WEED RESEARCH JOURNAL
Year:2010 | Volume:2 | Issue:1|Papers Count:8

A study was done to map weeds in irrigated wheat fields from 2001 to 2006 in Sistan and Balochistan province. In this study, 44 sample wheat fields were selected and weed species were counted in each sampling point and population indices were calculated. In each fields longitude, latitude and altitude were recorded using GPS. These data were used for producing weed map using GIS. Results showed that annual yellow sweetclover (Melilotus indicus (L.) All.), common mallow (Malva neglecta Wallr.) and prostrate knotweed (Polygonum aviculare L.) were dominant broadleaf species in irrigated wheat fields of Sistan and Balochistan province. Dominant grass weed species were japanesse brome (Bromus japonicus Thunb.ex murr), winter wild oat (Avena ludoviciana L./Dur.) and Canarygrass (Phalaris minor Retz.). Hoary cress (Cardaria draba (L.) Desv.), field bindweed (Convolvulus arvensis L.), camel’s thorns (Alhagi pseudalhagi (M.Bieb.) Desv.) and Salsola spp. were the most important disturbing plants prior to harvesting in irrigated wheat fields of Sistan and Balochestan province.

A field study was conducted in Fars at Agricultural Experimental Station of Firooz Abad Islamic Azad University in 2006 to evaluate wild mustard densities on wheat yield and yield component. Increasing wild mustard density decreased grain yield, wheat dry matter, spike per plant and seed per spike. Wild mustard had no effect on wheat height and wheat seed weight per 1000 seed. Reduced grain yield ranged from 3.1 to 29.9% at 1 to 16 wild mustard per m2, respectively. At 16 plant per m2 wild mustard reduced wheat spike per m2 by 16.2% and seed number per spike per m2 by 19.6%, when compared to weed free check. Results also showed that increase in wild mustard dry weight, due to increase in mustard density, had negative effect on wheat dry weight. Wild mustard must be controlled either before or shortly after wheat emergence if detrimental effects on wheat are to be minimized.

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.

Field studies were conducted in 2005 to determine the effectiveness of different combinations of selective herbicides for control of broadleaf weeds in sugar beet fields in Tehran (Karaj), Khorasan Razavi (Mashhad) and Western Azarbayejan (Miandoab) provinces. Weed biomass and frequency and visual evaluation of weed injury and Sugar beet yield were those traits evaluated in this experiment. Weed biomass and frequency measurements in each province indicated that (phenmedipham + desmedipham + ethofumesate) + triflusulfuron methyl was the best composition. triflusulfuron methyl + desmedipham also was another composition that produced a good result. These treatments had no good effect on bindweed. The least herbicidal effect came from chloridazon + triflusulfuron methyl and chloridazon + (phenmedipham + desmedipham + ethofumesate) which had little effect on weed biomass and frequency.

In order to study on primary growth of shoot and root in wild oat (Avena fatua L.) and wheat (Triticum aestivum L.) and assessment of their competition ability in different levels of nitrogen during vegetative stage of growth, a factorial greenhouse experiment conducted based on completely randomized block design with three replications in research glasshouse of faculty of agriculture, at Ferdowsi University of Mashhad in 2008. The first factor consisted of five different levels of nitrogen (1, 4, 8, 12 and 16 mM), the second factor was five different densities (0, 2, 4, 6 and 8 plants per pot) of wild oat and the third factor was competition condition (no-competition and competition with wheat (density of 8 plants per pot)). The experiment was finished at the end of vegetative growth stage of wheat. Results demonstrated that the effects of competition, wild oat density, nitrogen level and their binary interactions on shoot dry weight (SDW) of wild oat were significant. Increasing of nitrogen increased the SDW of wild oat in both competition and no-competition conditions. The competition of wheat could also decrease this characteristic in all nitrogen levels. The interactions of experimental factors also have significant effect on SWD of wheat as well as root dry weigh (RDW) of wild oat. Nitrogen has no significant effect on SWD of wheat in high levels of weed densities. Completion between wild oat and wheat decreased shoot/root dry weight just in wild oat and had no significant in wheat. Result totally showed that increase of nitrogen at low and high densities of wild oat, increased the dominance of wheat and wild oat, respectively.

The allelochemicals or secondary plant metabolites when are released to environment, influence the germination and seedling growth of neighbors' weeds. The aim of this study was to investigate the effect of the extract of wormwood (Artemisia annua) on the number and mass of weed seedlings and their seed germination under laboratory conditions. The Wormwood extracts were considered with different concentrations (1.25 to 20%) on the germination and seedlings growth of Zea maize, Johnsongrass (Sorghum halepense), common lambsquarter (Chenopodium album) and redroot pigweed (Amaranthus retroflexus) for 5 days. Results showed that with increasing concentration of wormwood extracts, their effects on reducing seed germination and seedling growth of the above mentioned plants was more severe. Comparison of extract effects with polyethylene glycol, revealed that reduction of Johnsongrass and common lambsquarter seed germination were attributed to the osmotic pressure of the extract, where as, inhibition of seed germination of redroot pigweed and corn was due to allelochemicals. Results showed the wormwood extract was more related to the allelopathic effect.

An experiment was conducted to determine the proper time and Atrazine dose for control of weeds in grain corn. The experiment was conducted at the University of Shiraz Agricultural Experimental Station. Experiment was in a randomized complete block design with factorial arrangement of treatments. The treatments were application time (pre-planting, 10, 20, 30 and 40 days after corn emergence) and herbicide dose (0, 0.7, 1, 1.4 and 2.1 Kga.i./ha). The carry over effects of Atrazine residues on wheat emergence were also evaluated. The experiment results showed that only corn grain number was affected by the time of application. Herbicide dose had significant effect on grain weight. Both application time and herbicide doses significantly affected dry weight of weeds. Later use of herbicide had no effect on dry weight of weeds. Due to good control of weeds by herbicide at 2.1 kg/ha, the grain yield increased significantly when compared with weedy check. Results also indicated that rate of herbicide had more effect on wheat germination percentage compared with application time. Minimum and maximum germination percentage were at 2.1 Kg/ha and control treatments respectively.

Herbicides are one of the crucial options in weed management in most agricultural production systems of world. The introduction of the new herbicide families has had many benefits including very low application rates and low mammalian toxicity. As these herbicides can also be absorbed through the foliage or roots and have high mobility in plants, leading to broad-spectrum control of weeds and having soil residual persistence that gives some control of emerging weeds after application. That is why the use of these herbicide products was rapidly accepted by agricultural producers for crop production. Although, this aspect of the new herbicides is useful for control of emerging weed during the growth season, but the herbicides residues can persist to the next season (s) and damage subsequent crops. A wide range of interrelated factors impact the fate of herbicides in soil. Understanding these factors and processes can make possible the best weed control as well as reducing the potential for injury to non-target crops. Pertinent environmental conditions consist of the chemical, physical and biological characteristics of the soil to which the pesticides are used and climatic features such as rainfall, wind, temperature and light regime. These factors particularly moisture and temperature are two key factors that determine the extent of sorption and degradation of herbicides in the soil matrix. Various mechanisms including phtodegradation, volatilization, leaching, sorption and degradation are determinant processes of herbicide behavior in the environment. The present paper is an overview of the most important processes namely sorption and degradation of herbicides in soil, the environmental factors and herbicides nature which affect the behavior of these chemical in the soil.