The reduction of herbicide applications is a main research priority in recent years. In order to study the effect of individual post-emergence application of sugar beet broad-leaf herbicides at four to six true-leaf stage of weeds, experiments were conducted during 2013. Treatments included untreated control and several rates of desmedipham + phenmedipham + ethofumesate, chloridazon and clopyralid on Portulaca oleracea, Solanum nigrum, Amaranthus retroflexus and Chenopodium album. A completely randomized layout with three replications was used for each herbicide. Three weeks after spraying (WAS), plants were harvested and measured their dry weight. These herbicides were more effective to control Portulaca oleracea than other weeds, thereupon minimum dose required for a satisfactory efficacy of 90% reduction of Portulaca oleracea aboveground dry matter (ED90) were 299.22, 1138.31 and 129.44 g a.i ha-1 of desmedipham + phenmedipham + ethofumesate, chloridazon and clopyralid, respectively. Solanum nigrum was more affected by clopyralid application (132.40 g a.i ha-1), and did not make significant difference in Portulaca oleracea. Chloridazon had lower effect for control of Chenopodium album due to existence of powdery covering on abaxial side of the leaves. Biomass ED50 or ED90, based on log-logistic dose–response curves, for Chenopodium album was considerably higher than other species. These results showed that tank mixtures with other herbicides may be required for satisfactory weed control and reduction in applied herbicides doses.
Chlorophyll fluorescence analysis is a simple and rapid method for detecting herbicide effects after a short time following their application in photosynthetic apparatus in plants. Chlorophyll fluorescence measurements were carried out against two broad of weeds to describe how the Kautsky curve and its parameters were affected by herbicides. Desmedipham + phenmedipham + ethofumesate changed the chlorophyll fluorescence induction curve at all time intervals except four hours after spring (HAS) in Amaranthus retroflexus L. and at all doses of Portulaca oleracea L. 4 HAS. In contrast, chlorophyll fluorescence inhibition was evident by chloridazon at doses of 650 and 325 g a.i. ha -1 in P. oleracea and A. retroflexus respectively, for all time intervals. Furthermore, chlorophyll fluorescence decays only occurred by clopyralid in A. retroflexus at the highest dose. A biomass effective dose (ED 50 and/or ED 90 ) based on log-logistic dose-response curves for A. retroflexus were considerably higher than that of P. oleracea. The maximum quantum efficiency (F V /F m ) was stable, whereas the relative changes at the J step (F vj ) and area (the area between the Kautsky curve and the maximum fluorescence (F m )) was more sensitive to all three herbicides. There was a relatively good correlation between fluorescence parameters taken 24 hours after the spraying and the dry matter taken three weeks later, for both species under study.
Scotch thistle is a weed species on farmlands and pastures in parts of the west and northwest of Iran. Cypselas can remain in the soil seedbank over a prolonged period due to varying degrees of dormancy. This study examined different methods for breaking cypselas dormancy in two local populations of scotch thistle at the research laboratory, agricultural faculty of Azarbaijan Shahid Madani University in 2020. In these experiments, the effect of sulfuric acid, wet and dry pre-chilling, potassium nitrate, and gibberellic acid were evaluated on the breaking of dormancy. All the experiments were conducted as a completely randomized design with four replications and two runs. The response of two local populations of scotch thistle were similar, and no significant difference was observed. The experiment treatments significantly increased cypselas germination compared with the control. Maximum germination percent were observed by soaking in sulfuric acid 98% for 10 min (60.60%), KNO3 for 96 h (69.36%), GA3 for 48 h (88.43%), and wet pre-chilling for 72 h (34.61%). Although pre-chilling increased germination, it was suggested that germination could be more than recorded values if the duration of wet pre-chilling increased. The best cypselas germination rate, mean germination time, T50, radicle, and plumule length were observed soaking in GA3 for 48 h and KNO3 for 96 h. It seems that water-soluble inhibitors in the embryo and probably cypselas coat caused to seed dormancy in this weed species. These findings could help develop effective management strategies associated with the dormancy of cypselas for this species.
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