فصلنامه مطالعات حفاظت گیاهان
سال سی و هشتم شماره 3 (پاییز 1403)

Lepidopteran pests are among the most important limiting factors for corn production (grain and fodder corn), which is one of the most important strategic products in the world and in Iran. In recent years, due to climate changes around the world, some secondary pests have become widespread. One of these pests is the false armyworm Mythimna loreyi. In Iran, until the past years, false armyworm did not cause significant damage. However, in recent years, its population has increased, and as a result, its damage is evident in the corn fields.

In the present research, the population of M. loreyi and the larval natural parasitism were assessed during three growing seasons (2021-2023). A one-hectare grain corn field was selected on the research farm of the Research Institute of Plant Breeding and Seed Preparation in Karaj, where no spraying was done during the season. In each weekly sampling, the number of M. loreyi larvae and the number of the parasitized larvae were recorded. Parasitized larvae were also transferred to the laboratory and the parasitoids were identified. At the end of season, 30 plants were infested with the target pest and 30 intact plants were sampled and the cobs weight was recorded for both groups. The percentage of cobs, which were infected with fungi after feeding the pest was recorded. To compare the temperature changes in the three evaluated years, the meteorological data for the sampling months were obtained. The SAS software was used for statistical analysis and mean comparisons.

The analysis of pest frequency data showed that frequency of the pest population increased, especially in the third year of the survey (2023). Population of the pest larvae showed a significant increase compared to the previous two years. Comparison of the average number of larvae in the first and second years based on the t test did not show a statistically significant difference (t value = 2.05; P = 0.06). However, it had a significant increase in the third year compared to the first year (t value = 4.34; P<0.01) and the second year (t value=2.63; P=0.019). The proportion of larvae population increased by 2.44 and 5.97 times, respectively, in the years 2022 and 2023 compared to 2021. Increase in the ratio of larvae population in 2023 compared to 2022 was also calculated to be 2.44 times. Comparing the average weight of the infected cobs that were fed by M. loreyi larvae with the control cobs showed a significant decrease in the weight of corn cobs due to the pest feeding (t value=3.94; p<0.01). On average, fungal contamination was observed in 75% of the cobs that were fed by the pest. Comparing the cumulative pest density data with the data related to temperature changes showed a possible relationship between larval density and the temperature. Comparison of the minimum temperature for four months (the months of pest activity on corn) in three years has shown that it was higher on June, August and September in 2023 than the corresponding months in 2021 and 2022. Therefore, considering density of the pest larvae and comparing three years, it seems that the minimum temperature had a role in increasing the pest density rather than the maximum and average temperature. Considering that based on the results reported by Qin et al. (2017) on the population of M. loreyi in China, this pest can grow at temperatures between 18 and 30 ̊C, the very high maximum temperature (such as the temperature experienced in August 2021 in Karaj and the mean maximum temperature reached above 37 ̊C) was not favorable for the pest and did not lead to its optimal growth. In the study of Mediouni Ben Jemâa et al., (2023) also a negative correlation has been reported between the number of captured adult M. loreyi and increasing temperature. Recently, M. loreyi has become one of the most important pests of cereals in Asia and Africa (Qin et al., 2017; Mediouni Ben Jemâa et al., 2023). It is possible that the increase in temperature in recent years in Iran has also provided optimal conditions for the appearance of M. loreyi, and results of the present study support this hypothesis. In this study, the average percentage of larval parasitism for three years was calculated between 11.74 and 14.86 percent. According to a study on M. loreyi parasitoids in Turkey, C. ruficrus was the most common parasitoid of this pest, and it was present in 91% of the fields where M. loreyi was active (Sertkaya and Bayram 2005). In the study of Sertkaya and Bayram (2005), the parasitism rate of C. ruficrus on M. loreyi was 38.5%, which was about 2 times more than compared to the highest average percentage of parasitism in the present study (14.86% at 2023). However, this average is related to the entire sampling period, and in all three years in the first half of September, the percentage of parasitism was recorded above 60% (Table 1). Therefore, this parasitoid has a high potential to control the population level of M. loreyi and the results of Sertkaya and Bayram (2005) confirm this claim based on the natural efficiency of C. ruficrus against M. loreyi by 42.4%.

