IRANIAN JOURNAL OF WEED SCIENCE
Year:2009 | Volume:5 | Issue:1|Papers Count:8

To evaluate the resistance of winter wild oat (Avena ludoviciana) biotypes to pinoxaden, Whole plant bioassay experiment was conducted at Department of Weed Science, Plant Protection Institute, in 2008. Twelve putative resistant and one susceptible populations that had been collected from wheat fields of Fars province were surveyed in a doseresponse experiment. All populations were exposed to a range of pinoxaden dosages including 0.25 to 16 times the recommended dose (45 g a.i. ha-1). Results indicated that herbicide resistance was occurred in major of winter wild oat populations. The resistance index based on dry weight and plant survival was estimated in the range from 2.21 to 26.89 and 1.43 to 18.48, respectively. Four of 12 populations (F2, S2, S4 and ES4) showed high resistant to pinoxaden with resistance ratio >12 fold greater than the susceptible population. But the populations of M2 and ES indicated intense sensitivity to pinoxaden.

For investigation of the effects of seedbed preparation time and plant density of sugar beet on the weed population and quality and quantity characteristics of sugar beet, an experiment was conducted as strip plot design with four replications in the field of Islamic Azad University of Karaj (2007-2008). The first factor included two types of seedbed preparation time (spring and autumn), the second factor included four plant densities of sugar beet (65, 73, 81 and 99 thousand plants per hectare). Seedbed preparation methods were considered as a randomized complete block design and plant density levels as the Latin square design. The result of analysis of variance for the traits related to weeds showed that the effect of seedbed preparation method was significant on number of weed species and weed dry weight. The results of mean comparison showed that the number of weed species and weed dry weight of spring seedbed preparation method was 2-3 times grater than autumn seedbed preparation method. Increasing plant density of sugar beet from 65 to 99 thousand plants per hectare reduced significantly the number and weed dry weight of weed species. The results of yield and quality of sugar beet showed that seedbed preparation in autumn, increased root yield (48.18 t. ha-1) by 21 percent, sugar yield (8.3 t. ha-1) by 26 percent and white sugar yield (6.7 t. ha-1) by 24 percent compared to spring time seedbed preparation. Maximum yield of sugar beet was obtained in plant density of about 100,000 plants per hectare. In conclusion, seedbed preparation in autumn and drilling sugar beet seed in the early spring with 100 thousand plants per hectare may consider as a compilation method to suppress weed populations and increase sugar beet yield.

In order to study the effect of plant density on critical period of weed control in canola (Brassica napus L.), hybrid cultivar of hyola 401, a factorial experiment was conducted using a randomized complete blocks design with three replications at Rice Research Institute of Iran (RRII) in Rasht during 2008-2009 growing season. The factors included plant density (80 and 57 plants m-2) and periods of weed management based on growth stages the crop. These periods included five levels of weed control until crop emergence, 2, 4, 8 leaf stages and emergence of flowering bud initiation and five levels of weed interference until the above mentioned growth stages. Two additional treatments including fullseason weedy and weed free checks were also prepared. The critical period of weed control was determined with the use of 5 and 10% acceptable yield loss levels by non-linear regression method and fitting logistic and gompertz equations to relative yield data. The results showed that the critical period of weed control in a density of 80 plants m-2 was between emergence to flowering bud initiation and planting to flowering (31.5-108.4 and 13.5-139.4 days after planting) and In a density of 57 plants m-2 was also between emergence to flowering and planting to flowering (25.5-115 and 4-143 days after planting) considering 10 and 5% acceptable yield loss, respectively. Therefore, the critical period started earlier and was also longer in a density of 57 plants than the density of 80 plants m-2. Weeds in field due to fall product were divided into fall and spring categories. Fall weeds in order of importance (in terms of density) were Poa trivialis, Phalaris minor, Ranunculus bulbosus and Rumex crispus. Spring weeds also were Erigeron Canadensis and Lythrum salicaria. The results also showed that plant density, control and interference of weeds and their interactions had significant effects on number and dry weight of weeds. The highest weed dry weight and number were related to 57 plants m-2 on interference treatment to 8 leaf stages.

A pot experiment was conducted to evaluate the effect of some trap crop on Egyptian broomrape damage reduction in tomato. A randomized complete block design with four replications was carried out in Agronomy Faculty, University of Tehran, Karaj, during 2008 & 2009. In the first year, seven trap crops including Egyptian clover, sesame, mungbean common Flax, garlic, cotton, and black-eyed pea were cultivated in pots and harvested at the end of the season. In the next year tomato transplants were cultivated in the same pots and after two months, pots were evaluated. Shoot and root weight of tomato, weight and number of tomato fruit, stem and tuber dry weight of broom rape, number of stems and tubers of broomrape were measured. Results showed that sesame, common flax and Black-eyed pea had the most significant decrease in broomrape dry weight separately 98.6, 75.2, and 74.4 percent and number of broomrape stems respectively 100, 83.5 and 50.9 compared to without trap crop treatment and subsequently caused increasing in tomato yield. These plants have the great potential to broomrape damage reduction and can be used in rotation in infested soils with broomrape seeds.

