نشریه دانش علفهای هرز
سال نهم شماره 2 (بهار و تابستان 1392)

In order to investigate the efficiency of non-chemical methods management of weeds in forage Sorghum، an experiment was conducted in Varamin Research farm during 2010. The experiment was carried out in split factorial design with three replications. Treatments included cultivation at 3 leaf stage of sorghum، cultivation at 3 and 5 leaf stages of sorghum، weed free and weed infested as main plots and two levels of sorghum densities (190000 and 266000 plant/ha) and two levels of sorghum planting patterns (one and two row plant pattern) as factorial treatments in subplots. Weed density and biomass were measured 30 days after second cultivation and before second forage harvesting. Forage biomass was also measured at each harvesting. According to the results، weed density was decreased by cultivation (about 50%) but as the density of weed was very high، the effect of cultivation on weed biomass was not significant. Increasing density of sorghum+ two row planting pattern had positive effect on the final yield of sorghum. In general، integrating cultivation، density and planting pattern did not have significant effect on the final yield of sorghum and weed population، but the effects of cultivation at 3 leaf stage of sorghum + two row planting pattern and 19000 plant/ha+ two row planting pattern) on final yield were more favorable than other treaatment. It seemed that these treatments can be recommended in integrated weed management of sorghum.

In order to investigate the efficiency of non-chemical methods management of weeds in forage Sorghum، an experiment was conducted in Varamin Research farm during 2010. The experiment was carried out in split factorial design with three replications. Treatments included cultivation at 3 leaf stage of sorghum، cultivation at 3 and 5 leaf stages of sorghum، weed free and weed infested as main plots and two levels of sorghum densities (190000 and 266000 plant/ha) and two levels of sorghum planting patterns (one and two row plant pattern) as factorial treatments in subplots. Weed density and biomass were measured 30 days after second cultivation and before second forage harvesting. Forage biomass was also measured at each harvesting. According to the results، weed density was decreased by cultivation (about 50%) but as the density of weed was very high، the effect of cultivation on weed biomass was not significant. Increasing density of sorghum+ two row planting pattern had positive effect on the final yield of sorghum. In general، integrating cultivation، density and planting pattern did not have significant effect on the final yield of sorghum and weed population، but the effects of cultivation at 3 leaf stage of sorghum + two row planting pattern and 19000 plant/ha+ two row planting pattern) on final yield were more favorable than other treaatment. It seemed that these treatments can be recommended in integrated weed management of sorghum.

Weed leaf area damage coefficient (λ) denotes the increase in weed competitiveness per unit increase in its leaf area. Although the variability of this parameter has been confirmed، it was assumed to be constant in many researches. The objective of this study was to determine the interactions between herbicide dose and λ. Field experiments were conducted to determine the relationship between competitive indices of maize، Xanthium strumarium and Amaranthus retroflexus during 2007 and 2008. Five doses of the herbicide nicosulfuron as main factor، and 16 density combinations comprised of 4 densities of A. retroflexus × 4 densities of X. strumarium as sub plots were arranged in a one-replicate split factorial. For A. retroflexus، the λ value was constant. For X. strumarium، the λ value was constant with no herbicide and 0. 25 rate of the full dose. With increasing the dose up to half the recommended dose، the λ value increased and again with increasing dose to 0. 75 rate، it returned to the level with no herbicide. This relationship was properly described by Gaussian model. Herbicide at half rate probably removed the apical dominance and increased the number of lateral shoots. Herbicide as an external factor was the most important determinant in the change of X. strumorium canopy shape. Deep understanding of the system behavior، relations and interactions with herbicide applications is of great help in improving the predictive power of weed management models

To study the resistance of wild musturd populations to acetolactate synthase inhibitors، 31 suspicious wheat fields to resistance (included of 14، 12 & 5 fields located in Golestan، Khoozestan & Keramanshah، respectively) were studied during 2012. Some important management information was analyzed in the first part of experiment. In the second part، the effect of three acetolactate synthase inhibitor herbicides (ALS) including of Tribenuron methyl (Granstar)، sulfosulfuron + metsulfuron-methyl (Total) and Iodosulfuron methyl sodium+Mesosulfuron Methyl+Mephen payer (Atlantis) on the growth of suspicious populations was examined on the base of complete randomized block design. To study dose-response reactions، different doses of mentioned herbicides were sprayed on resistant populations (G3، G4 & G5 of Gorgan، Kh1، Kh5 & Kh7 of Khoozestan and Ker1 of Kermanshah) and three sensitive populations (G9، Kh3 & Ker1 of mentioned province) in the third part of this experiment. According to the results of the first part، the only crop sequence of herbicides was not observed in more than 80% of the fields and wheat was cropped as in 39% of these fields. In addition، Khoozestan had the weakest crop rotation with 50% single cropping. The results of second part showed that 20% and 10% of populations were resistant to Tribenuron methyl and sulfosulfuron + metsulfuron-methyl respectively، but، high resistance to Iodosulfuron methyl sodium+Mesosulfuron Methyl+Mephen payer. Also، 10% of populations were resistant to Tribenuron methyl and sulfosulfuron+metsulfuron-methyl. According to the results of dose-response experiment، G3، G4، G5 (Golestan) and Kh7 (Khoozestan) populations had low، Ker2 (Kermanshah) had medium and two populations of Kh1 and Kh5 (Khoozestan) had high resistance to Tribenuron methyl. In addition، Kh5، Kh7 (Khoozestan) and G3 (Golestan) had low، medium and high resistance to sulfosulfuron+ metsulfuron-methyl، respectively.