The damage of M. loreyi is higher in late-season corn or corn that is cultivated later. In Iran, fodder corn is often sown as a second crop after harvesting wheat and barley. Considering the water crisis in the country on the one hand, and the importance of fodder corn in feeding livestock and providing fodder in the country on the other hand, which is very closely related to the country's food security, investigation on different aspects of M. loreyi biology, damage and management is necessary, before this pest emerges as an important and main pest in the country.

 Vinca minor or lesser periwinkle is a perennial, herbaceous and creeping plant belonging to the genus Vinca and the family Apocynaceae. In addition to being an ornamental and cover plant, V. minor is a valuable herbal plant in traditional medicine, and it also acts as a natural source for the industrial manufacture of brain blood flow stimulants. Periwinkle contains more than 150  alkaloids, which have been isolated from the aerial parts and roots of the plant, so far (Proksa et al.,1988), consisting of vincaminorine, vincaminoreine, minovine, minovincine, vincamine, which has antihypoxic and neuroprotective properties as well as modulatory effects on brain circulation and neuronal homeostasis (Farahanikia et al., 2011). Vinca mosaic virus (VMV), belonging to the genus Potyvirus and the family Potyviridae, causes severe to mild mosaic symptoms, yellowing, blistering and leaf curl in the leaves of the periwinkle plant. In this study, the molecular and phylogenetic characteristics of two isolates of VMV were investigated via analysis of p1 and cp genes.

 Virus-like symptoms, such as mosaic and mottling, yellowing, blistering and leaf curling were found on the leaves of V. minor plants in the pardis campus of Ferdowsi University of Mashhad, Razavi Khorasan, Iran, during a survey in September 2019. Total RNA was extracted from the leaves with the SV Total RNA Isolation Kit to determine the causal agent(s) (Promega, USA). Deep sequencing was carried out on the samples by Macrogen Company in South Korea. Analysis of the results with CLC Genomics Workbench v.12.0.3 software showed that these plants were infected with two isolates of VMV. The cp and p1 gene sequences of VMV isolates were determined. Clustal Omega software was used to compare multiple sequence alignments among sequences and determine the percentage of identities at the nucleotide and amino acid levels. To determine phylogenetic relationships and evolutionary origin of Iranian VMV isolates, phylogenetic tree was drawn based on nucleotide and amino acid sequences of cp and p1 genes using MEGA 7 software and Maximum-Likelihood (ML) method with 1000 replications (Bootstrap). The SDT software (v.1.2) and Muscle sequencing were used to plot the similarity matrix among the isolates at the nucleotide and amino acid levels.

 The identities between the cp gene of two Iranian VMV isolates (VMV-IR-1 and VMV-IR-2) at the nucleotide (nt) and amino acid (aa) levels were 93.11% and 97.00% respectively. For the p1 gene, the obtained results showed 68.35% identity at the nt level and 97.00% at the aa level. The highest percent of nt identity of the VMV cp with other potyviruses in the GenBank was with ASV1 (asparagus virus 1) (75.00% with VMV-IR-1 and 73.82% with VMV-IR-2) VMV-IR-1 and VMV-IR-2 showed the highest aa identity with VDMV (vanilla distortion mosaic virus) (70.39%). The highest nt and aa identity of p1 gene of VMV isolates was with CatMV (catharanthus mosaic virus) (52.29% VMV-IR-1 and 51.31% with VMV-IR-2) and ZTMV (zucchini tigre mosaic virus) (28.70%), respectively. Protected motifs were also identified in the cp and p1 gene sequences. Dendrograms obtained from phylogenetic analysis based on nt and aa acid sequences of these genes placed two Iranian VMV isolates, along with other species of potyviruses in the GenBank, viruses in two and three separate groups respectively. Based on cp gene sequences, at the aa level Iranian VMV isolates is most closely related to yam mosaic virus (YMV) virus, and at the nt level with the closest viruses are include sweet potato virus 2 (SPV2), sugarcane mosaic virus (SCMV), onion yellow dwarf virus (OYDV) and johnsongrass mosaic virus (JGMV) in the same group. Based on the p1 gene sequences, VMV isolates at the nt level were most closely related to the JGMV virus and at the aa level were most closely related to the YMV and celery mosaic virus (CeMV) viruses.

