نشریه دانش علفهای هرز
سال سوم شماره 1 (بهار و تابستان 1386)

Distribution and stability of purple nutsedge (Cyperus rotundus) population within four fields under corn-fallow rotation were analyzed over two growing seasons in 2005 and 2006 at the Agricultural Research Station of Ferdowsi University, Mashhad, Iran. In 2005, N-fertilizer (urea) was applied at two different application methods (whole and split application). As a result of applying or not applying herbicide (a mixture of 2,4-D and MCPA) on the fields under the same N-fertilizer management, four treatments including N(whole)-herb, N(whole)- no herb, N(split)-herb and N(split)- no herb were assigned to four fields. In 2006, the field was kept under fallow. In both years, samplings were conducted at the same points (intersections of 2.5 m-2 grids) and dates (three times). Geostatistical techniques were used to examine the data. Purple nutsedge density was higher in corn fields than the fallow condition, with average densities of 51.73 and 19.61 plants m-2, respectively. In Correspondence to: E. Mohammadvand; E-mail: el_mo19@stu-mail.um.ac.ir both years, the mean density of purple nutsedge was higher in fields with whole application of N-fertilizer compared with split application. Spherical and Exponentialmodels indicated strong or moderate spatial autocorrelation. Spatial distributions were found to be heterogeneous, with high-density patches and areas at lower density. The distribution pattern of purple nutsedge densities indicated that patch-level ‘spatial aggregation’ existed. Despite fluctuation in margins, spatial stability was observed for purple nutsedge patches. This suggests that purple nutsedge would be a good candidate for site-specific application; however more practical experiments are needed to confirm this issue.

The critical period for weed control is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. In order to determine the critical period of weed control in dry bean (Phaseolus vulgaris, Khomein cultivar), a field study was conducted at Agricultural Research Station of Lorestan University on 2004. Experimental treatments were arranged in randomized complete blocks with 4 replications. The treatments consisted of two different periods of weed interference, a critical weed-free period, and a critical time of weed removal. In the first series, treatments of increasing duration of weed control were maintained weed free until 14, 28, 42, 56 and 70 days after crop emergence (DAE). The weeds were subsequently allowed to compete until final harvest (84 days). In the second series, weed interference treatments of varying duration allowed weeds to compete Correspondence to: rmirzaei57@yahoo.com with dry bean from crop emergence until 14, 28, 42, 56 and 70 days; then the plots were weeded and kept weed-free until harvest. Maximum weed-infested and weed-free periods of 14 weeks after dry bean emergence were maintained by hand weeding. Species composition, density, dry matter of weeds, and relation to reduction of dry bean seed yield were investigated. The major weed species were Amaranthus sp 41.5%, Tribulus terrestris 37.5%, Sorghum halepense 29%, Echinochloa crus-galli 25%, Convolvulus arvensis 24% and other species 21% of the total density. The highest dry matters were recorded for Amaranthus sp, Tribulus terrestris and Sorghum halepense, respectively. Experimental treatments had significant effects (P)

In order to investigate the role of intercropping of corn/soybean on the resource use efficiency and suppression of weeds, a field experiment was carried out at the Faculty of Agriculture Research Farm, University of Tehran in 2006. Treatments were arranged in a factorial experiment based on a randomized complete block design with three replications. Treatments were five different mixing ratios of corn (Zea mays) and soybean (Glycine max) consisting of 100%: 0% (P1), 75%: 25% (P2), 50%: 50% (P3), 25%: 75% (P4) and 0%: 100% (P5). The weed infestation consisted of one weed free (W1), and three levels of weed infestation of redroot pigweed (Amaranthus retroflexus) (W2), jimson weed (Datura stramonium) (W3) and a simultaneous presence of redroot pigweed and jimson weed (W4). Weed density for both species was 15 plant m-1 of crop row in weed infested treatments. The Correspondence to: M. Aghaalikhani, maghaalikhani@modares.ac.ir results showed the highest yield of corn (9627.8 kg ha-1) was obtained in the P2W1 treatment, and the lowest (3916.7 kg ha-1) was in P2W4. But the highest yield of soybean (5050.00 kg ha-1) was seen in P5W1 and the lowest (365.67 kg ha-1) in P2W4. Some yield components of corn such as the kernel row number per ear, kernel number per row, and 1000 kernel weight were highest for P4W1, but the harvest Index was highest (0.45) for P2W1 and lowest (0.20) for P4W4. Some yield components of soybean such as pod number per plant, grain number per pod and 1000 grain weight were highest in the monoculture of soybean and the weed free treatment (P5W1). This treatment had the highest soybean harvest index. It could be concluded that decreasing the corn/soybean ratio in the cropping rows will increase the corn and soybean yield components. The highest weed biomass (376.73 g m-2) was obtained in the monoculture of soybean infested with jimson weed and redroot pigweed. Therefore, it could be stated that corn/soybean intercropping significantly reduced the weed biomass comparing to both monocultures.