In order to evaluate the effect of nitrogen، plant density and weeds on growth and yield of wheat cv. Shiraz، an experiment was conducted during 2009/2010 and 2010/2011 growing seasons at Agricultural College of Shiraz University. The experimental design was split-split plot with main plots arranged as an RCBD with three replications. Treatments included weed and weed free as main factor، three nitrogen levels (50،100،150 kg ha-1) as sub factor and seeding rate (180، 225، 270 and 315 kg ha-1) as sub factor. Wheat growth and yield as well as its components (1000-grain weight، grain number per spike and ear number m-2) were affected by weeds so that grain yield was significantly reduced by 34. 23%. With increasing level of nitrogen (from 50 to 150 kg/ha)، wheat grain yield (3840 Vs 4980 kg/ha) was significantly increased by 29/83%; however weed dry weight was also increased in weedy plots indicating that additional nitrogen cannot compensate for the effect of weed competition. Increasing seeding rate recorded significantly higher yield and yield components than control and a simultaneous reduction in weed competition with the lowest weed dry weight was achieved at 315 kg ha-1 seeding rate. A rise of nitrogen rate increased (0. 57 gr m-2) weed dry weight. There was a negative and significant correlation between seed yield and weed dry weight، so that under different nitrogen levels، increasing weed dry weight decreased seed yield. Generally، it appears that compared to increased rate of nitrogen، higher seeding rate is a more effective strategy to compensate for yield losses caused by weeds. To achieve optimal wheat yield، application of 270 kg wheat seed and 150 kg nitrogen ha-1 is recommended.

This study was conducted to investigate enhancement effects of additives on efficacy of glyphosate at different levels of water hardness on camelthorn control at Abasabad Research Station (Mashhad) during 2009-2010. Two separate experiments were carried out. In the first experiment، Four doses of glyphosate (Rundup SL %41) i. e. 0، 4، 6 and 8 L. ha-1 were separately tank mixed with 0. 1، 0. 25، 0. 5 percent of X-change at three levels of water hardness including 47. 5، 95 and 190 mgL-1 of Mg+2 + Ca+2. In the second experiment، ammonium sulfate at three levels i. e. 0، 3 and 4 percent replaced X-change while other treatments remained intact. Treatments were applied during early May to camelthorn plants. Each treatment was replicated three times. Results revealed that without applying additives to herbicide solution، glyphosate efficacy to reduce plant height was significantly declined at higher levels of water hardiness as ED50 was increased from 2. 478 to 31. 407 L. ha-1. Maximum glyphosate efficiency was observed when X-change was used with concentration of 5%. It could reduce ED50 to 6. 579 L. ha-1 compared to 31. 407 L. ha-1 where no additive was applied at highest level of hardness. Under low and medium ED50، there was no significant difference between xchange and ammonium sulfate.

To study the effect of different levels of nitrogen and intercropping systems of basil (Ocimum basiilicum L.) and cowpea (Vigna unguiculata L.) on weed population structure، an experiment was carried out as a split-split plot a randomized complete blocks design with three replications during 2010-2011 at Sari Agricultural Science and Natural Resources University. Treatments included weed control and weed infested as the main plots، levels of nitrogen (0، 50 and 100 kg/ha) as sub plots، Sole cropping of cowpea and basil، and additive planting ratios of 25، 50 and 75% basil as sub-sub plots. Under weed control conditions، the highest yield of cowpea (685 kg ha-1) and maximum dry matter yield of basil (430 kg ha-1) were obtained from 50% basil ratio with 50 and 100 kg ha-1N fertilizer application، respectively. The highest yield of basil (139 kg ha-1) was observed in weed infested plots of 25% basil planting ratio and 100 kg ha-1 nitrogen fertilizer with the highest invasive coefficient of 1. 66 and competition coefficient of 3. 42. The highest land equivalent ratio (1. 43) belonged to 50% additive ratio of basil in weed free and the lowest (0. 87) belonged to 75% ratio and without nitrogen fertilizer in weed infested condition. Generally، existence of cowpea in additive intercropping reduced the population and biomass of weeds compared to basil sole cropping. Increasing nitrogen fertilizer application caused faster closed canopy of plant species in intercropping which led to reduced weeds population and biomass.

In order to evaluate the effect of some herbicides for weed control in established alfalfa، an experiment was conducted in a randomized complete blocks design with 4 replications in the Agricultural Research Center of Jiroft، for two years from 2009 to 2011. Treatments included Pursuit (imazethapyr SL 10%) at 0. 4، 0. 6، 0. 8 and 1 Lit/ha plus cytogate at 1 Lit/ha، plus Focus (cycloxydim EC 10%) at 2 Lit/ha، Stomp (pendimethalin EC 33%) at 2. 5 and 3 Lit/ha، Bazagran (bentazon SL 48%) at 3 L/ha plus focus at 2 Lit/ha، Senkor (metribuzin WP 70%) at 1 kg/ha، Butress (2،4،DB 42. 3 % EC) at 2، 2. 5، 3، 3. 5 li/ha and weed- free as a check. The effect of herbicides on alfalfa biomass and weed biomass and density was studied from 3 harvests. Herbicides had significant effect on the density and biomass of bermudagrass (Cynodon dactylon) and field bindweed (Convolvulus arvensis). Herbicide cycloxydim، at 2 L/ha، was best to control bermudagrass، reducing density by 47-64% and dry weight by 47-62%. The best treatment to control field bindweed was 2،4-DB at 3. 5 L/ha، reducing density by 38-42% and dry weight by 36-39%. The highest alfalfa yield was obtained with imazethapyr at 0. 8 and 1 L/ha plus cytogate at 1 Lit/ha، plus cycloxydim at 2 Lit/ha.