 In this study, for the first time, the molecular properties of VMV isolates were determined based on the cp and p1 genes, and the phylogenetic position of two Iranian VMV isolates was drown. The results showed that the cp gene can be used for taxonomic purposes. Considering the medicinal and ornamental properties of periwinkle and effect of the viruses on its properties, special attention should be paid to viral diseases of this plant.

Introduction:

Esca of grapevine (Vitis vinifera) is an important complex disease in almost all areas, where grapevines are grown. The symptoms of this disease may affect the trunk, branches, shoots (brown wood-streaking and white rot of trunk), leaves (light green or chlorotic, irregular areas between the veins or along the leaf margin, which gradually spread from the basal to the distal parts of the shoot) and fruit (tiny brown spots and sometimes wilt of berries). Toxins are secondary metabolites, which are important virulence factors of phytopathogenic fungi. Phaeoacremonium aleophilum (Pal), Phaeomoniella chlamydospora (Pch), and Fomitiporia mediterranea (Fme) produced two pentaketides (scytalone and isosclerone), and the α-glucan named pullulan. Several evidences indicated that at least some of these metabolites may induce the characteristic symptoms of diseases. The main objective of this research was to establish a clear efficient and cheap method using callus and extracted toxic metabolites in order to select susceptible, tolerant, or resistant commercial grapevine cultivars to the esca disease.

Esca-associated fungi were obtained from the Agricultural Research, Education and Extension Organization (AREEO), Khorasan Razavi province, Iran. Five mL of a suspension of three mentioned fungi (10-day-old) in 50 ml sterile water were added to 1 L flask containing 150 mL Czapek Dox medium amended with 0.1% yeast and 0.1% malt extract. They were incubated at 25°C for 28 days in the dark. The mycelia were removed by filtration using Filter membranes, nitrocellulose 0.22 μm. The toxic secondary metabolites were extracted from this suspension. Briefly, the culture filtrates from each fungus (2 L per strain) were treated with equal volumes of cold ethanol-acetone and incubated in an ice batch for 4 to 6 hours. The resulting precipitates were extracted by centrifugation at 3000 rpm for 10 seconds. Recrystallization was done by dissolving the polymer in hot water and adding the same volume of ethanol to it, and the formed precipitate was filtered through a Whatman filter, dried at 40°C and weighed. The toxic metabolite obtained from liquid cultures of each fungal species was assayed on detached leaves of 5 grapevine commercial cultivars of Khorasan Razavi province, including Torkaman8(TU8), Kolahdari(KOL), Torkaman6(TU6), Fakhri Shahrood(FSH), and Keshmeshi-Quchan(KQU). The leaves with their petioles were immersed in a 3 mL solution until complete absorption, which usually took a few hours, and then were transferred to distilled water. Callus of the five grapevine cultivars, micro propagated shoot cultures were cultivated on modified MS media containing 15, 30, and 45% toxic metabolites. The grown callus was inoculated with different concentrations of toxic metabolites,  then dry weight of callus and vital cells were measured visually, as well as spectrophotometrically, by using Triphenyl Tetrazolium Chloride (TTC).

