar activity of clodinafop‐propargyl and/or tribenuron‐methyl by surfactants and their synergistic action on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis)

Surfactants can improve postemergence herbicide efficacy and reduce the amount of herbicide required to obtain weed control. The effect of surfactants on the efficacy of herbicides is complicated and depends on the interaction among the plant, surfactant, and herbicide. The effects of surfactants on the efficacy of clodinafop‐propargyl and/or tribenuron‐methyl on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis) under greenhouse conditions were investigated. In addition, the surface tension of aqueous solutions of the surfactants and surfactants + herbicides was determined. Significantly lower surface tension values were obtained with the aqueous solutions of citofrigate (Citogate plus Frigate) alone and with the herbicides used in this study. The citofrigate surfactant lead to the greatest enhancement of clodinafop‐propargyl and/or tribenuron‐methyl efficacy and the effect was species‐dependent. The efficacy of clodinafop‐propargyl and/or tribenuron‐methyl in the presence of surfactants in controlling wild oat was higher than for wild mustard. The foliar activity of the tested herbicides rose with increasing surfactant concentrations. The tank mixture of clodinafop‐propargyl and tribenuron‐methyl showed a synergistic effect in controlling wild oat and wild mustard. The synergistic effect in controlling wild mustard was greater than for wild oat.     

Influence of corn density and planting pattern on the growth of common lambsquarters (Chenopodium album L.)

Crop density and spatial arrangement affect the potential of intraspecific and interspecific competition as they increase the canopy light absorption. The effects of the corn density and planting pattern on the growth of common lambsquarters ( Chenopodium album L.) was studied in a randomized, complete block design with three replications and factorial arrangement at University College, Aburaihan, Iran, in 2003. The plant density was the recommended density and 1.5-fold the recommended density. The planting pattern treatment also was performed at two levels: one- and two-row planting. The common lambsquarters density was 0, 5, 10, and 15 plants m⁻¹ per row. The results showed that the leaf area index, biomass production, crop growth rate, and inflorescence biomass of the dry matter of common lambsquarters were decreased by increasing the corn density. But, the leaf area index, biomass production, crop growth rate, and inflorescence biomass of the dry matter of common lambsquarters under the two-row planting pattern were less than under the one-row planting pattern, although these differences were not significant.