نشریه دانش علفهای هرز
سال هفتم شماره 1 (بهار و تابستان 1390)

To investigate the effect of four growth regulator herbicides in various stages of wheat growth, two field and one greenhouse experiments were conducted in Tehran and Golestan provindes.Treatments included 2,4-D (20% SL), 2,4-D+MCPA (67.5% SL), Bromicide MA (bromoxynil+MCPA) 40% EC each at 1.5 L/ha and Duplosan Super (dichlorpop-P+mecoprop+MCPA) 60% SL at 2.5 L/ha applied at the following growth stages of wheat: First tiller (Zadoks 21), last tiller (Zadoks 29), second node (Zadoks 32), and boot swollen (Zadoks 45). In the greenhouse, early milky (Zadoks71) stage was also applied. Field experiments were randomized complete block design with 4 replications, while in the greenhouse, the experiment was in the form of completely randomized design with 5 replications. Data recorded included, yield and yield components. Results indicated that 2,4-D, 2,4-D+MCPA and dichlorpop-P+mecoprop+MCPA may be applied safely at the stages of first tillering up to the second node (Zadoks 21 to 32). Bromoxynil+MCPA was safe to be applied at any stage of growth (Zadoks 21 to 45). In Varamin, none of the treatments caused any damage to the crop.

To investigate interaction of herbicide and nitrogen on wheat and Lepyrodiclis (Lepyrodiclis holosteoides Fenzl.), a research was conducted at two different locations (Shahriyar and Karaj Regions) in RCBD with factorial arrangement and three replications. Research factors consisted of (i) Nitrogen application time (10 days before and 10 days after herbicide application), (ii) nitrogen rates (0, 30, 60 and 100% of the recommended dose, 150 kg ha-1 as urea source), and (iii) herbicide Sulfosulfuron 75% + Metsulfuron-methy 5% (Total®, UPL, India) rates (0, 30, 60 and 100% of the recommended dose, 40 g ha-1). Results obtained from the nitrogen-before-herbicide treatment indicated that when 150 kg ha-1 nitrogen was utilized before application of herbicide (less than 10 g ha-1), Lepyrodiclis seed No. increased up to 50000 m-2; however, an increase in the above herbicide dose (i.e. more than 10 g ha-1) had an adverse impact, that is to say, Lepyrodiclis seed No. drastically reduced. With application of nitrogen after herbicide utizilation (less than 10 g ha-1), it was found that Lepyrodiclis seed No. of both under study regions reduced. An increase in herbicide dose to more than 15 g ha-1 together with the increase of before-herbicide nitrogen application led to the reduction of Lepyrodiclis’ dry matter from 1200 to 300 g m-2. Increase of herbicide dose and also that of nitrogen applied before and after herbicide produced more wheat yield and yield components. An increase in nitrogen dose, particularly when it was applied after herbicide, aggravated herbicide efficacy in Lepyrodiclis control; the reason could be attributed to the nitrogen_herbicide interaction. Therefore, it could be concluded that benefiting from sufficient nitrogen and light, wheat produced more seed yield (6700 kg ha-1), compared to no-nitrogen/herbicide conditions (500 kg ha-1). Further, results revealed that an increase in nitrogen rate, particularly in that of after-herbicide application, left positive effect on herbicide efficacy in Lepyrodiclis control in a way that we achieved the goal (Lepyrodiclis control) with reduced herbicide dose.

In order to approve show potential of Lepyrodiclis (Lepyrodiclis holosteoides Fenzl.) in the winter wheat fields and evaluation of its growth parameters under different light intensities and nitrogen rates, an experiment was conducted at Shariaty Technical University on 2010. Experiment was carried out in a completely randomized design with factorial arrangement and four replications. Experimental factors were different nitrogen rates including 0, 30, 60 and 100% of recommended for wheat (150kg.N.ha-1 from urea source) and light intensity including 25, 50, 75 and 100% of PAR. Results indicated that increased levels of nitrogen and radiation from 25 and 30% to 100%, increase dry weight from 1 up to 8 g.plant-1, number of tillers. From 1 up to 5 and seed no. from 50 up to 250 per plant. Tissue nitrogen percentage of lepyrodiclis increased with increasing in light intensity and nitrogen rate but plant height was reduced from 40 to 10 cm due to increased length of internodes. Plant response as dry weight, tiller no., seed no., plant height, and absorbed nitrogen to light intensity was more than nitrogen rates. According to our findings of this study, in a dense population of wheat where light density is low, and nitrogen level is high, the dry weight of lepirodiclis increases and will produce a high number of seeds, thus contaminating the ground for the next season.

