The effect of seven herbicides (U-46 Combi Fluid, Cruz, MR, Basagran Bromicide, Lumax, and Gramoxone) on Xanthium strumarium plants was studied. Chlorophyll content and fluorescence, leaf temperature, and stomatal conductance were evaluated at 12 h, 36 h, 60 h, and 84 h after herbicides application. U46 Combi Fluid, Cruz, and MR did not have a significant effect on chlorophyll fluorescence induction curves as compared to the control treatment. However, Basagran, Bromicide, Lumax, and Gramoxone showed significant changes in the shape of polyphasic fluorescence transients (OJIP transients). Variations in chlorophyll content index, leaf temperature, and stomatal conductance parameters were dependent on the type of applied herbicide. Our study revealed that the specific impact of the applied herbicides on the photosynthetic efficiency of plants is related to their chemical groups and their mechanism of action.

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Dodder (Cuscuta campestris Yunck.) is one of the parasitic weeds that cause yield losses of many crops and orchards. Control of this weed is very difficult. This experiment was carried out to assay the effects of different concentrations [0 (distilled water as a control), 1.25%, 2.5%, and 5% (gram powder of plant per 100 ml of distilled water)] of lavender (Lavandula vera DC.), rosemary (Rosmarinus officinalis L.), garden sage (Salvia officinalis L.), thyme (Thymus vulgaris L.), and common balm (Melisa officinalis L.) on dodder seed germination and seedling growth. Results showed that all of these medicinal plants had significantly effect on dodder seed germination and seedling growth. So that the highest concentration of lavender, thyme, garden sage, common balm, and rosemary, respectively; dodder seed germination was reduced 58.25%, 25.25%, 25%, 23. 5%, and 11.25%, respectively. Seedling growth of dodder was more sensitive than that of germination against extract concentration of all medicinal plant. The present study shows that the inhibitory effect of lavender aqueous extract on germination and seedling growth of dodder was more than that of other medicinal plant tested in this experiment. These results showed inhibitory effects of these medicinal plants extract on dodder seed germination and seedling growth.

Alfalfa is one of the most widely grown forage crops in Iran, especially in Shabestar county. Weeds play a significant role in reducing the feeding value of alfalfa. Weed survey was done in order to determine environmental factors on weed species distribution in alfalfa fields at Shabestar, Iran (2010-2011. The family dominance index (FDI) and relative dominance (RD) were used to find dominant families and species for infestation of Shabestar's alfalfa fields. Data were analyzed by principal component analysis (PCA) and canonical correspondence analysis (CCA). A total of 130 weed species belonging to 28 families were observed. The most dominant families, based on the FDI, were Asteraceae, Poaceae, and Brassicaceae with 66.3, 61.8, and 41.1 FDI, respectively. Alopecurus myosuroides and Convolvulus arvensis were the most dominant species according to the RD index, measuring 26.4 and 21.8, respectively. PCA showed that some weed species only infested specific areas, but a few species with broader environmental tolerances were found near origin. Most variation in species distribution was explained by altitude, which was followed by soil potassium and salinity content of the soil. Our results suggest that the effect of altitude was more important than other environmental factors.

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