IRANIAN JOURNAL OF WEED SCIENCE
Year:2008 | Volume:4 | Issue:2|Papers Count:9

Wild mustard (Sinapis arvensis L.) and other brassica weeds are important in oilseed rape fields which, in addition to lowering yields, will adversely affect extracted oil quality. In this trial, efficacy of isoxaben (Cent 7, 12.5%SC) to control brassica weeds (in particular wild mustard), and other broad leaf weeds in oilseed rape fields of Hamedan and West Azarbaijan (with cold climate), was tested in a two-year experiment. The experiment was Randomized Complete Block Design with the following seven treatments in 4 replications: 0.4 and 0.5 L/ha of isoxaben used post emergence before rosette stage of Sinapis arvensis, alone or plus trifluralin (Treflan 48% EC) at 2 L/ha, trifluralin at 2L/ha, Weedy and weed free checks. Weed number, dry weight of weeds and oilseed rape yield were the data collected to compare treatments. Results showed that although, at best, Brassica weeds were controlled below 50%, and other broad leaf weeds under 60%, but a yield increase of 58% was observed. Therefore, It was suggested that use of 0.45 L/ha of isoxaben (post emergence) +2 L/ha of trifluralin (pre plant incorporated) could be a recommendation for weed control in oilseed rape of cold regions.

In order to investigating the effect of weeding time on the species composition, plant density, dry weight and physiological characteristics of weeds in corn (Zea mays (L.) cv. SC 704), a field study was conducted at Sari Agricultural Science and Natural Resources University in 2006. The experiment consisted of 14 treatments which laid out in a randomized complete block design with 4 replications. The treatments included weed free and weed infested period to 4th leaf (V4), 6th leaf (V6), 8th leaf (V8), 10th leaf (V10), 14th leaf (V14), tasseling (T) and harvest stages (Full season weed infestation and weed control were the checks). Results showed that weeds density increased when weeds were allowed to grow until corn V8 stage and decreased after this stage, however, weeds could affect on corn plants because of increasing their dry weight and competitive ability. Results showed that weeds density and dry weight significantly decreased with increasing of weed control period length. Generally, velvetleaf (Abutilon theophrasti) with density around 50 percentage of total weed density during growing season has recognized as dominant weed and highest percentage of leaf index in weed infested period related to velvetleaf.Result indicated the peak competition period of weeds in corn crop was between V4 to V10 stages, thus if the weeds are controlled within this period, corn yield would be protected against a significant seed yield reduction.

To evaluate the interaction of nitrogen rates and Nicosulfuron dosages on corn weeds and corn yield, a factorial experiment based on randomized complete blocks design was conducted at Research Fields of University of Tehran in 2009. The nitrogen application rates were 0, 180, 270 and 360 kg ha-1 with nicosulfuron herbicide being applied at 0, 20, 40, 60 and 80 g ai ha-1.Each treatment combination was replicated three times. The result illustrated that all weed spices, except Russian Knapeweed (Acroptilion repens) showed a positive response to the highest level of nitrogen fertilizer (i.e 360 kg ha-1) where weeds dry weights increased markedly. The lowest weed biomass production was observed with herbicide dosages of 60 or 80 g ai ha-1 and nitrogen application rate of 180 or 270 kg ha-1. The more nitrogen fertilizer used (i.e.360 kg ha-1), the higher herbicide dosages needed to effectively control the weeds as more resource might be available for their growth. The responses of corn yield to N rate and herbicide dose were similar to those of weeds as there was a close relationship between weed biomass productions and corn yields. Overall, given the economical costs and environmental consequences of fertilizer and herbicide applications, one may recommend a N application rate of 270 kg ha-1 with 60 g ai ha-1 nicosulfuron in terms of both acceptable weed control (almost 85%) and obtaining a high corn yield (almost 11000 kg ha-1).in additional to achieve 11000 kg ha-1 should use 180 kg ha-1 N fertilizer with 70 g ai ha-1 or 360 kg ha-1N fertilizer with 80 g ai ha-1

experiment was conducted at the research field of Faculty of Agriculture, Ferdowsi University of Mashhad in three replications. Main plots were the application of animal manure at 40 t ha-1 and no application, and subplots included sulfosulfuron application dose (recommended and 30% overdose). The bioassay test using sunflower, canola, soybean, bean, pea, lens, sorghum, barley, corn and sugar beet was set at 98 days after the herbicide application in greenhouse conditions. Results showed 24 days after seeding in the pots the most sensitive crop based on dry weight per plant was canola which had lower weight in the un-amended soil or higher application rate. Soybean and lens were the next sensitive crops respectively. The damage symptoms of the herbicide included roots stunt, chlorosis and epinasty in the shoots were more obvious in bean, soybean, sugar beet and canola.