Results and Discussion:

The Pal, Pch, and Fme fungi were all able to produce toxic secondary metabolites, but an isolate of the Pal fungus obtained from Memlejeh (a village in the Central District of Bojnord County, North Khorasan Province, Iran.) produced a large amount of pullulan. The symptoms produced on the detached leaves that absorbed a toxic solution were quite similar to those observed on the leaves of the same cultivars naturally infected by the same fungal species. Differences between cultivars in symptom severity were also observed under experimental conditions. The results showed that reduction of the callus dry weight in TU8 grapevine cultivar was the lowest (26%) compared to the other cultivars tested, followed by KOL (31%) and TU6 (40%) cultivars. The KQU and FSH cultivars showed the highest reduction in callus dry weight (48% and 44%, respectively). The effect of pullulan produced by three important esca-associated fungi indicated that the toxin produced by the Fme fungus had the least effect and the Pal fungus showed the greatest effect in reducing dry weight of the callus. Dry weight of the callus in 15% concentration of the toxic metabolite showed the least decrease and maximum decrease of the callus weight was obtained in 45% concentration. Among the cultivars tested, the callus cells of Torkaman 8 had the highest optical density, which means the number of living cells was more than other cultivars. The KQU cultivar with minimal live callus cells showed more sensitivity to the metabolite. Toxin of the Fme fungus had the least and that of the Pal fungus had the most effect on the callus cells. The percentage of survival rate in the inoculated callus cells of Torkaman 8 compared to the KQU cultivar at 45% concentration of the extract was about 50.36% and the survival rate in the KQU cultivar was about 15.51%. Also, the obtained results showed that the grapevine cultivar TU8 was comparatively more tolerant than other cultivars tested. On the other hand, the FSH and KQU cultivars were susceptible to secondary metabolite of the mentioned fungi.

Occurrence of the esca diseases is increasing in grapevine all over the world, whereas efficient therapeutic strategies are lacking. The use of toxic metabolites of esca-associated fungi and tissue culture of the host plants under in vitro conditions could be cheap,easy, and helpful assays for controlling the disease via selection, improvement, and reproduction of the tolerant genotypes. According to the reaction of grapevine cultivars to the secondary metaboilte of esca-associated fungi, it can be concluded that the TU8 grapevine cultivar is less sensitive than the KQU grapevine cultivar against the esca disease.

 Weeds and diseases significantly hinder agricultural production. Chemical pesticides are frequently used to control weeds and plant diseases in many fields. However, they have numerous adverse effects. Therefore, it is advisable to consider using natural pesticides, which have fewer environmental impacts and decompose more rapidly, to try to protect plants. Currently, there is a growing recognition of the potential of plant extracts as a useful resource for the development of natural herbicides and fungicides. Saffron (Crocus sativus L.) is cultivated as one of the important medicinal plants in Iran. Saffron leaves and corm can be used as natural pesticides as available and cheap sources. Saffron extracts have been found to possess antiherbal and antifungal properties by multiple sources.

 In order to evaluate the antiherbal and antifungal properties of saffron leaf and corm extracts on the germination and growth characteristics of whitetop weed and Aspergillus niger fungus, independent factorial experiments were conducted based on the completely randomized design with four replications at the Faculty of Agriculture of Birjand University in 2022. The allelopathic treatments consisted of two saffron organs (leaf and stem) and seven extract concentrations (0, 0.25, 0.5, 1, 1.5, 2, and 4% v/w). The antifungal treatments consisted of two saffron organs (leaf and corm) and seven extract concentrations (0, 0.0312, 0.625, 0.125, 0.25, 0.5, and 1 by v/w). Whitetop seeds were collected from the research field of the Faculty of Agriculture of Birjand University in 2022. Saffron leaves and seeds were harvested from four-year-old plantations in Sarayan city, then subjected to drying and grinding. To create the aqueous extract, a mixture of 40 g of dehydrated saffron leaves and corms was combined with 1000 ml of distilled water. The mixture was then placed on a shaker at a speed of 200 revolutions per minute for a duration of two hours, resulting in the preparation of the stock extract. Subsequently, the extract was diluted with double distilled water to prepare the necessary concentrations for the experiment. To examine the fungicidal properties of saffron extracts, the Potato Dextrose Agar (PDA) culture media were used containing different concentrations of the extract. After solidification of the culture media, 5 mm diameter mycelial plug of the fungus was inserted upside down in the middle of each Petri plate using a cork borer. Subsequently, the petri dishes were sealed with parafilm and relocated to the incubator set at 25ºC temperature. They were maintained under these specific circumstances until the completion of each test period.