In order to select appropriate combined model to describe the relationship between herbicide dose–response and nitrogen fertilizer levels in predicting jimsonweed and redroot pigweed control a experiment was laid out in a factorial design based on complete randomized design (CRD) with three replicates in research greenhouses of Agriculture Campus of Tehran University, Karaj in 2009. The four levels of nitrogen (0, 90, 180 and 360 kg ha-1 urea fertilizer) and five levels of Nicosulfuron (0, 0.5, 1, 1.5 and 2 L.ha-1) were applied. Analysis of variance demonstrated the there were significant effects of fertilizer and herbicide treatment and interaction between herbicide and nitrogen on both of weed biomass. The standard dose–response curve was considered for base model. Then efficiency of this model assesses to weed biomass determination at each nitrogen level that accuracy of this model confirms. For determination of relation each of parameters of base model with fertilizer levels, possible models were considered and appropriate models as submodel were settled at base model, ultimately final combined model presented. The biomass of both weeds at noherbicide treatment (Wo) showed a different behavior with increasing nitrogen. Trend of these changes at nitrogen levels was well described by the linear and quadratic models for redroot pigweed and jimsonweed, respectively. Increasing nitrogen didn’t change herbicide dose-response of jimsonweed, because steepness of the curve (b) and the effective dose required to reduce weed biomass by 50% (ED50) parameters of this weed not showed a clear behavior with increasing nitrogen. Therefore standard dose–response curve with constant b and ED50 parameters was best describing of jimsonweed biomass as affected by both the herbicide dose and nitrogen level. But standard dose–response curve of redroot pigweed was modified by replacing the parameter b and ED50 with the exponential and linear curves, respectively. The final presented models can be used to predict weed control by an herbicide as affected by both the herbicide dose and nitrogen level.

In order to identify the density and abundance of weeds in barely fields of Azarbayjan-e-shargi Province, 80 fields in 19 towns for two years (2008-2009) were investigated. A total of 219 weed species from 36 families were observed within the barely fields. Among 219 species recorded, 107 species occurred in more than three township and 120 species occurred in more than three fields. Maximum weed densities were found in the Garaaghaj, Maragheh and Malekan with 20.82, 22.17 and 22.18 plant/m2, respectively and minimum in the Varzagan, Sarab, and Bonab with 91.77, 85.61 and 82.97 plant/ m2, respectively. The 116 species of 219 species belonging to four major families, Asteraceae, Brassicaceae, Poaceae, and Fabaceae, with 42, 30, 24, and 20 species, respectively. Prostrate knotweed (Polygonum aviculare), bindweed (Convolvulus arvensis), and threehorned straw (Gallium tricornutum) were dominant species based on a abundance index (AI). Hashtrud, Kaleybar and Jolfa with 93, 87 and 82 species, respectively, had maximum diversity in weed community and Malekan, Garaaghaj and Ajabshir with 10, 21 and 22 species, respectively had minimum diversity.

A combination of plant residues and increased crop density would play an important role in enhancing crop growth through weed suppression in organic agriculture. In order to attain the best level of wheat residue amount and sunflower density, a factorial experiment based on RCBD with three replications was conducted at research field of the Faculty of Agriculture of Birjand University (Amirabaad campus) in 2008 growing season. Treatments were 5 different rates of wheat residue including 0, 250, 1250, 3750 and 5000 kg ha-1 and 3 sunflower densities including 50000, 70000 and 90000 plants ha-1. Results showed that the maximum crop growth as well as the lowest weed growth was observed at the density of 70000 plants ha-1 and 3000 kg ha-1 of wheat residue. Increasing crop density and residue amount to the levels above these limits would have no effect, or even in some cases reduce crop growth.

In order to investigate the effect of corn/soybean intercrop on their yield and growth indices under competition with redroot pigweed (Amaranthus retroflexus L.) and jimson weed (Datura stramonium L.), a field study was carried out in Karaj during 2007 growing season. Treatments were arranged in a factorial experiment based on randomized complete blocks with three replications. Experimental factors were five different mixing ratios of corn (Zea mays L.) and soybean (Glycine max L.) including: 100: 0 (corn/soybean), 75:25, 50:50, 25:75 and 0:100 with four levels of weed infestations: weed free, infestation to redroot pigweed, infestation to jimsonweed and co-occurrence of both weeds. Weed density was 15 plants per meter of row. Results showed that corn leaf area index, dry matter accumulation and crop growth rate was maximum in 75:25 (corn: soybean) ratio. The highest land equivalent ratio (1.33) and the most amount of corn yield (10875 kg ha-1) was also observed in this ratio, but decreased as the proportion of corn was decreased in mixture. The maximum corn yield loss occurred from multiple weed competition treatments. LAI, CGR, dry matter accumulation and grain yield (5898.3 kg ha-1) were maximum for soybean pure stand but showed a decreasing trend with decreasing soybean ratio. Appearance of high LER in all intercropped plots even in weed infested treatments indicate to profitability of intercropping as a non-chemical strategy for weed management.