The effects of environmental factors on germination and longevity of downy brome seeds were examined in laboratory and field experiments. Downy brome could germinate in a broad range of temperatures (15/6, 20/10, 25/15, 30/15, and 35/20oC). The germ inability, however, was different depending on the temperature range and the results showed that the highest germination was occurred in 20/10ºC (91%) under continuous dark regime, while the lowest germination percentage was observed in 35/20ºC (5%) under light/dark conditions. Salinity showed significant adverse effect on germination of this weed, so that the highest germ inability was at 0 concentration of NaCl (89%).Increased salinity levels significantly decreased downy brome germination and its germination completely ceased at 320 mM NaCl. This study indicated that increasing pH in the range of 4 to 8 resulted in enhanced germination percentage, while further increase of pH significantly reduced germ inability.Another experiment in which seeds were after-ripened at different depths in the field showed that increased burial depths from 0 to 10 cm accelerated seed after ripening and the lowest germination occurred in the seeds which were placed on the soil surface.

Water and nitrogen are the most important factors in plant competition. Since of nitrogen uptake by plants depend on water mass flow, and competition for nitrogen is depend to water availability in soil. In order to study the effect of drought stress and nitrogen application rate on corn-redroot pigweed interaction, a factorial experiment was conducted under greenhouse condition based on replacement series method in which different planting ratios of pigweed and maize component of 0: 100, 25: 75, 50: 50, 75: 25 and 100: 0 pigweed: corn to corn tease ling stage in 1388 year at Faculty of Agriculture, Ferdowsi University of Mashhad research greenhouse. Treatments included soil water availability in soil at 2 levels (25 and 50 FC) and nitrogen application rate at 3 levels (0, 200 and 400 kg per hectare). Results showed that both corn and pigweed dry mater increased significantly (p£0.05) with increasing nitrogen application rate in normal soil water condition. It also enhanced corn competitive ability with pigweed. But drought stress decreased both plants dry mater production of both corn and pigweed with nitrogen application. It also had not any advantage for corn yield.

The presence of weed in soybean is a serious threat to crop yield. Little research has addressed multiple weed species interference in soybean. Field experiments were conducted at the Research Farm of University of Tehran, Karaj, Iran, during the growing season of 2007 and 2008 to determine the influence of density of single and multispecies populations of common cocklebur and redroot pigweed on soybean yield and competitive abilities of weeds. Common cocklebur and redroot pigweed seeds were sown concurrently with soybean and established at selected density within 15 cm on either side of soybean row. The experimental design was factorial based on randomized complete block design with three replications. Results showed that soybean grain yield was significantly affected by weed competition. Soybean yield loss due to competition was 86% and 70% in first and second experiment, respectively. Soybean yield was affected more by common cocklebur than by redroot pigweed. Common cocklebur at a density of 2.3 (in 2007) and 6.25 (in 2008) plants per m-1 of row reduced soybean yield by 50%. In contrast, same reduction in soybean yield from redroot pigweed was obtained at density of 5.9 and 12.1 in 2007 and 2008, respectively. Competitive effect of common cocklebur was equivalent with 2.37 and 1.91 plant of redroot pigweed density in 2007 and 2008, respectively.

An outdoor pot-experiment was conducted to evaluate the effect of various fertilizers on reduction Phelipanche aegyptiaca damage in tomato at Research Farm of University of Tehran, Karaj, during 2008 and 2009.Experimental design was a randomized complete block with four replications.Treatments comprised ammonium nitrate, ammonium phosphate and urea each at rates of 150 and 300 kg/ha and ammonium sulfate at 250 and 500 kg/ha. In this research control pot for the first year was sowing Phelipanche aegyptiaca seed and in the second year, control without Phelipanche aegyptiaca seed also was included. Results in the first year showed that Ammonium sulfate applied at 250 and 500 kg/ha and control without broomrape was the most effective treatments in increasing tomato yield and reducing broomrape damage. Ammonium phosphate and urea both at 150 kg! ha and ammonium sulfate at 250 kg/ha had most tomato dry weight while the minimum was belonged to ammonium nitrate used at 150 and 300 kg/ha. Ammonium phosphate applied at rates of 150 and 300 kg/ha decreased aerial and tuber dry weight of broomrape more than other treatments. According to these results applying ammonium sulfate at 250 kg/ha for broomrape control in tomato is the best treatment.

Field experiment was carried out during 2008 growing season at the research farm of University of Tehran, Karaj, Iran, to evaluate the interference effects of redroot pigweed (Amaranthus retroflexus L.) on light interception and RUE of four Sesame cultivars. Experimental design was a randomized complete block with three replications per treatment. The first factor was the sesame cultivars including, Otlan (Multiculum), Varamin 2822, Naz Uniculm and Karaj 1 (Uniculm cultivars). The second was the redroot pigweed density at five levels: 0, 2, 4, 8, and 16 plant m2. The results indicated that leaf area distribution in the canopy has a triangular function and the height, in which maximum leaf area redroot pigweed was observed, was not the same among treatments. Light interception by sesame cultivars under redroot pigweed interference decreased by 12, 47, 32, and 42 percent for Oltan, Varamin 2822, Naz Uniculum and Karaj I, respectively, compared to control. Redroot pigweed interference reduced RUE by 18.6, 35, 27.7, and 21.7 percent for Oltan, Varamin 2822, Naz Uniculum and Karaj 1 respectively, compared to control. The highest RUE was observed in Oltan cultivar.