 Results Results of the experiments showed that the type of extract was significant only on the mean germination time of whitetop and the highest mean germination time (MGT) was obtained from the corm extract. The corm extract showed the maximum germination time. Regarding the impact of concentration on seedling, it was discovered that concentrations up to 0.5% had a stimulatory effect, while higher concentrations had an inhibitory effect on the attributes of whitetop plants. Increasing the concentration of the extract to 4% resulted in reduction of 21.9%, 17%, and 22% in the root length, root fresh weight, and shoot fresh weight, respectively. The findings of this experiment indicated that 4% concentration of the corm extract resulted in the lowest shoot dry weight and seedling dry weight. The lowest dry weight of root was obtained using 2% concentration of the corm extract. The antifungal test findings indicated that Aspergillus niger fungus exhibited the smallest colony diameter on the third day when treated with 0.0312%, 0.625%, and 1%. concentrations of the leaf extract. Any antifungal effect was not observed in the media treated with the extract compared to the controls. The experimental findings revealed that saffron extracts, when present in high quantities, effectively suppressed the growth of whitetop weed. However, the concentrations of saffron extracts used in this study were insufficient to avoid the growth of A. niger. The study demonstrated the allelopathic effects of saffron leaf and corm extracts on various plant species including Amaranthus retroflexus (Rashed Mohassel et al., 2009), Rapistrum rugosum (Alimoradi et al., 2008), Plantago psyllium (Rashed Mohassel et al., 2009), Gypsophylla pilosa (Azizi et al., 2013), Hordeum spontaneum (Ghesmati et al., 2018), Agropayron repense (Ghesmati et al., 2018), and Cardaria draba (Soltanipoor et al., 2006). Furthermore, the saffron extracts were found to have antifungal properties against Fusarium oxysporum (Rubio-Moraga et al., 2013), Aspergillus parasiticus (Tzanidi et al., 2012), Candida albicans (Vahidi et al., 2002), Penicillium raistriicki (Rubio-Moraga et al., 2013), and Bipolaris spicifera (Rubio-Moraga et al., 2013) in previous studies. Hence, extracts derived from saffron leaves and corms possess antiherbal and antifungal properties 

 Overall, the findings of this study indicated that saffron extract type did not have any impact on the seedling traits of whitetop weed. Nevertheless, saffron extract with concentration of less than 0.5% exhibited a stimulating impact, whereas at higher concentrations had an inhibitory influence on the characteristics of whitetop. The used amounts of saffron extracts failed to inhibit the growth of A. niger. Hence, based on the findings of this experiment, it is advisable to examine effect of higher doses of saffron extracts on A. niger.

