نشریه دانش علفهای هرز
سال دوازدهم شماره 2 (پاییز و زمستان 1395)

This experiment was conducted to study the residual effect of some wheat herbicides on following corn (Zea mays L.) crop under different tillage systems in Karaj province. Tillage treatments included: conventional tillage, minimum tillage and, no-tillage. Herbicide treatments were: 1- bromoxynil MCPA (EC 40%) 1.5 lit/ha, 2- triasulfuron dicamba (WG 70%) 150 gr/ha, 3- mesosulfuron-methyl iodosulfuron-methyl-sodium (62 WG) 400 gr/ha, 4- metsulfuron methyl sulfosulfuron (w/v %5) 36 gr/ha, 5- tribenuron methyl (EC 8%) clodinafop propargyl (DF 75%) 20 gr/ha and 0.8 lit/ha respectively, as well as unweeded control (without herbicide). Soil sampling for bioassay tests made from surface layer (0-12.5 cm) and, sub-surface layer (12.5-25 cm). Bioassay experiment was conducted with Cress (Lepidium sativum) as a test plant and corn. Cress emergence percentage and cress and corn dry matter and height was assessed. Results indicated that herbicide bio- availability was depended on tillage system; in fact herbicide bio-availability was minimum in no-tillage systems. Triasulfuron dicamba, mesosulfuron-methyl iodosulfuron-methyl-sodium and metsulfuron methyl sulfosulfuron were the most persistent herbicide based on bio-availability, respectively. Therefore, these herbicides may damage the following corn crop in rotation although, corn was more tolerant to metsulfuron methyl sulfosulfuron. On the other hand, the persistence of bromoxynil MCPA and tribenuron methyl clodinafop propargyl herbicides in the soil was negligible and damage seems unlikely by theses herbicide in rotation.

Winter wild oat is an important and troublesome weed in wheat fields. Herbicides that inhibit the enzyme acetyl-coenzyme A carboxylase (ACCase inhibitors) have been widely used to control grass weeds such as wild oat in Iran, which has resulted in evolution of resistance to theses herbicides in wild oat. Whole-plant dose-response assay with 10 doses (from 0 to 32 times of the recommended rate, 64 g ai ha-1) was conducted to determine resistance level (RI) to clodinafop-propargyl (EC 8%) in 15 resistants and one susceptible wild oat populations from Fars and Khuzestan in southwest Iran. To evaluate the mechanism of resistance in resistant populations, cleaved amplified polymorphic sequence (CAPS) and derived cleaved amplified polymorphic sequence (dCAPS markers were used). The results of dose-response experiment clearly revealed that four (M2, M3, S4 from Fars and R5 from Khuzestan) out of fifteen populations were highly resistant to clodinafop-propargyl, where these populations were not even controlled over the range of 32 times of clodinafop-propargyl recommended rate. Therefore, resistance level in above population was greater than 21/93, the highest estimated RI for AN13. Three populations (M1, S1 and F3 from Fars) showed moderate resistance to clodinafop-propargyl with RI, 5-10. Based on molecular approaches, two known mutations (Ile-1781-Leu and Ile-2041-Asp) were identified in resistant populations. Results of a robust molecular assay demonstrated that the Ile-2041-Asp substitution occurred in M2 and R5 populations and the Ile-1781-Leu substitution occurred in the R5 population and 6 other populations; S1 S2, S3, S4, ES1 from Fars and AN13 from Khuzestan. This is the first report of a winter wild oat population carrying the both mutations in the world. Interestingly, this study revealed that Ile-2041-Asp substitution is associated with conferral of high-level resistance to clodinafop-propargyl and possibly other herbicides from FOPs family in winter wild oat.

