IRANIAN JOURNAL OF WEED SCIENCE
Year:2014 | Volume:10 | Issue:1 |Papers Count:8

A survey was carried out in irrigated wheat fields to assess the flora changes in the weed communities structures and flora change in Kermanshah province in 2002 and 2012. 85 fields from 11 counties were evaluated. Some population indices such as plant species frequency, density and species dominance were calculated for 2012 and were compared to the values for 2002. Results showed that in 2012, 112 weed species were distributed throughout wheat fields consisting of 18 grass weed species and 94 broadleaves. Convolvulus arvensis, Avena ludoviciana, Sinapis arvensis and Hordeum spontaneum were dominant weed species in 2002. In 2012, the respective species not only were found dominant but also showed 128. 3, 29. 14, 51. 46 and 36. 31 percent increase in dominance index, respectively. In contrast, the weed species Galium tricornutum, Glycyrrhizia glabra, and Phalaris brachystachys, respectively showed 10. 45, 52. 27, and 27. 16 percent decrease in dominance index compared to values calculated for 2002. Forty four new weed species were identified in 2012 that were not observed in 2002. In addition, our observations from the areas out of random quadrates sampling resulted in identifying forty eight new weed species. Shannon diversity index showed no difference from 2002 to 2012 for Kermanshah and Kangavar. Simpson dominance index indicated an increase in weed species evenness in Kermanshah county in 2012.

In an experiment in randomized complete blocks design with four replications and 17 treatments, combinations of trifluralin (Treflan 48% EC) with metazachlor + quinmerac (Butisan Star, 41. 6% SC) were tried to achieve a better control of canola weeds, especially Brassica family in Khuzestan, Golestan, Mazandaran and Fars provinces. Treatments included Treflan at 2 L/ha. ppi + clopyralid (Lontrel, 30% SL) at 0. 8 L/ha. post emergence of broadleaf weeds, Treflan at 1. 5, 2 and 2. 5 L/ha. ppi, Butisan Star at 1. 5, 2 and 2. 5 L/ha., preemergence, combinations of Treflan+Butisan Star at doseges used above, weed-free check. Haloxyfop-R-methyl ester (Galant Super 10. 8% EC) at 0. 75 L/ha was sprayed over the whole experiment to control grassy weeds. Results indicated that In Fars and Golestan, combinations of the two herbicides caused serious injury to canola and the weed control efficacy of herbicide combinations was not much better than Butisan Star alone. In Mazandaran results were similar, but canola did not show injury as a result of herbicide combinations. In Khuzestan, herbicide combinations not only did not damage canola but also had a better control of weeds and increased canola yield. Due to different types of soil in various regions, results varied, and therefore, it was recommended that before applying combination of above herbicides in any new place, they should be tested.

In order to investigate the effects of water deficit and redroot pigweed (Amaranthus retroflexus L. ) interference period on sunflower yield, two field experiments were carried out during 2009-10 and 2010-11 growing seasons at the Agricultural College of Shiraz University. The experimental design was split plot based on randomized complete blocks with three replications. Main plots included water deficit at three levels (100%, 75% and 50% field capacity) and main plots consisted of two groups 1)Interference period of redroot pigweed up to 8-leaf, 12-leaf stages, head emergence, flowering and maturity(whole season interference) of sunflower and 2)Control of pigweed up to stages mentioned above. Results indicated that with increasing water deficit levels from 100% to 75% and 50% field capacity, seed oil percentage, seed yield and its components decreased. With increasing pigweed interference, sunflower yield, and yield components, seed oil percentage and plant height were decreased and these reductions were significant from 12-leaf stage until head emergence. Water stress decreased pigweed dry weight more than crop. Water stress increased pigweed interference, in other words impact of weeds on sunflower growth and yield, increased with water stress.

