مجله پژوهش علف های هرز
سال دوم شماره 2 (پاییز و زمستان 1389)

In order to assess the response of weeds to a number of different rotations, a six-year experiment was conducted based on a randomized complete block design with four replications at Agricultural Research Station of Khorasan Razavi, located in Jolgeh Rokh. Experimental treatments included: vetch-potato, canola-potato, barley-potato and fallow-potato (control). Each rotation was repeated three times during the 6-year period of the experiment. The results indicated that canola-potato rotation proved highly successful in controlling weeds during the growing season. The highest density of perennial weeds was observed in the fallow-potato rotation. The barley-potato rotation made an appropriate control of the weeds. The majority of weeds observed in sampling were spring annual ones, with lambsquarter and pigweed being the dominant species. In conclusion, this research showed that the best appropriate rotation in each area could be use in sustainable management of weed control.

A field experiment was carried out during 2003-2004 growing season at research field of Sugar Beet Seed Institute (SBSI) in Karaj, to study the integrated post-emergence weed control methods in the system of sugar beet seedbed preparation in autumn. The experimental design was split-split plot based on a randomized complete block design with four replications. The main plots consisted of using and non-using cultivation for weed control at eight leaf stage of sugar beet and the sub plots of nine post emergence herbicide, the sub-sub plots of hoeing and no hoeing in their thinning stage. Plant population of weed species was determined before and after herbicide application and their dry weights at harvest time. The results in the system of sugar beet seedbed preparation in autumn indicated that hoeing in the thinning stage of sugar beet was not affected on the post emergence weeds, presumably due to winter weeds residue on the soil surface as mulch. Among the herbicides, split application of the Triflusulfuron + Phenmedipham+Desmedipham+Ethofumesate and also the Cloridazon + Phenmedipham+Desmedipham+Ethofumesate both had the most efficiency in controlling the post-emergence weeds. Thus, they can be considering as the most effective sugar beet herbicides. In the method of complete seedbed preparation in autumn, when sugar beet canopy catches good ground cover, cultivating at eight leaf stage of sugar beet will not control significantly post emergence weeds.

Two laboratory experiments were conducted to determine the inhibitory effects of wild barley (Hordeum spontaneum Koch) plant parts on germination and seedling growth of wheat (Triticum aestivum L. cv. Pishtaz). Aqueous extracts were separately made from mature wild barley leaves and culms. Leaf and culm extracts and mixture of the two, significantly decreased wheat seed germination. The reduction of wheat seed germination due to leaf extract was more than those of culm and mixture of the two. Wheat shoot and root lengths were also significantly inhibited by leaf and culm extracts and mixture of the two. Generally, leaf extract exerts more inhibitory effects on wheat germination and seedling growth than that of culm and/or mixture of the two. In the second experiment, wild barley seedlings were harvested at 1, 2, 3, and 4-leaf (L1, L2, L3, and L4, respectively), and tillering stages and aqueous extracts were made from each plant part at said stages. Wheat seed germination was severely inhibited by extracts made from L1, L2, and L3 stages. Extracts made from L4 and tillering stages significantly reduced wheat seed germination. Wheat shoot and root lengths were also significantly decreased by extracts made from all growth stages of the weed. Extracts made from L1, L2, and L3 stages exerted the same effects on wheat shoot length, whereas, for wheat root length, these treatments caused significant inhibition. Extracts made from L4 and tillering stages also significantly reduced both wheat shoot and root lengths. The results showed that inhibitory effects of extracts tend to lower with plant age.

To obtain pathogenic fungal isolates from Physalis divericata L., the plants showing the symptoms of fungal diseases were collected from different areas in Lorestan and were transported to the laboratory in year 2009. The samples, after surface disinfection, were cultured on PDA and V-8 media. Based on fungi keys identification, two species including Alternaria alternata and Fusarium sp. were identified. The pathogenicity and virulence of identified fungal pathogens at 105, 106, 107 and 108 spores per mL of distilled water were tested on Physalis divericata at different growth stages (cotyledon, 4, 6 and 9-11 leaf). Host range tests were conducted on beans, corn, sugar beets and soybeans under greenhouse conditions. Results showed that Alternaria alternata isolate A6 induced more severe disease than other Alternaria isolates and Fusarium sp. Physalis divericata was more sensitive to Alternaria alternata isolate A6 at 6 leaf-stage, especially at 108 spore per ml distilled water. Non of the target crops showed any symptoms due to inoculation by Alternaria alternata isolate A6.

