WEED RESEARCH JOURNAL
Year:2009 | Volume:1 | Issue:2|Papers Count:8

In order to investigate the effect of maternal environment on salinity and drought tolerance of annual sowthistle at germination and emergence stage, seeds of two populations from Birjand and Ahwaz with different climatic conditions were collected and two different factorial experiments were conducted based on CRD with three replications at research laboratory of Agriculture Faculty of Birjand University. Salinity levels were 0, 10, 20, 40, 80, 160, 240 and 320 mM of NaCl and drought levels were 0, -0.1, -0.2, -0.4, -0.6, -0.8 and -1 MPa. Results showed that examined traits including germination percentage, germination rate, root length, shoot length and seedling vigour were significantly (P≤0.01) decreased at harsh salinity and drought stresses. According to the fitted logistic model, the NaCl concentration and also the drought level required for 50% reduction of germination for Ahwaz population was much greater than that of Birjand population. This experiment results showed a greater salinity and drought tolerance of Ahwaz population than Birjand population, indicating the crucial role of the maternal environment effect on annual sowthistle germination traits. Thus, this should be considered at management and control programs of this weed species.

A laboratory experiment was conducted to determine allelopathic potential of aqueous extract of canola residues on germination traits of wheat (Triticum aestivum L.), barley (Hordeum Vulgar L.) and wild radish (Raphanus raphanistrum L.) seeds, a factorial experiment based on a completely randomized design with three replications was conducted at Agricultural Faculty of Hamedan in 2006. Treatments were three kinds of water extract of canola (shoot, root and shoot + root) and five concentrations (0, 25, 50, 75 and 100 percentage) of extracts. Polyethylene glycole (PEG) was used to distinguish between the inhibitory effect of possible allelopathic substances and effects caused by the osmotic potential of the extracts. Aqueous extract of canola showed allelopathic effects on germination and growth traits of radish. The germination percentage, shoot / root ratio, root length and seedling dry weight of radish decreased with increasing concentration of canola residue. Root length and seedling dry weight of radish showed the most sensitive to canola extract. The aqueous extract of root and shoot had the maximum and minimum allelopathic effects respectively. Unlike barley aqueous extract of canola residues did not have any allelopathic effect on wheat, unlike barley. The extract of canola had no effects on germination and growth of barley by decreasing the germination percent, root length and seedling dry weight. Root length and seedling dry weight of barley were very sensitive to canola residue. Different concentrations of PEG had no significant effects on studied germination traits, therefore inhibitory effects of extracts can be attributed to an allelochemical effect.

Ceratocarpus arenarius L. is one of the problematic and noxious weeds in dryland farming of wheat, barley, lentil and peas in north of Khorasan. In order to determine the effects of temperature, light, salinity and drought stress and burial depth on seed germination and seedling emergence of this species, experiments were conducted in the Research Laboratory of Birjand Faculty of Agriculture. Ceratocarpus seeds had identical germination in either light/dark and continuous dark regimes, indicating this weed species is non-photoblastic. Seeds germinated over 85% in the range of alternating day/night temperatures (20/10, 25/15 and 30/20oC) and the maximum germinability (96%) was observed at 25/15oC. Ceratocarpus arenarius seeds maintained their germinability at high levels of salinity and drought stress, so that at NaCl concentration of 800 mM and osmotic potential of -1 MPa seed germination was 20 and 25%, respectively, indicating this species is tolerant to salinity and drought stress. Seedlings could emerge from a range of burial depth from 0 to 6cm and maximum emergence (94%) was observed from seeds planted on the soil surface covered with 3 layers of filter paper. This shows that minimum- and no-till systems would increase seedling emergence of this species through keeping crop residues on the soil surface.

A field experiment was conducted to determine the effect of various corn and bean intercropping densities on weed population in Agricultural Research Station Ferdowsi University of Mashhad. The experimental Treatments were included: corn intercropping with bean at the common density of bean plus 10%, 20% and 30% increased in bean density, bean intercropping with corn at the common density of corn plus 10%, 20% and 30% increased in corn density and control treatments (sole crops of corn and bean). This experiment was conducted in a low input production system. The results indicated that intercropping treatments lead to reduction of weed effect when compared with sole cropping. Increasing in crop plant density lead to reduction of weed biomass. The highest and the lowest weed dry weight was resulted from the sole corn treatment (29.17 g m-2) and the bean intercropping with corn at the common density of corn plus 30% treatment (4.97 g m-2), respectively. Corn and bean Intercropping had significant effects on yield. The highest and the lowest bean biological and economical yield were obtained from the sole cropping of bean with 5.3 and 1.6 ton/ha and bean intercropping with corn at the common density of bean plus 30% with 2.7 and 0.7 ton/ha, respectively. The highest corn biological and economical yield were obtained in the sole cropping of corn with 14.7 and 7.3 ton/ha, respectively. The highest (1.56) and the lowest (0.77) land equivalent ratio also was obtained from the intercropping of corn with common density of bean plus 10% treatment and from the intercropping of bean with corn at common density of corn plus 30% treatment, respectively.