Greenhouse and field experiments were conducted to investigate the effect of different mechanical cutting methods of the mother plant in an appropriate time on the viability (%), seed size (mm2) and 100 seed weight (g) of Abutilon theophrasti (velvetleaf). Three mechanical cutting methods with considering the different stages of capsule development were used: (1) cutting the entire plant from its base without separation of capsules from mother plant and plant material was left to dry on the greenhouse bench or soil surface for four weeks (EPD) (2) individual capsules were harvested and left to dry on the greenhouse bench or at the soil surface for four weeks (CD), and (3) capsules were harvested and seeds tested immediately for viability(%), seed size (mm2) and 100 seed weight (g) (CF). The flowering phenology of each plant was recorded throughout the experiment. After four weeks, viability (%), seed size (mm2) and 100 seed weight (g) seeds from plants in treatments EPD and CD were tested. In all the mechanical cutting treatments, on plant capsules were classified according their clour in four developmental stages. In both greenhouse and field experiments seeds from the first stage of development were not viable and the viability began to appear during the second developmental stage, and reached to 100% during the third and the later stages of development. In both experiments, the approaching rate of full viability was higher for seeds from capsules that were tested immediately (10 and 7 DAF) in comparison with two treatments of CD and EPD. In the greenhouse experiment viability of the seeds from capsules that were left to dry on the greenhouse bench was higher than that of seeds from entire plant that were left to dry on the greenhouse bench. However, in the field experiment this rate was ranked differently as it was higher for seeds from the entire plant dried at the soil surface compared to the seeds from capsules which were separated and dried at the soil surface. In the greenhouse experiment the size of the seeds from separated capsules was more than the size of the seeds from attached capsules to the entire plant. However, there was not any significant difference between these two treatments in the field experiment. This can demonstrate the rapid drying rate of seeds from detached capsules than the attached ones in the greenhouse experiment which leads to the more viability and survival in the desiccated condition of greenhouse. This difference is likely due to the greater desiccation tolerance of seeds from detached capsules. In the field, opposite trends were observed and may have been due to the wet conditions present at the field site after plants or capsules had been cut. Results of this study showed that mechanical cultivation, mowing or cutting the entire plant (capsules remain attached to the parent plant) during hot months of summer in the areas with less precipitation and splitting the velvetleaf shoot to the small pieces (disk) in the wet area with high precipitation would be an effective management for avoiding viable seed production of velvetleaf. Also these species should be cut before the second stage of development of seed to produce minimum viable seeds.

An experiment was conducted to evaluate yellow nutsedge (Cyperus esculentus L. ) density effects on some rice physiological, morphological characteristics and its paddy yield at Sari Agricultual Sciences and Natural Resources University. This experiment was performed as factorial based randomized complete blocks design with three replications. Weed density in four levels (0, 60, 120 and 180 plants m-2) and rice varieties in three levels (Tarom as traditional cultivar, Shirodi and Ghaem as improved cultivars) were the treatments. Results of ANOVA revealed significant difference of weed numbers, rice cultivars and their interactions on shoot length, flag leaf area, leaf number, leaf wet and dry weight, chlorophyll content, SPAD value, harvest index and paddy yield. Mean comparisons showed that the highest levels of all characteristics were recorded in the control plots, while their lowest levels were observed in weed density of 180 plant m-2. The response of different rice varieties to nutsedge densities varied. Among rice cultivars, Tarom had the lowest slope in flag leaf area equation (y= 33. 22-0. 04x), stem length (y= 105. 33-0. 20x), fertile tiller number (y= 22. 5-0. 03x), harvest index (y= 24. 98-0. 3x) and paddy yield (y= 366. 6-0. 57x). Therefore, this traditional cultivar is recommended as the strongest competitor compared to Shirodi and Ghaem improved cultivars which were shown to be as weak competitors to yellow nutsedge weed.