Crops that better tolerate weed competition or preempt resources from weeds may reduce dependence on herbicides and benefit an integrated weed management program. A field trail was conducted to determine the morphophysiological characteristics affecting tolerance and weed suppressive ability of some winter wheat cultivars in competition with Rocket. The experimental treatments consisted of eight wheat cultivars; kept under weed free and weed infested conditions in a randomized complete block design with a factorial arrangement. The results indicated that Correspondence to: deihim59@yahoo.comand deihim@sbu.ac.ir cultivars with greater harvest index (HI) or ability to prevent HI losses in competition with Rocket could balance yield losses and consequently increase their tolerance. Height increase in more competitive cultivars in competition with Rocket, was important in the competitive ability (CA) of these cultivars (as both tolerance and suppressive ability). Those cultivars with higher CA, were taller or had greater rate of stem elongation. Enhancement rate of stem elongation caused an earlier closure of canopy in more competitive cultivars, and consequently through shading on weed, suppressed the Rocket growth. In conclusion, more competitive cultivars possessed a set of characteristics that contribute to their strong competitive ability including high leaf area and vertical leaf area distribution, taller and greater rate of stem elongation, and high early vigor (viability and speed of germination).

Sunflower (Helinathus annuus) is a susceptible host to the holoparasite hemp broomrape (Orobanche ramosa) in central parts of Iran, causing yield loss due to severe infestations. A field study was conducted in 2006 to evaluate the efficacy of glyphosate for controlling the parasitic weed hemp broomrape in sunflower. Glyphosate was applied once or twice at five rates ranging from 0.075 to 0.450 kg ae ha-1. Most efficient control was obtained from once or twice application of gyphosae at 0.225 and 0.350 kg ae ha-1 at both application times. There were a significant reduction in hemp broomrape dry weight at 0.225 and 0.350 kg ae ha-1 (75 and 87.5 %), respectively compared to control. Glyphosate at 0.075 kg ae ha-1 was not sufficient enough to provide acceptable control, but duplicating the application of this rate provided good control of weed. Nearly no hemp broomrape shoot and dry weight were measured when glyphosate was applied twice at 0.450 kg ae ha-1. However, sunflower grain yield loss (63%) resulting from glyphosate toxicity at 0.450 kg ae ha-1 was observed when applied twice, compared to its application at 0.225 kg ae ha-Correspondence to: Y. Filizadeh, filizadeh@shahed.ac.ir Results showed that hemp broomrape was unable to survive after the twice application of glyphosate at 0.225 or 0.350 kg ae ha-1.

The common reed (Phragmites australis) is a perennial weed with the largest geographical distribution of any flowering plant in the world. In this study, 39 populations of common reed were collected and random amplified polymorphic DNA (RAPD) markers were used to characterize the genetic diversity among these populations. The 16 primers used in this study, amplified 149 scorable RAPD bands among which 123 were polymorphic (82%). Genetic similarity coefficients ranged from 0.44 to 0.84, with an average of 0.60. Results showed that RAPD markers are suitable for the evaluation of genetic diversity of common reed. The results support the clonal nature of P.australis with its growth and spread primarily by vegetative propagation

In order to analyze the competition of volunteer rye (Secale cereale) with wheat (Triticum aestivum), two experiments were carried out at Mashhad and Gonabad Agricultural Research Stations during the 1998-1999 growing season. In this study, wheat at 450, 460, 470, 490 and 530 plant m-2 and feral rye at of 10, 20, 40, and 80 plants m-2 in association with 450 wheat plants m-2 were considered as the main treatments. The second factor included two weed free and weedy checks. Results indicated that volunteer rye had a higher competitive ability compared to wheat. Wheat yield was significantly lower in treatments associated with rye plants compared to pure stands of wheat. However, at a density of 20 plants m-2 of rye weed, no significant differences in grain as well as biological yield were observed. There were significant differences between weed free and weedy treatments considering grain yield, biological yield and yield components.

Polypogon (Poaceae), a Mediterranean - Southwest Asian genus with about 18 species in world and 4 species in Iran is a common adventive genus of open habitats. These halophytic or glycophytic species grow in moist areas of different habitats of Iran. These species grow in Irano-Turanian and Saharo-Sindian regions in Iran. In this study, accessions of Polypogon were collected from its distribution regions in Iran. There are difficulties in recognition of some Polypogon species by traditional identification keys. Biometrical analysis was done using 46 quantitative and qualitative morphological characters from which 13 characters were of diagnostic values. Characters such as glume apex, hairs frequency and shape, spike compactness and ligule shape were main diagnostic features of this genus in Iran. An identification key based on evaluated characters by factor analysis and principle component analysis was provided and species affinities were evaluated

Morphophysiological variations of field bindweed populations in Tehran province was studied during 2006 and 2007 growing seasons using multivariate analysis methods. To determine the variations, 43 morphological and physiological characters were considered biometrically. The main characters at principal component analysis (PCA) consisted of leaf dry weight, shoot dry weight, and leaf area to identify the biotypes. But, the populations were identified based on allometric variables, particularly root weight ratio. The results suggested that field bindweed ecotypes have been formed while the species adapted to specific geographic locations. Factor analysis based on PCA revealed that twelve factors comprise almost 85% of total variations for field bindweed populations in three locations of Tehran province. Phenological and morphological variabilities among biotypes may explain the survival and adaptability of a population of this weed as a result of environmental and field management changes