Powdery mildews belong to the order Erysiphales, class Leotiomycetes, and phylum Ascomycota. These fungi belong to the family Erysiphaceae and cause a fungal disease called powdery mildew in various host plants. The symptoms of powdery mildew are mostly seen as spots or a layer of white, yellow, brown, or gray mycelium (conidiophores) or spherical sexual structures with yellow, brown to black color (chasmothecium). As obligate biotrophs, powdery mildew fungi obtain their nutrients from living cells of their host plants through specialized feeding organs known as the haustoria. The host range of this group of fungi is limited to Angiosperms, and no powdery mildew is known to occur on gymnosperms. The life cycle of most members of the Erysiphaceae family consists of both sexual and asexual stages, and only in a few genera, the asexual stage is not known. The infection usually starts rapidly with conidia on the leaf surface. The conidia of powdery mildew fungi are transferred by wind from infected hosts to other plants and to initiate infection, they germinate on the budding leaves of plants and form appressorium, leading to the formation of haustorium. With more than 7500 plant species and a diverse climate, Iran harbors many plant pathogenic fungal species, including powdery mildew causing fungi. According to the available literature, about 33 species belonging to nine genera, which cause powdery mildew, have been identified and described from Ardabil province. As we know, the major use of land in Ardabil province is for agriculture and pasture. For this reason, fungi belonging to the Erysiphaceae family are important and diverse in this province. Due to limited studies in this area, the fungi causing powdery mildew disease on various plants in some cities of Ardabil province including Ardabil, Parsabad, Khalkhal, Sarein, Meshginshahr, Namin and Nir were investigated and identified in the present study.

To study powdery mildew fungi, samples of various crops, landscapes, fruit trees, and forests were collected from some cities of Ardabil province during the years 2021 and 2022. Each sample was given a unique code corresponding to the host. The plant samples were identified with helping of a botanist and using literature related to the flora of Iran. Microscopic slides were prepared from different structures of fungi such as sexual and asexual forms. Morphological characteristics of the samples were measured and recorded to identify the fungus causing the disease via microscopic analyses using an optical microscope. In the case of fresh fungal samples, conidia germination was investigated according to the method described by Cook and Braun (2009). Finally, powdery mildew species were identified using Braun and Cook's (2012) monograph and related literature at the level of genus and species. In addition, microscopic color photos were prepared with helping of a digital camera connected to a Zeiss optical microscope.

In recent years in Iran and compared to other important groups of fungi, articles related to fungi have been significant and are increasing more or less. Some recent publications include lists of powdery mildew causing fungi from Iran, but they are often incomplete and limited to regional studies (Khodaparast et al., 2002; Tavanaei et al., 2005; Pirnia et al., 2007). In the past, according to the research conducted in Ardabil province, until today, about 32 species belonging to 9 genera powdery mildew causing fungi have been identified and described (Davari et al., 2015). In this research, seven genera and 33 species including Erysiphe (13 species), Golovinomyces (4 species), Leveillula (3 species), Neoerysiphe (1 species), Phyllactinia (2 species), Podosphaera (9 species) and Sawadaea (one species) were identified from the Erysiphaceae. Erysiphe trifoliorum on clover (Trifolium tumens), Golovinomyces orontii specie complex on ash (Fraxinus excelsior) and lettuc (Lactuca scarioloides),G. sonchicola on prickly sow-thistle (Sonchus asper) and L. taurica on common vetch (Vicia sativa) are reported for the first time from these new hosts from Iran. Also, 11 species on 14 hosts, including E. capreae, E. prunastri, E. trifoliorum, E. ulmi var. ulmi, G. cichoracearum, G. orontii, L. chrozophorae, L. taurica, P. euphorbiae, P. fusca and P. plantaginis are reported for the first time, on these hosts from Ardabil province.

Among the fungal species causing powdery mildew in Ardabil province, four species are reported for the first time from Iran on related host plants, including Golovinomyces (two species), Erysiphe (one species), and Leveillula (One species). Moreover, 11 species are reported for the first time from Ardabil province including Erysiphe (four species), Podosphaera (three species), Golovinomyces (two species), and Leveillula (two species). Generally, Erysiphe and Podosphaera genera with 13 and nine species were the most prevalent genera, respectively. Powdery mildew causes a decrease in yield and product quality as a result of direct and indirect damage; hence, accurate identification of these fungi, their host range, and geographical distribution can be useful in biodiversity studies as well as management of these pathogens.

