مجله پژوهش علف های هرز
سال ششم شماره 2 (پاییز و زمستان 1393)

The contamination of water and soil resources by pesticides is an important environmental problem of the world. There are numerous variety of nanomaterials used for environmental detoxification, including nanometals, nanooxides, nanoclays and dendrimers. Numerous studies have pointed to the degradation of pesticides by using nano-particles (zero- valent iron, and nano-TiO2 nanoparticles,). Today the use of TiO for photocatalytic degradation of pesticides is taken into consideration, since it operates in ambient temperature and pressure with low energy photons, requires no chemical reagents except oxygen in the ambient air and no expensive catalysts. The degradation of pesticides on Titanium dioxide (TiO) initiated by attraction of peroxide or hydroxyl radical and electron transfer. Due to the low cost and easy production, zero- valent iron (ZVI) is an industrially feasible remediation methodology. There is evidence to suggest possible risks. Most nanoparticles are not biodegradable and expected to accumulate in organisms and especially at higher levels in the food chain. Materials in nanoscale show unusual physical, chemical, and biological properties which may be different from those in bulk materials. Therefore the nanotechnology should be promoted in a responsible and safe manner.

The influence of water quality on glyphosate and nicosulfuron performance on barnyard-grass and velvetleaf was examined in a greenhouse study as a factorial arrangement of treatments based on a completely randomized design with 6 replications at Ferdowsi University during 2008-9. Factors included were: pH at 8 levels (3, 4, 5, 6, 7, 8, 9, and 10) obtained by using buffer solutions (+3 control pots for each pH level), CaCO3 at 6 levels (0, 100, 200, 300, 400, 500, and 600 ppm (w/v)) in combination with 0 or 3 kg/ha (NH4)2SO4 (AMS), and NaHCO3 at 6 levels (0, 100, 200, 300, 400, 500, and 600 ppm (w/v)) in combination with 0 or 0.5 L/ha NH4NO3 (AMN). The herbicide solutions were applied at the 3-4 leaf stage of the weeds at the ED50 doses estimated in a dose-response preliminary test (158 g ai/ha). The results showed that glyphosate at pH of 6 and 7 had the highest effect on barnyard-grass, similarly, the best control of velvetleaf was obtained by glyphosate at a pH of 6 that there was no significant difference between pH 7. The antagonistic effects of CaCO3 (hardness factor) and NaHCO3 (alkalinity factor) on glyphosate spray tank reduced significantly its efficiency. However, adding AMS and AMN to the spray tank decreased the adverse effects of water hardness and alkalinity, respectively, therefore improved the glyphosate performance on barnyardgrass and velvetleaf control. However, the effect of addition of AMS and AMN to the soluble herbicide for control of velvetleaf was evident over the barnyardgrass. In conclusion, the results of these experiments have highlighted the importance of water quality on glyphosate performance.

In order to identify and determine the plant density, species diversity and abundance of weeds in wheat fields of Aibak Abad region in Arak city of Iran, 50 farms in 2013 was investigated in a field study. Fields based on their area in the ranges of Less than 1 hectare, 1 to 2 hectares, 2 to 4 hectares, 4 to 8 hectares, 8 to 16 hectares were identified. According to the area of farms, randomize sampling based on w pattern was performed using 0.5 on 1 square meter quaderates. 64 weed species from 23 plant families were identified. Poaceae and Brassicaceae families with 17 percent of relative importance were the most important families. according tothe results the dominant weeds in wheat fields of Aibak Abad Based on importance were Corn flower (Centaurea depressa), Tansy mustard (Descurainia Sophia) Binweed (Convolvulus arvensis L.) Foxtail grass (Alopecurus myosuroides), Cone catchfly (Silen conidia), Cow cockle (Vaccaria pyramidata), Plumeless Thistle (Carduus pycnocephalus) and (Cardaria draba). The results showed that by increasing the area of fields, the weed plant density, weed species diversity such as Shannon-Wiener diversity index and Simpson index decreased. Analaising of questionnaires filled in by farmers showed that fieldes management approaches especially herbicide application are known as the main reason of changes in the weed species composition of irrigated wheat field of Aibak Abad.

In present study germination behavior of two populations of Cynanchum acutum L. investigated in different constant temperature, temperature fluctuations, periods of darkness / lighting and high temperature. The maximum seed germination in constant temperature was observed at 25 C in Karaj population (85.5%) and at 30 C in Kerman population (92%). while in temperature fluctuations Maximum seed germination was observed at 20/30 C in Karaj population (88%) and at 25/35 C in Kerman population (90%). Seeds of two populations were able to germinate at a wide range of temperatures. Different periods of dark / light showed no significant effect on seed germination of two populations. High temperatures a above 100 ° C caused a significant reduction in germination but Kerman population resistance was more than Karaj population in high temperatures.

To evaluate the Allelopathic effect of residue extracts of C. pubescens and C. caeruleum on A. gangetica and P. polystachion, two greenhouse and laboratory experiment were carried out at Putra University, Malaysia, in 2012. In laboratory experiment, the litter leachates of C. pubescens sicnificantly reduced seed germination (%) of both weeds, but C. caeruleum had no significant effect on seed germination of both weeds. However, both cover crops increased seed germination time – length of both weeds. Residue extracts of both cover crops reduced hypocotyl length of A. gangetica and inhibitory effect of C. caeruleum was higher than C. pubescens. However, in pot culture, the increased concentration of both cover crop extracts incorporated with soil did not affect root and shoot length, dry weight and chlorophyll content of both weed seedlings. The results of residue decomposition of these two cover crops in soil showed that phenolic compounds are not persistent in soil. The results of this experiment also showed that the Allelopathic effect of both cover crops on seed germination and seedling growth depended on weed species, and residues of both cover crops in mixture with soil did not affect the seedling growth of both weed species

Weed survey of irrigated wheat fields is the most important practice in weed management. Based on cultivation area in 7 counties of Hamedan province during six years (2000-2005), 52 sample wheat fields were selected and weed species were counted in each sampling point and population indices were calculated. In each field longitude, latitude and altitude were recorded using global positioning system (GPS). These data were used for producing weed maps using geographic information system (GIS). Results shoed that flixweed (Descurania Sophia [L.] Webb.), cornflower (Centaurea depressa M.B.) and bedstraw (Galium tricornatum Dandy) were dorminate broadleaf species in irrigated wheat fileds of Hamedan province. Dominant grasses weed species were feral rye (Secale cereale L.) and winter wild oat (Avena ludovicana Durieu.). Field bindweed (Convolvulus arvensis L.), hoary cress (Cardaria draba [L.] Desv.) and Russian knapweed (Acroptilon repens [L.] DC.) were the most important disturbing plants prior to harvesting in irrigated wheat fileds of Hamedan province.