مجله پژوهش علف های هرز
سال پنجم شماره 2 (پاییز و زمستان 1392)

In order to evaluate the spatial dynamic of weeds during growing session an experiment was conducted at Astane Ghodse Razavi experimental field. One hectare size with canola-fallow-wheat rotation was selected. Sampling was carried out by discrete systematic method in which the samples were taken from plots of 7m×7m, using 0.5m×0.5m quadrates in three stages, pre chemical control, post chemical control and pre harvesting, and species and their densities were determined. Fifteen species were observed from 196 sampling points. Total weed density in the field during the first, second and third sampling stages were 44.42, 12.16 and 3.93 plant per square meter respectively. It seems that this downward trend was as a result of control operations efficiency. Goldbachia laevigata and Chorispora tenella were most important weeds in the filed during first sampling stage. While Fumaria vaillantii and Polygonum aviculare became important at during the second stage of sampling. Also P. aviculare was the most important weed in the filed during the third sampling stage and the importance of F. vaillantii was decreased. To describe the dynamics of weeds, the geostatistic method was used and variogram functions of weeds in each three sampling stages were calculated which had spherical and exponential models. Maximum and minimum of nugget effect were 0.13 and 0.45 respectively. The ranges were also between 2.8 and 196.6m. The spatial distribution maps of weeds were drawn applying variogram parameter in Kriging interpolation that showed patchy and plow directed distribution. The results showed that presence of canola in crop rotation and corresponding control operations was effective on type and spatial distribution of weeds of studied species. In fact crop rotation with the effects on weed communities can be as an option in integrated weed management effect on weeds.

A field experiment was conducted to evaluating the performance of some post-emergence herbicides and different row spacing for weed control in direct-seeded rice at the Research Farm, Gorgan University of Agricultural Science and Natural Resources, in 2011. Treatments consisted of three crop spacing between the rows (15, 25, and 35 cm), and six chemical weed control (pendimethalin at 660 g a.i. ha-1, bentazon at 1200 g a.i. ha-1, propanil + cinosulfuron at 2160+20 g a.i. ha-1, oxadiargyl at 900 g a.i. ha-1, clodinafop propargyl + "bromoxynil + MCPA" + bentazon at 40+200+1200 g a.i. ha-1 and sethoxydim + "bromoxynil + MCPA" + bentazon at 250+200+1200 g a.i. ha-1). Weed-free treatment also was included in the experiment. The plots were divided into two sections, treatments were applied in a section and the other part of each plot was considered as the control of treated section. The pendimethalin was sprayed 7 days after sowing (DAS) and other experimental herbicide treatments were applied at 35 DAS. The dominant competitiveness weed species were Xanthium strumarium (L.), Sorghum halepense (L.) Pers., Abutilon theophrasti Medik., Amaranthus retroflexus (L.) and Echinochloa colona (L.). Effect of reduced row spacing on dry matters of weed was significant at 77 and 89 DAS. Dry matters of weeds with all the chemical weed control treatments at all stages were lower than those of their weedy checks. However, none of the herbicide treatments were as effective as the weed-free treatment in reducing the dry matter of weeds. The lowest reduction in total weed dry weight was recorded with oxadiargyl herbicide. Among the herbicides evaluated, sethoxydim + "bromoxynil + MCPA" + bentazon, propanil + cinosulfuron and clodinafop propargyl + "bromoxynil + MCPA" + bentazon perfomed well as they effectively controlled weeds comparable to the weedy checks.