Oilseeds are very important as the raw material for the production of vegetable oil (one of the basic needs of the society in the food field). Therefore, achieving any success in increasing the amount of production and supplying as many of these products as possible to meet the domestic needs of the country is considered a valuable and great success. Safflower, with the scientific name Carthamus tinctorius L., is an annual long-day plant from the chicory family. Wild mustard (Sinapis arvensis L.), which is also called Brassica kaber in some literatures, is one of the most important weeds belonging to the Brassicaceae family. Competition can perhaps be considered the most important biological interference factor effective in determining crops productivity.Effective management of weeds in agricultural systems is very decisive. Extensive and repeated use of herbicides has led to the emergence of resistant weed biotypes, which has often increased the cost of control. It has also caused some concerns about the negative environmental effects of herbicides. When the competition is for light, the competitive ability of the species is first determined by the morphological traits. The response of crop height to weed competition is related to the density and intensity of competition and the type of weeds and can be positive or negative.

An split plots experiment based on randomized complete block design with three replication was carried out in the Research Farm of University of Birjand during the 2018-2019 cropping year. The treatments include four level of phosphorus fertilizer (0, 25, 50 and 75 kg P 2O5 ha-1) as the main plot and the four wild mustard densities (0, 7, 14 and 28 pl m-2) as subplots. Plant growth characteristics were measured from 150 to 210 days after planting (DAP) in five stages at 15-day intervals. Also, at the harvest maturity, the yield and yield components of the crop were determined.

According to the results, the highest (35.48 g m-2) and lowest (28.23 g m-2) safflower leaf dry weights were obtained from control (no-mustard) and 28 pl m-2 mustard densities at 165 DAP, respectively. The highest (1.67) and lowest (1.19) leaf area index of safflower were achieved at 210 DAP using 25 and 50 kg P 2O5 ha-1, respectively. Based on these results, it can be concluded that the most effective level of phosphorus on the improvement of safflower growth traits (e.g. leaf area and dry weight and stem dry weight) and its competitive ability was 25 kg P2O5 ha-1, although the its effects were not significant for many traits, and as phosphorus levels increased, the competition shifted more in favor of wild mustard. In accordance with these results, and probably due to luxury consumption by weeds, it has been observed that when weed density is high, adding fertilizer leads to superiority of weed growth over crop (Blackshaw et al., 2008). Also, the highest leaf area index of mustard (0.63) was obtained at a density of 56 mustard pl m-2 at 165 DAP and the lowest one of (0.26) was observed at a density of 14 pl m-2 at the same time. It was also observed that the height and leaf area index of wild mustard were the highest in all measuring stages at higher weed densities, indicating the competitiveness of the weed. The increase in weed density had a negative impact on the safflower, although insignificant in many cases, which could be the result of the competitive effect of mustard for resources such as radiation and nutrients (Wright et al., 1999).

In general, the increase in weed density had a positive effect on the yield and its components in wild mustard and a negative effect on the safflower, and under these condition, the application of more than 25 kg P2O5 ha-1 does not have a positive effect on the crop. Thus, it seems that the revision in weed management and the use of fertilizer as an agronomic strategy can be effective in reducing the crop losses caused by the presence of high densities of weeds (Clements et al., 2014).

Continuous rice cultivation in the paddy fields of northern regions in Iran has led to the spread of weeds such as Echinochloa crus-galli and Paspalum distichum gradually. The presence of these grass weeds in paddy fields leads to waste of water and nutrients and adversely affects on rice productivity. Herbicide application helps for keeping the fields free of weeds during the critical period and minimize the costs of weeding and allows for selective weed control. No repeated application of herbicides or mixed application of herbicides are necessary, because these strategies need to prevent herbicide resistance in weeds. This experiment aimed to assess and compare the effectiveness of some herbicides, including metsulfuron-methyl, tiobencarb, bispyribac sodium, triafamon + ethoxysulfuron, cyhalofop-butyl, and the tank mixed application of cyhalofop-butyl and bispyribac sodium, in controlling grassy weeds in the rice fields.  