This study was performed in order to assess the weed species richness in summer crop fields. 21 fields were chosen in Sarableh, Darrehshahr and Dehloran, Ilam province with different climatic patterns during 2009-2010. Their demographic indices were calculated. The geographic information was recorded by GPS for each field. Results showed that 26 weed species can be found in corn fields (main summer crop) of Ilam province. According to abundance index, the most common broad leaf weeds in corn fields were Heliotropium europaeum L., Amaranthus bliotoides L., Convolvulus arvensis L. and Hibiscus trionum L. The dominant grass weeds were Sorghum halpense L. and Echinochloa crus galli L. The highest stability index (77. 77 %) was related to S. halpense and A. bliotoides in corn fields. Therefore, they are the most persistent weeds in these fields. All environmental factors such as climatic condition, and elevation affected weed species richness and structure. The greatest effect on weed species richness was related to crop type and sowing date.

This study was performed to evaluate the efficacy of combination of two pre-emergence herbicides with broad and narrow leaf weed spectrum and four post-emergence herbicides with broad leaf spectrum for use in forage sorghum in three locations (Iran): Mashhad, Ahwaz and Varamin during 2010. The experiment was conducted in a RCBD design with four replications. Treatments consisted of acetochlor (Acenit EC 50%, at 3. 5 L ha-1) and pendimethalin (Stomp EC 33%, 4 L ha-1) as pre-emergence in combination with post application of 2, 4-D+MCPA (U46 Combi Fluid SL 67. 5%), Bromoxinil+MCPA (Bromicide MA EC 40%), 2, 4-D+Dicamba (Dialen Super SL 46. 4%), and Bentazon (Basagran SL 48%) at 1. 5, 1, 1. 5 and 1. 2 L ha-1 respectively and the weed free and weed infested controls. As expected, all treatments were successful in broad leaf weed suppression and therefore increased forage yield comparing to weed infested check. These results showed that all herbicides used in this research can be used alternatively in sorghum. Acetochlor in combination with 2, 4-D+MCPA was the best treatment in weed suppression and yield increase while treatments containing bentazone were weak. Neither acetochlor nor pendimethalin succeeded in Johnsongrass (Sorghum halepense (L. ) Pers. ) suppression while Jungle rice (Echinochloa colonum (L. ) Link) was controlled by these two herbicides. Acetochlor in combination with bentazone were effective in Nutsedge (Cyperus sp. ) suppression but they show some injury on sorghum. This injury did not affect the yield in Mashhad but in Ahwas decreased yield. Since only broad leaf spectrum herbicides were used as post-emergence in this research, more study on post narrow leaf spectrum herbicides for sorghum are recommended.

In order to determine changes in weed flora in wheat fields of Savojbolagh and Shirvan counties, the results of studies in 2000 and 2010 were compared. Based on the first study (2000) in Savojbolagh County, 57 species belong to 19 families and in Shirvan county 28 species belong to 13 families were detected. In second study (2010) in Savojbolagh County, 53 species belong to 19 families and in Shirvan county 53 species belong to 18 families were detected. Some species of flora were removed and some new species were added to the flora. Abundance index of some species were changed, some species lost their dominance and others became dominant. Any change in the dominance index due to changes in frequency, density, or both, can be related to many factors. In Savojbolagh dominance of many species including knotweed (Polygonum aviculare), bedstraw (Galium aparine), lepyrodiclis (Lepyrodiclis holosteoides). speedwell (Veronica camplypoda) and fumitory (Fumaria vaillantii) were due to increase in density but in Shirvan dominance of many species including common lambsquarters (Chenopodium album), hairy vetch(Vicia villosa), (Goldbachia laevigata) and Canada thistle (Circium arvense) were due to increase in density, except for knotweed (Polygonum aviculare) was due to increase in frequency. Any change in the abundance of grass weed species in wheat fields of Savojbolagh indicate that the management methods applied for these species have failed after a decade and winter wild oat (Avena ludviciana) and feral rye (Secale cereale) remain as the dominant grass weed species. Change in abundance index of broadleaf weed species in Savojbolagh and dominance of some species such as knotweed, lepyrodiclis and speedwell showed that change flora of broadleaf weeds was in response to weed management methods. Introduction of new species to the wheat fields of Shirvan was considerable. The management methods applied were clearly the reasons for the floral changes, we should now adopt new strategies to manage the new species.