In order to evaluate competitive relationships between wild mustard (Sinapis arvensis L.) and canola (Brassica napus cv. Okapi), a replacement series interference experiment was conducted in greenhouse of Agricultural Faculty of Bu-Ali Sina University, in 2010. Experiment factors included 4 levels of nitrogen (0.75, 1, 1.25 and 1.5 g.pot-1) and 5 relative density series of canola and wild mustard (1:0, 0.75:0.25, 0.5:0.5, 0.25:0.75 and 0:1). Plant density of each species was 4 plants per pot at pure culture. At all nitrogen levels, intra-specific competitive coefficients of canola based on biological and grain yield were less than inter-specific competitive coefficients, but in wild mustard the intra-specific competition coefficients were higher than inter-specific competition coefficients. Relative competitive ability (RCA) of canola based on both mentioned traits were less than wild mustard, at all nitrogen levels. Increasing nitrogen rate to 1.25 g.pot-1 led to increment of RCA of canola. Increasing canola density increased its seed number per pod and pod number per plant, but by increasing wild mustard density per pot, contrary results for mentioned traits in weed were obtained. Nich differentiation indices (NDI) of biological and grain yield estimated less than 1 at 4 levels of nitrogen. NDI of biological yield was more than that of grain yield. Maximum NDI of both mentioned traits, obtained in 1 and 1.25 g nitrogen per pot, respectively. Generally, the results of experiment indicated that the rate of 1g pure N per pot (equivalent to 200 kg ha-1) was appropriate fertilizer treatment to increase competitive ability of canola in interference with wild mustard.

In order to investigate integrated velvetleaf (Abutilon theophrasti L.) and redroot pigweed (Amaranthus retroflexus L.) control methods under different tillage condition on soybean (Glycine max L.) yield and yield components, an experiment was carried out in a split plot with randomized complete block design (as a base design), with four replications in Ali Abad Katool district. Main plot consisted of three levels: 1) tillage with moldboard plow+disk, 2) tillage with chisel plow +disk, 3) tillage with just disk. Weed control methods applied in sub-plots included: 1) alacolor 2) metribuzin 3) bentazon 4) alacolor+cultivator 5) metribuzin+cultivator 6) bentazon+cultivator 7) cultivator 8) control (without weed control) 9) Whole weed was controlled. Variation analyses results showed that tillage treatments did not have a significant effect on density and mass of weed dry material on Amaranthus retroflexus. However this treatment has significant effects on density of Abutilon theophrasti at P≤0.01. Also no significant effect on its dry weight. Tillage with moldboard plow cause significant decrease of Abutilon theophrasti. Tillage treatment interactions on herbicides was significant on weeds density at P<0.05. Metribuzin + cultivator, bentazon + cultivator and bentazon has complete effect on compression and mass of weed dry material of Amaranthus retroflxus and Abutilon theophrasti and other weeds. Alacolor + cultivator has more control on weeds of Amaranthus retroflexus and Abutilon theophrasti in tillage with moldboard plow+disk than other tillage treatments. Effects of herbicides treatment on yield was significant P≤0.01. Bentazon + cultivator had the most impact on soybean yield (4531 kg/ha) and check treatment (weedy) had minimum soybean yield (2493 kg/ha).

Wild poinsettia (Euphorbia heterophylla L.) is a summer annual herb, belonging to the Euphorbiaceae family that has recently introduced in Iran and became a troublesome weed in soybean field in Golestan province. Experiments were conducted under laboratory and greenhouse conditions to evaluate the effects of various environmental factors (temperature, light, salinity and drought stress, pH) and planting depth on its germination. The results indicated that seeds germinated at constant temperature range of 15-45 C both in 14 h photoperiod and in darkness. However, germination was greater in the light/dark regime than in darkness, as maximum germination percentage (83%) and germination rate (11.34 seed day-1) was observed at 35 C with the 14 h photoperiod. At alternating day/night temperatures, the highest germination percentage (95%) and germination rate (12.99 seed day-1) occurred at 40/30 C. Germination was reduced with increasing draught stress and no germination was observed at -1.0 MPa. Wild poinsettia seeds germinated >80% at salt concentrations of 0-40 mM. Germination declined with increasing salinity stress. Germination was 13% at salt concentrations of 160 mM. Germination was not affected by pH levels. Maximum emergence was (88-95%) when seeds were sown at 0.2-3 cm depth in soil, with no emergence occurring at a planting depth of 6 cm. It is concluded that several environmental factors affecting the germination of wild poinsettia, and this information could help to predict the spread of wild poinsettia in new areas.