A field experiment was conducted in Gilan Agricultural and Natural Resources Research and Education Center (Rasht) in 2021, utilizing a Randomized Complete Block Design (RCBD) with three replications and 15 treatments, including tiobencarb 50%EC at 2750 and 3000 g a.i. ha-1, bispyribac sodium 40%SC at 26 g a.i. ha-1, triafamon+ethoxysulfuron 30%WG at 37.5 and 45 g a.i. ha-1, cyhalofop-butyl 20%OD at 100 g a.i. ha-1, bispyribac sodium 40%SC at 26 g a.i. ha-1 + cyhalofop-butyl 20%OD at 100 g a.i. ha-1, metsulfuron-methyl 60%DF at 6 and 8 g a.i. ha-1, pertilachlor 50%EC at 875 g a.i. ha-1, twice hand weeding, and weedy check. Thiobencarb, pertilachlor, and triafamon + ethoxysulfuron were applied in water, five days after transplanting, and cyhalofop-butyl, metsulfuron-methyl, and bispyribac sodium were applied to the weeds at the two- to four-leaves stage, using a knapsack sprayer equipped with a flat fan nozzle. Weed control via application of herbicides was evaluated visually based on the European Weed Research Society rating scale and weed density and biomass were assessed. The yield of rice from each plot was measured. The data collected for different parameters were subjected to analysis of variance (ANOVA) using R-studio and the treatment means were compared using Duncan's Multiple Range Test at a significance level of 1%.

All weed control treatments significantly increased the weed control efficiency (WCE) over the weedy check. Triafamon + ethoxysulfuron and tiobencarb in both examined doses had the highest WCE in reducing E. crus-galli pressure with 100% control. After that the effectiveness of pertilachlor at 875 g a.i. ha-1and cyhalofop-butyl at 100 g a.i. ha-1 in reducing E. crus-galli density was ≥90% and biomass reduction was ≥78%. There were no significant differences between these treatments in controlling E. crus-galli. The highest WCE in P. distichum control was observed in applying triafamon + ethoxysulfuron at doses of 37.5 and 45 g a.i. ha-1 with ≥91.1% and ≥94.4% density reduction and ≥95.6% and ≥99.8% biomass reduction, respectively; followed by application of cyhalofop-butyl with ≥83.6% and ≥79.7%, density and biomass reduction, respectively. After that, tiobencarb in both doses resulted in ≥72% density reduction and ≥84.5% biomass reduction. There was no significant difference between these treatments in P. distichum control. Pertilachlor was not very effective in controlling of P. distichum; its efficacy was 48.8, 56.5, and 78.4% biomass reduction, in three samplings, respectively. The highest efficacy of metsulfuron-methyl in controlling E. crus-galli and P. distichum was 75.9 and 73.1%, respectively for biomass reduction in the first sampling in the application of 8 g a.i. ha-1. Herbicide application resulted in improved rice grain yield compared to the weedy check. The highest grain yield of rice was achieved with tiobencarb at doses of 3000 and 2750 g a.i. ha-1, yielding 5051 and 4965 Kg ha-1, respectively. There was no significant difference between observed manually weeded treatment and thiobencarb treatments, and also with bispyribac sodium, pertilachlor, triafamon + ethoxysulfuron in both doses (45 and 37.5 g a.i. ha-1), and cyhalofop-butyl; these treatments increased grain yield by 68.4, 65.5, 54.56, 52.8, 39.2, 35.4, 34.6%, respectively, compared to the weedy check. 

The results of this research showed that application of triafamon + ethoxysulfuron at 37.5 g a.i. ha-1 or thiobencarb at 2750 g a.i. ha-1 applied at 3-5 days after rice seedlings transplanting into the water, or application of cyhalofop-butyl at 100 g a.i. ha-1 in the form of a foliar spray in the stage of two- to four-leaf of grass weeds were the efficient control practice for both grass weeds (E. crus-galli and P. distichum) in paddy field.