An experiment was conducted at Pakdasht barley fields in 2004 & 2005 growing seasons to study the effect of chemical control on weed seed bank in rotation systems. Corn-barely rotation with and without chemical application was implemented. Method of sampling was systematic (zigzag) and the time of the sampling stages were in two dates; before sowing and after harvesting of barley. To compare the diversity between farms, Shannon-Weiner diversity index was calculated. Weed seed bank densities in chemical managed farms (CMFs) was generally lower than those without chemical control (NCMFs). At first sampling, average weed seed bank populations in CMFs, were 49 and 31 seeds kg-1 of soil, and for NCMFs were 136 and 177 seeds kg-1 soil in 2004 and 2005, respectively. The weed seed bank density in second sampling date (post harvesting of barley) for CMFs were 33 and 30.5 seeds kg-1 soil, and for NCMFs were 210 and 254 seeds kg-1 of soil in 2004 and 2005, respectively. Seed bank density decreased over sampling times (growing season) for CMFs in 2004 as compared with NCMFs. In 2005, the NCMFs variation trend of the seed bank densities for managed farms was constant between the two stages of sampling. But the trend of variation in NCMFs was similar to that of previous year. Shannon-Weiner diversity index in CMFs was higher than those of NCMFs. Herbicide application had reduced the seed production of weeds and the ultimate seed rain into the soil seed bank. Results of this study demonstrate the importance of weed control practices in reducing weed seed bank size.

A field experiment was conducted to determine the effect of wild mustard at different densities on yield and growth indices of four rapeseed cultivars at Bay-e-Cola Agricultural Research Station (Mazandaran) in 2007. Results indicated that wild mustard densities affected the total dry mater (TDM), relative growth rate (RGR) and crop growth rate (CGR) of rapeseed. TDM, RGR, CGR, pods per plant, and seeds per pod of rapeseed were significantly decreased by increasing wild mustard density. Maximum and minimum yield losses from one plant of wild mustard relative in the R-G-S 500 (29.6%) and Sari-Gol (23.7%) cultivars.

A field trial was conducted to evaluate the efficacy of two herbicides (2,4-D +MCPA and glyphosate) for weed control in wheat. This experiment was set up as randomized complete design was used with 3 replications at Ahwaz (Shavoor) research station in 2001-2002. Treatments were included: glyphosate (0.410, 0.820, 1.230 and 1.640 kg ai/ha) 2, 4-D+MCPA (1.350 kg ai/ha), weedy and Weed free. Treatments were applied about 20 days before harvesting. Among herbicide treatments, 2, 4-D+MCPA, 1.640 and 1.230 kg ai/ha of glyphosate had maximum weed control percent respectively. glyphosate in 0.410 and 0.820 kg ai/ha couldn’t manage bindweed satisfactory and Bindweed density and its weight had significant difference in comparison with glyphosate at 1.640 kg ai/ha and 2, 4-D+MCPA. Maximum regrowth rate of bindweed was observed in check (weedy) and 0.820 kg ai/ha glyphosate. Experiment treatment had same yield except check (weed free), that had maximum grain yield in first year of experiment because of weed control don’t effect on yield in harvesting stage. 2,4-D +MCPA, glyphosate at 1.640 and 1.230 kg ai/ha had maximum yield in second year. The results showed that effect of 2,4-D+MCPA was very rapid and its effect was observed after 5 days while effect of glyphosate was observed after 15 days.

From 1967, when the first herbicide was registered in Iran, to mid 2009, 98 herbicides have been registered. There are several experimental herbicides in some stage of progress toward marketability. Currently, the greatest number of herbicides are belonging to the following groups: photosynthesis inhibitors with 23 herbicides, Acetyl coenzyme A carboxylase (ACCase) inhibitors with 16 herbicides, Acetolactate Synthase (ALS) inhibitors with 14 herbicides, 14 premixed herbicides formulations, lipid inhibitors and synthetic auxins, each with 6 herbicides. The most important weeds of main crops, orchards and vegetable fields are 214 species (105 broadleaf and 22 grasses) and 87 species are perennials. Seventy percent of these weeds are C3, 15% are C4, 1% are CAM and 13% are unknown.