This study was conducted during 2010-11 in Karaj and to evaluate the efficacy of wheat selective herbicides for weed control in triticale. Herbicide treatments consisted of sulfosulfuron, mesosulfuron+iodosulfuron (Atlantis), metsulfuron+sulfosulfuron, isoproton+diflufenican, mesosolfuron+ iodosolfuron (Shovalieh), clodinafop-propargil, pinoxaden, diclofop methyl), pinoxaden + clodinafop-propargil, fenoxaprop-p-ethyl, tralkoxidim, difenzoquat) and flamprop-m-isopropyl. The results indicated that mesosolfuron + iodosolfuron (Atlantis) and difenzoquat significantly reduced plant number of cheat grass (Bromus tectorum), but these treat ments were not significantly different from mesosolfuron+iodosolfuron (Atlantis), isoproton+diflufenican or metsulfuron+solfosulfuron. All treatments, except flamprop-m-isopropyl, fenoxaprop-p-ethyl and clodinafop-propargil, compared with weedy chech, significantly reduced the dry weight of cheat grass. The lowest plant number of false barley (Hordeum murinum) was evaluated in treatment mesosolfuron + iodosolfuron (Atlantis), but this treatment had no significant difference from metsulfuron+sulfosulfuron or isoproton+diflufenican. All treatment, except mesosolfuron+ iodosolfuron (Shovalieh), pinoxaden, fenoxaprop-p-ethyl and difenzoquat, significantly reduced the dry weight of false barley. The number and dry weight of winter wild oat (Avena ludoviciana) in treatments sulfosulfuron and flamprop-m-isopropyl were not significantly different from weedy check, but other herbicides significantly controlled this weed. Among herbicides, pinoxaden and pinoxaden + clodinafop-propargil caused phytotoxicity on triticale, and metsulfuron+sulfosulfuron reduced its plant hight; however, these herbicides had no significant effect on crop yield. All treatment, except sulfosulfuron, significantly increased crop biological yield. Application of mesosolfuron+iodosolfuron (Atlantis) and pinoxaden significantly increased triticale grain yield, but they were not significantly different from other herbicides.

In four separate experiments, competition of different densities of feral rye (Secale cereale) and wild mustard (Sinapis arvensis) with wheat (Sayson cv.), also interference of Canada thistle (Cirsium arvens) and wild mustard with canola (Okapi cv.) were evaluated in 2008-2009 growing season, in Bu-Ali Sina University of Hamedan. Rectangular hyperbolic model, yield reduction of both crops than weed density and dry weight described properly. Increased dry weight of each three weed species than density per unit area was linearly. In interference with wheat, initial slope of yield loss (I) and economic threshold (ET) of wild mustard competition than feral rye were more and less, respectively. Inhibiting effect of Cirsium arvens on canola was more than wild mustard and had less economic threshold. Increasing dry weight of wild mustard per unit area instead of per plant, in competition with canola was less than wheat. Also ET of this weed in wheat was obtained more than canola. Except for experiment of Cirsium arvens interference with canola, in other cases when weed dry weight as criterion of yield loss was used, higher coefficient of determination (R2) and less residual mean square (RMS) than weed density was obtained. These results showed that weed dry weight, in comparison with density, was often better indicator of competitive ability and negative effects of weeds on crops. Also wild mustard interference with wheat was more competitive than feral rye. But its interference with canola showed less competitive ability as compared with broad leaf weed of Cirsium arvens.

Laboratory and greenhouse experiments were conducted to determine the phytotoxicity of Russian knapweed (Acroptilon repens L.) aqueous extract and residue separately and in combination with trifluralin on germination and other characteristics of redroot pigweed (Amaranthus retroflexus L.) and common lambsquarter (chenopodium album L.). Laboratory results showed that shoot aqueous extract was more effective on seed germination and other characteristics of redroot pigweed than root extract. However, germination percentage, germination rate, and shoot length of lambsquater were significantly affected by shoot extract as compared with root extract; in other characteristics, there were no significant difference between two extracts. Interaction effect of both shoot and root extracts with trifluralin caused more reduction in seed germination and other characteristics of two weeds than either of two extracts alone. Greenhouse results showed that, in general, residues were more effective than aqueous extracts, and shoot residues caused more reduction in seed germination and root length of pigweed significantly.