Laboratory and greenhous studies were conducted to determine the allelopathic potential of six common weeds of Golestan pastures and fields on wheat seed germination and seedling growth. shoot extracts of italian cocklebur ¬(Xanthium strumarium L.)¬, Russian knapweed ¬(Acroptilon repens (L.) DC.), andhairy fleabane ¬(Conyza bonariensis (L.) Cronq.), reduced wheat seed germination by 42%, 47%, and 20% respectively, when companed to the check treatment. However, allelopathic effects of shoot extracts of the low concentration caused an increase in wheat root dry weight, but higher concentration reduced shoat dry weight significantly. Root extracts of hairy fleabane, Russian knapweed, and cocklebur at the lower concentration stimulated length and dry weight of wheat root, but at the higher concentration root length and dry weight were reduced significantly. The result of greenhouse experiment showed that the shoot residuces of each one of the three weeds of both lower and higher concentration reduced root length and shoot length and dry weight of wheat and this reduction was significant for the higher concentration. Among the three weed, Russian knapweed extract showed strong activity and can be a promising natural product to be used as a herbicide in future.

An experiment was carried out as RCBD with three replicates in order to assay the competition of wheat cultivars with four weed species (Sinapis arvensis L., Descurainia Sophia (L.), Hordeum spontaneum C.Koch and Avena fatua L.). Tow wheat cultivars with different competitive power were studied. Pishtaz was resistant one and Tabasi was sensitive cultivar. In addition 3 densities of each weed (0, 2 and 4 plants per pot for Sinapis arvensis and 0, 4 and 6 plants per pot for others) in tow positions (as a target and neighbor plant) were evaluated. Results showed that plant height increased in Pishtaz cultivar as weed density increased but there was not any significant effect on Tabasi cultivar. Wheat leaf area and biomass reduced in competition of weeds specially Sinapis arvensis.

In this research, the efficacy of a few sugar beet selective herbicides in conventional and minimum tillage systems was evaluated in Shahre-kord area, Iran, in 2008. For conventional tillage, at the end of April, a deep tillage up to 35 Cm was carried out using marl bow plow, but for minimum tillage, no soil disturbance was done. Then, sawing bed was prepared by a cyclotiller with a shallow tilling. The herbicides were applied using a knapsack sprayer equipped with a t-jet nozzle when sugar beet was at 4-leaf stage. The results indicated that, apart from herbicide applications, the number and dry weight of barnyard grass and Anchusa sp. in minimum tillage was significantly less than that of conventional tillage. Tillage systems were not significantly different in the number and dry weight of redroot pigweed. For controlling redroot pigweed and Anchusa sp., application of mixed of metametron and phenmedipham + desmedipham + ethofumesate, respectively at 2800 and 720 g ha-1, were significantly more efficient than tank mixed application of triflusulfuron and phenmedifam respectively at 15 and 314 g ha-1, and clopyralid at 2400 g ha-1. These differences were more pronounced in protective tillage system. But, for reducing the number of barnyard grass plants, the efficacy of tank mixed application of triflusulfuron and phenmedipham in conventional tillage was significantly higher than the other herbicide treatments. But, in protective tillage, due to low population of barnyard grass no significant differences were recognized among the treatments, compared to the weedy check. In both tillage systems, all treatments, compared with weedy check, increased the crop root yield. The highest root yield was obtained in minimum tillage using phenmedipham + desmedipham + ethofumesate or metametron. The treatments had no significant effect on sugar purity of the crop.

To investigate the possibility of biological control of wild mustard, a laboratory and greenhouse study was conducted in 2009-2010 at Azad University Research Station of Khorramabad. The results caused to introduce the Alternaria alternata isolates A7 from fungi Fusarium compactum, Fusarium reticulatum, F. lateritum, F.javanicum and A. alternata, A.giasen, A.radicina as a potential for biocontroling of this weed. Result of this study showed that isolates A7 could significantly reduced dry weight due to increased virulence of fungus in the 6 leaf growth stage were wild mustard.