IRANIAN JOURNAL OF WEED SCIENCE
Year:2013 | Volume:9 | Issue:1|Papers Count:8

An audit was made for weed science in Iran by Iranian Society of Weed Science for the years 2009 and 2010. All the information was collected by filling special forms. Other information was collected by media search. All collected data was processed and analyzed according to the requirements of this report. Results indicated that the number of MSc candidates accepted for weed science in six state universities was 86 and ten Islamic Azad university branches, 443, during the two years of this survey. At the same period, 18 PhD candidates were accepted in the two state universities (Tehran and Mashhad). The number of scientific body of weed science specialists at the above mentioned universities was 18 in state and 10 in Islamic Azad university branches. In the research sector, there were 97 researchers active in weed research at the Ministry of Agriculture research units of whom 41 were members of the scientific body. A total of 356 scientific articles were published during this study period, of which 30 were ISI grade and 9 extension category. Amongst the 30 ISI articles, 21 were from state universities, 6 Islamic Azad university branches and 3 from agricultural research units. It was also shown that 62.02% of all the published articles were of basic nature and 37.92%, applied. The above data also revealed that, on the average, for every member of the scientific body of universities and research units, 2.56 articles have been published (3.81 for state universities, 1.67 for Islamic Azad university branches and 1.76 for agricultural research units). As for articles presented at Iranian and foreign conferences, a total of 620 articles were recorded. The subject of 194 were chemical, 168 non-chemical, 180 basic and 78 biological studies. During This period, 15 weed science books (12 authored, 3 translations) were published, four of which belonged to state universities, one from Islamic Azad university branches and 10 from agricultural research units. During the period of this survey, 240 theses were presented, of which 71 belonged to state universities and 169 came from Islamic Azad university branches.

Knowledge about weed seedling emergence pattern provides helpful information to improve management decision making. Emergence pattern is genetically controlled and built up in association with environmental conditions. Six Hordeum spontaneum Koch populations that collected from different climates around Iran, were sown in field in a complete randomized block design with 4 replications. Seedlings were counted using the fixed quadrates at 3- day intervals until no emergence occurred in field. Cumulative emergence against thermal time (GDD) was described with sigmoid function for each population. Parameter estimates indicated appearance of populations in field with different patterns. Kermanshah population was the first seedlings emerged receiving 67 GDD followed by Khorasan Razavi populations which emerged 2-weeks later (76.6 GDD). Tehran and Ghazvin populations showing similar pattern appeared in field at GDD of 76.6. Fars and Khozestan were the last populations emerged in field with receiving 83 and 88 GDD, respectively. There are significant correlations between emergence patterns and climate conditions form which the populations were collected.

The aim of this study was to quantify the response of germination rate to temperature and to find cardinal temperatures and thermal time required for different germination percentiles in Cyperus difformis. We compared 4 non-linear regression models [dent-like, segmented and beta (4 and 5 parameter)] to describe the germination ratetemperature relationships of C. difformis over seven constant temperatures (ranging from 15 to 45oC, with 5oC intervals). Different statistical indices [Root Mean of Squares of Error (RMSE), Akaike Information Criterion (AICc)] were used to compare models performances. The dent-like model was found to be the best model to predict germination rate (RMSE=0.0009, AICc=-380.8). The base, the lower optimum, the upper optimum and the maximum temperatures for the germination of C. difformis were estimated to be 14.73, 34.34, 38.54 and 45.01oC, respectively. The thermal time required to reach 50 and 95% germination was 43.50 and 65.01 degree-days, respectively. The cardinal temperatures depended on the model used for their estimation. Overall, the dent-like model was better suited than the other models to estimate the cardinal temperatures for the germination of C. difformis.

To survey herbicide resistant weeds in wheat fields an experiment was conducted on suspected biotypes collected from Khuzestan and Kermanshah provinces of Iran during 2010. Seeds of 30 and 50 suspected resistant wild oats biotypes collected from wheat fields of Khuzestan and Kermanshah provinces, respectively. In this study, Seeds of suspected resistance to wild oat (Avena ludoviciana) were gathered and tested in a randomized complete blocks design. Management information of fields were collected and analyzed. According to the results of Khuzestan, 66% of biotypes were resistant to Clodinafop- propargyl (Topik), 14% resistant to Iodosulfuron-methyl-sodium+ Mefenpyr-diethyl (Chevalier) € and about %11 resistant to both herbicides. Furthermore, 66% of fields used herbicides with different sites of action, but in 80% of the fields, crop rotation, the most important recommendations for reducing weed population resistant to the herbicide, was not observed. Kermanshah province had a better crop rotation in comparison with Khuzestan, and 75% of the crop rotation in this province was acceptable. On the other hand, herbicide rotation was not acceptable in this province. Thus, Clodinafop- propargyl was the main graminicide that was used in the wheat fields (77% of fields) and Tribenuron-methyl was used in 45% of the field. Generally, it seems that, in spite of the good recommendations that have provided for management of herbicide resistance in wheat fields, farmers do not fallow the recommendations. If this situation continues, herbicide resistance in several grass weed species will threaten the agronomic and economic sustainability of wheat production in some provinces of Iran.