In order to determine how exposure affects the Kautsky curve and its parameters, two dose-response experiments were carried out for chlorophyll fluorescence measuring.The treatments involved desmedipham phenmedipham ethofumesate, chloridazon and clopyralid on redroot pigweed (Amaranthusretroflexus L.)andblack nightshade (Solanum nigrum L.) at the research glasshouse of Agricultural Faculty of Ferdowsi University of Mashhad, Iran, during 2013. On the base of observation evaluation results, Solanum nigrum showed the highest susceptibility to desmedipham phenmedipham ethofumesate, so that application of 308.25 g a.i. ha-1 of herbicide resulted in 100 percent control, 21 days after treatment. The results of chlorophyll fluorescence showed that the mentioned herbicides effect was more in S. nigrum than in A.retroflexus.As Kautsky curve were affected and changed in an almost horizontal lines by desmedipham phenmedipham ethofumesate in both weed species at 4 HAS at doses of 51.38 mg a.i. ha-1,whereasthefluorescence rate was reduced in S. nigrum and A.retroflexusat doses of 81.25 and 325 mg a.i. ha-1 respectively bychloridazon. According to visual observations, chloridazon had significant effect on the control of Solanum nigrum and Amaranthus retroflexus, and clopyralid controlled Solanum nigrum better than Amaranthus retroflexus. Thefluorescence rate was decreased at doses of 240 mg a.i. ha-1 inA. retroflexus, 180 and 240 mg a.i. ha-1 for S. nigrum, and therefore, Kautsky curve was changed entirely. Among fluorescence parameters, Fvj andArea parameters were severely reduced.

Ientification and survey of weed distribution in fields and gardens is a main step for the management of these unwanted plants. The objective of the present investigation was identification and assessment of community indices,similarity, and distribution of weed species in the botanical garden of the University of Tabriz. In order to achieve this purpose, data sampling from weed species was performed by grid method (5 m × 5 m) in 13 sections of the botanical garden. Totally, 52 weed species from 25 plant families were recorded in different sections of the garden. Poaceae and Asteraceae with family dominance indices of 131/1 and 54/19, respectively, were the dominant plant families. Wall barley (Hordeum murinum) and cheatgrass (Bromus tectorum) with dominant indices of 73/38 and 35/11, were the first and the second dominant grass weeds. Burdock (Arctium lappa) and Persian speedwell (Veronica persica) with dominant indices of 44/61 and 23/97, were the first and the second dominant Dicot weeds. Maximum and minimum species diversity with Shannon-Wiener indices of 2.41 and 0.61 were observed in sections 13 and 7, respectively. Maximum and minimum richness were found in sections 2 and 5, respectively. The highest amount of Simpson dominance index in section 1 (14.78), indicates dominance of some weed species and reduction in uniformity of species distribution and species diversity in this section. Dodder (Cuscuta monogyna), as an important shoot parasitic weed, with relative dominance index of 3.55 out of 400, was one of the invasive weed species present in this garden. Presence of this parasitic weed in only one section of 13 surveyed sections, is an alarm for other sections.

In order to study the effect of rimsulfuron application time and dose on weed control and potato tuber yield, a field experiment was carried out in Ardabil during 2014. Treatments included different rates of rimsulfuron (0, 5, 10, 20, 30, 40 and 50 g ai ha-1), and rimsulfuron application time at different potato growing stages (potato emergence, stolon initiation and potato tuber bulking). A weed free treatment was also considered as control for evaluating potato yield components. Results showed that application of 50 g ai ha-1 rimsulfuron reduced weed biomass by 94.6 %. Which was not statistically different from 30 and 40 g ai ha-1. Among rimsulfuron application times, potato emergence produced maximum percent reduction of weed biomass. On the other hand, application of 50 g ai ha-1 at potato emergence stage caused the highest mean weight of potato tuber, tuber per plant and total tuber yield. There was no significant difference between 20, 30 and 40 g ai ha-1. Visual assessment results showed that rimsulfuron had minimum harm in potatoes which was negligible.