Ceratocarpus arenarius is one of the problematic and noxious weeds in dryland farming of wheat, barley, lentil and peas in North Khorasan. In order to identify the effective treatments in dormancy breaking and determine the effects of light, temperature and pH on germination of this species, experiments based on CRD with 3 replications were conducted in the Research Laboratory of Birjand Faculty of Agriculture during 2009. Results showed that, all treatments except pericarp removal by hand and sulfuric acid (96%) had no considerable effect on dormancy breaking, indicating that the pericarp is responsible for Ceratocarpus seed dormancy. Ceratocarpus seed had identical germination in either light/dark or continuous dark regimes, indicating this weed species is non-photoblastic. Ceratocarpus seed germinated over 35% in the range of alternating day/night tested temperatures (10/5, 20/10, 25/15, 30/20 and 35/25ºC) and the maximum germination (96.6%) was observed at 25/15ºC. Ceratocarpus average germination percentage was about 80% over a pH range of 4 to 10. The maximum and minimum germination occurred at pH 8 (96.6%) and pH 4 (45%), respectively. The information of this study would be useful for the improvement of this weed species management programs.

In order to study of cover crops effects on weed suppression in sugar beet, an experiment was performed in Iranian Research Institute of Plant Protection (Karaj Station), in 2007. The experiment was arranged as completely Randomized Blocks Design with four replications and seven treatments. The treatments were different cover crops (including: Wheat, barley, triticale and rye) that planted between rows. Chemical weed control, weedy and weed free plots were also used as controls. Cover crops were removed by herbicide application (paraquat at 400 g ai ha-1). Phenmedipham+ desmedipham+ethofumesat (Betanal Progress A.M, EC 27.4%) was also used in the four-leaf stage of sugar beet. Results indicated that cover crop treatments suppressed major weeds (Amaranthus retroflexus L. and Chenopodium album L.) and were similar to recommended chemical control (application of herbicide). In addition, total of weed biomass was decreased in barley, rye and control treatments. The minimum biomass of total weeds belonged to the barley+herbicide treatment. Because of synergism effects, barley+herbicide had maximum of the root and sugar yield (29.83 and 4.47 T ha-1, respectively), that was significant with other treatments. In overall, barely cover crop had the most effects on sugar concent. Therefre, sowing winter cover crops between rows for seedbed prepared in autumn (barley, rye, wheat and tritical, respectively) will suppress the dominant weeds and increase the quality and yield of sugar beet.

In order to investigate the effect of different summer cover crops on weed dynamics, an experiment was carried out based on Randomized Complete Blocks Design with 7 treatments and 3 replications. The experiment was performed at Islamic Azad University of Amol (Komdarreh region) during 2009. Treatments included white bean (Phaseolus vulgaris), red bean (Phaseolus vulgaris), cow pea (Phaseolus vulgaris), pinto bean (Phaseolus vulgaris), mung bean (Vigna radiate), lentil (Lens culinaris), and common pea (Cicer arietinum). Some cover crop and weed parameters such as dry weight of grass and broadleaf weeds in each plot as well as dry weight of cover crops were determined. A cover crop/weed biomass ratio (CCW Index) was applied to determine the efficiency of different cover crops in terms of weed depression. Accordingly, weed growth in cowpea and mung bean plots was greatly reduced (CCWI=10.25 and 4.13, respectively) and lentil could not compete with weeds (CCWI= 0.14) and weeds were dominated in lentil plots. In first stage three cover crops common pea, cow pea and mung bean had the most leaf area but white bean in second stage had the most leaf area among cover crops. In first and second samplings cow pea had the highest dry weight (37.33 and 322.2 gr.m-2) and the least dry weight belonged to mung bean and lentil in second and first sampling, respectively. There was a negative and exponential fit relationship between weed dry weight and cover crop dry weight.

An experiment were conducted to find out the proper herbicide and stage of wild barley (Hordeum spontaneum) for chemical control during two years (2009 -2011). Trial was conducted by 9 treatments and 4 replications under RCBD in Fars Agricultural Research Center (Zarghan). Treatments included sulfosulfuron (Apyros 75 WG) and sulfosulfuron 75% + metsulfuron-methyl 25% (Total) at different phenological stages of wild barley (Three leaves unfolded and second node detectable). Plot size was 5 × 6 m. Untreated plots were arranged close to each treated plots. Analysis of variance showed significant difference among treatments, while effects of year and year ´ treatment were not significantly different. Mean comparison remarked that Apyros 30g/h and Total 45g/h at Zadoks: 32 ranked first. The most sensitive stage of wild barley was the second node detectable which responsed effectively to herbicides. Wild barley did not response effectively to herbicides in early phenological stages (Zadoks:13). It was recovered during growing season.

In order to study the effect of pre-harvest application of paraquat on yield and seed quality of canola, an experiment was conducted in Lorestan and Mazandaran during 2006-2007. The experimental design was factorial randomized complete blocks with 3 replications and 10 treatments. Treatments included three doses of paraquat (1.5, 2 and 2.5 L/ha) and three dates of paraqat application (early, on time and late physiological maturity stages of canola), and check (no paraquat application). Results indicated that there was no difference among doses or dates of paraquat application in yield, extracted oil and rapeseed seed germination. There was no difference between the results of two locations of the experiment. Because the population of cruciferous weeds in Lorestan was low, no significant difference of erucic acid content of the extracted oil was observed among treatments. On the other hand, due to the high population of Sinapis arvensis in Mazandaran, the erucic acid content of the extracted oil in paraquat treated plots was lower than in the check plots.