Field experiment was conducted to study the effect of nitrogen and plant density on weed population in corn under stale seedbed planting system. This study was done in the farm of Agriculture College of Tehran University in 2010.The experiment was done in complete block design with three replications. Main plot consisted of stale seedbed and conventional seedbed preparation. Subplots consisted of four levels of nitrogen fertilizer (0, 270, 325 and 380 kg ha-1) × 3 corn densities (7, 8 and 9 plants m-2). Results showed conventional seedbed had the highest biomass of weeds at 7 plants m-2 and 325 kg N ha-1. At this treatment, stale seedbed could decrease the weed biomass by more than 96.6%. In general, stale seedbed resulted in higher values of corn growth characteristics i.e. plant biomass, height, leaf area index. Using stale seedbed, the treatment of 380 N kg ha-1+9 corn plants m-2 had the highest corn biomass and grain yield. In general, stale seedbed system in corn production can be as a useful tool to better manage the weeds, improve corn growth.

In order to determine the effect of weeds on yield and yield components of common bean (Phaseolus vulgaris L.), this research was carried out as split plot in randomized complete block, with four replications, in Khomein Bean Research Station during 1999 and 2000. There were two plots including naturally contaminated with weeds, and complete weed control. There were also eight subplots containing the following ban cultivars/lines: Dehghan, Daneshkadeh, Naz, Goli, Talash, Mahali Khomein, Sadri and Coc16 bean. Mean comparisons of traits showed that presence of weeds caused loss of 45% in yield, 39% in number of seeds for plant, 5.1% number of seeds per pod, 36% number of pods in studied cultivars/lines. Goli and Talash with the highest ability of weed competition were superior among studied cultivars. The coefficients of correlation indicated negative and significant correlation of weed dry weight with yield.

Consecutive usages of acetyl Coenzyme A carboxylase (ACCase) inhibiting herbicides to control troublesome grass weeds of wheat in Iran, has resulted in resistance of 5 grass weeds to ACCase inhibitors. Recently some resistant Avena spp. biotypes have been detected in wheat fields of Iran which have developed resistance to clodinafop propargyl, setoxydim and pinoxaden herbicides with resistance factor between 1.31 to more than 50.63. This experiment was conducted to use CAPS and dCAPS method to detect mutation probably occurred in 1781, 2041, 2078 and 2088 positions of encoding gene of ACCase enzyme and resulted in resistance of resistant wild oat biotypes to ACCase inhibiting herbicides. Results showed that the cause of resistance in 50% of the biotypes (including M4, S2, S3, S4 and ES1) was mutation at the position 1781, 10% (including M2 biotype) at the position 2041 and 10% (including M4) at the position 1781 and 2078. Generally 70% of biotypes showed mutation at least in1781, 2041 and 2078 positions. The cystein-2088-argenin substitutions were not identified as a mutation endowing resistance in any of the biotypes. In other biotypes (M1, M3, S1 and F3) mutation may have occurred in other positions of gene encoding ACCase, or the resistance in these biotypes is a non-target based mechanism.

To study the effect of mesosulfuron+iodosulfuron and clodinafop and also their mixtures with Citowett and Frigate surfactants, three greenhouse experiments were conducted on wild oat (Avena ludoviciana L.) as dose-response arrangements in completely randomized design with four replications for each treatment. Treatments included mesosulfuron+iodosulfuron alone at doses of 0, 2.4, 6, 12, 18 and 24 g ai ha-1 , clodinafop alone at doses of 0, 6.4, 16, 32, 48 and 64 g ai ha-1 and six mixture ratios of doses of the two herbicides including 100: 0%, 75: 25%, 50: 50%, 25: 75%, 10: 90% and 0: 100% with and without the surfactants of Citowett and Frigate at 0.2% (v/v). Herbicide performance was enhanced by all surfactants against wild oat. Pure mixture of herbicides with each other (without surfactants) followed CA model and showed additive effects. Mixtures with Citowett or Frigate surfactants followed Hewlett model and showed synergism on wild oat. Pure mixtures of two the herbicides showed lowest effects on wild oat compared to their mixtures with Citowett, Frigate surfactants. Mesosulfuron+iodosulfuron and clodinafop mixed with Citowett surfactant showed highest effect and Frigate surfactant showed lowest effect on wild oat.