To investigate chemical control of dodder (Cuscuta campestrisYunk.) which is spreading insugarbeet fields, an experiment was conducted using metolachlor (commercial name Dual gold) at 1, 2, 2.5 &3 Lha-1, two formulations of propizamid (Wettable Powder: WP), commercial name Kerb and Suspension Concentrate: SC), commercial name Burst) at 1, 1.5, 2 &2.5 L/kg ha-1 and ethofumesate (commercial name Etho) 1, 1.5, 2 & 2.5 Lha-1. The experiment was performed in the Weed Research Department greenhouse, Karaj and Orumieh fields. The expermints were carried out in a randomized complete blocks design with 17 treatments and 4 replications in the greenhouse and 16 treatments with 4 replications in the fields. All dosages were sprayed at 4 leaf stages of sugarbeet and before dodder attatchment. The effect of herbicide treatments was analysed on dodder fresh and dry weight and sugarbeet yield. Greenhouse results indicated that propizamid Burst 2.5 Lha-1 as the the best herbicide treatment and caused the most decrease in dodder fresh and dry weight (93 to 99%, compared to dodder infested control), and also the most increase in sugarbeet shoot fresh and dry weight (51 to 94%) with Rasool cultivar. Based on field studies, propizamid Burst 2 to 2.5 Lha-1 and ethofumesate 2.5 Lha-1 were the best treatments. As SC formulation is safer and easier to apply than WP formulation, propizamid Burst 2 to 2.5 Lha-1 and ethofumesate 2.5 Lha-1 are recommended for dodder control in sugarbeet.

In order to study the effect of cover crops and sowing time on weed population and corn yield in minimum an conventional tillage systems, an experiment was conducted in the Seed and Plant Improvement Research Institute, Karaj, using Vicia villosa (V), Trifolium resupinatum (T) and Secale cereale (S) as cover crops, plus control (no cover crops, allowing weeds to grow). The cover crops were planted at three different dates of September 23rd, October 7th and October 27thin a corn field. In the first year (2013-2014) early ripening corn (Var. 108) was planted under minimum tillage. In the second year (2014-2015) late ripening corn (Var. 704) was planted under conventional tillage. Results indicated that the first cover plant sowing time was favorable in both years. This was mostly due to nitrogen availability of the soil which resulted in higher grain yield and better weed growth. Under minimum tillage, S reduced weed biomass by 34%. Under conventional tillage system, all the cover crops reduced weed biomass by 53%. Generally, percentage of organic carbon was higher in minimum tillage than in conventional system. S showed highest nitrogen uptake among the three cover crops in both tillage systems. In minimum tillage, the highest corn yield was under S cover crop with 5.304 t/ha. In conventional tillage, the highest corn yield was under T cover crop with 9.298 t/ha.

This study was conducted as intercropping of garlic and peas to assess the diversity, bio-mass, and population of weeds in two regions of Gonbad Kavoos and Sari during autumn 2013. The experiment was implemented in a randomized complete blocks design with three replications in both regions. Different combinations of intercropping were considered in nine levels of garlic and peas pure cultures, replacement intercropping of 75:25, 50:50, 25:75%, and additive intercropping of 100, 100, 100, 100흍 for garlic and peas. Results showed that the average biomass value of weeds in Sari (2080.5 gm-2) was greater than in Gonbad region. However, a higher weed density (44.88 m-2) was observed in Gonbad. The highest levels of biomass (3387.3 gm-2) and density (61.83 m-2) of weeds were measured for garlic pure culture in Sari and the intercropping replacement of 75% peas:25% garlic in Gonbad Kavoos. Mean value of Margalef species richness index, Menhinick index, and Shannon-Wiener diversity index were calculated as 1.33, 1.01, and 1.96 in Sari, respectively, which were higher than 0.86, 0.7, and 1.03 in Gonbad. By contrast, the Simpson's dominance index (0.63) for peas pure culture and Shannon-Wiener evenness index (0.89) to replacement intercropping of 75% peas: 25% garlic were greater in Gonbad Kavoos. Berger-Prager diversity index (0.77) for pure garlic culture, and both Shannon diversity (1.42) and Simpson's diversity (3.94) indices for replacement intercropping of 75% peas: 25% garlic were greater in Sari. There was a difference between the two regions in terms of climatic and edaphic characteristics which resulted differences in weed diversity indices, intercropping increased diversity while reducing dominance as compared to the monoculture cropping system in both regions.