مجله پژوهش علف های هرز
سال دهم شماره 1 (بهار و تابستان 1397)

This research project was conducted to study the population and biodiversity indices of weed species in wheat fields in Qazvin province/Iran during the 2015/2016 cropping season. A networking sampling method was employed to study the weed species in three wheat production systems of no-tillage-rainfed (low input), no-tillage-irrigated (intermediate input), and moldboard-tillage (high input)-irrigated systems. Sampling was conducted at two growing stages (Tillering and end of stemming). The species diversity of Simpson, Shannon-Weiner, Margalof richness, Menhinic and dominance index were determined by genus and species. The dominance index in dry farming fields (0.9245) was higher than irrigated farms, and in irrigated farms with moldboard tillage (0.7451) was higher than no-tillage irrigated fields (0.6664). The Shannon index in low input farms (2.9693) was more than high input (1.5230) treatment and in high input farms was more than intermediate input (1.4346) treatment. The highest Margalof richness index was obtained from dry farming system (1.8516) while the lowest was observed in no-till fields (0.7432). The species richness index in low input farms was more than high input and in high input was more than intermediate input (with conservative tillage) fields. The results of this project demonstrated that no-till production system is associated with less weed species and diversity in wheat fields.

The use of tolerant cultivars is one of the most important methods for parasitic weed managing. In order to screen of 19 Serbian tomato cultivars tolerance to Orobanche aegyptiaca under greenhouse conditions, an experiment was arranged as a factorial experiment, based on completely randomized design with three replications. The tolerance of these cultivars was investigated in the presence and absence of broomrape in separately treatments. The results showed that among the studied Serbian cultivars, express, uragan, donator, red stone and leader cultivars were more tolerant than other cultivars. Despite of high dry weight production in express cultivar, it suffered the least damage (44.75%) compared to other cultivars. The lowest broomrape dry weight was observed at uragan and donator cultivars. However, their aboveground biomass reduced to 35.39% and 58.16% respectively. Despite the higher biomass production in fantom, ox heart, honey and profit cultivars in control treatments, they suffered severe damage (more than 80%) in infected treatments. It seems theses cultivars are more susceptible to broomrape than the others.

In order to investigate the variation in cardinal temperature of wild mustard seed germination during the removal of dormancy, a split plot experiment based on a completely randomized design with three replications was conducted at Seed Research Laboratory of Gorgan University of Agricultural Sciences and Natural Resources in 2017. The main factor was different temperatures (5, 10, 15, 20, 25 and 30 °C) and different periods of chilling (0, 2, 4, 6 and 8 days at 5 °C) were assigned as the sub-factor. To describe the response of germination rate to temperature, a dent function was used. For different germination stages, the base temperature decreased from 2.9 to 3.4 °C in control seeds to 1.5 to 1.8 °C in 4 days chilling. Ceilings temperature in control seeds was 25 °C, which increased to 29.9 to 32.9 °C as a result of 6 chilling for 6 days. Due to cardinal temperature changes, the physiological dormancy of wild mustard is of type I. Dormant seeds originally have the highest germination at low temperatures, and they germinate at high temperatures after elimination of dormancy. Also, the germination temperature range increases. Estimated parameters in this study can be useful in seed bank simulation models and for further studies on wild mustard biology and ecology.

Changing tillage systems and plant residue application are regarded as suggested methods to improve weed management. A 3-year field experiment was conducted to evaluate the effects of soil tillage methods (conventional tillage (CT), reduced tillage (RT), and no-till (NT)) and wheat residue (residue preservation and removal) on weed growth and corn yield at Zarghan, Fars province. The experimental design was as split plot based on randomized complete block in three replications. Results showed that the lowest weed growth was obtained by CT method when wheat residue preserved while applying NT method enhanced perennial weed infestations. In other words, applying NT method increased perennial weed density up to 60% compared to CT and RT methods, but annual weed infestations decreased 40%. The kernel yield of corn (14447.64 kg ha-1) increased 34% when RT method accompanied by wheat residue compared to NT method. Applying CT method and residue preservation was maximized kernel number per cob (No. 576) and harvest index (36.82%) compared to RT and NT methods by four and 15%, respectively. It is concluded that, in consecutive corn cultivation, to grantee the corn yield potential and suppress weed growth applying RT method and preservation of 30% of wheat residue (standing residue with a height of 30 cm), is recommended.

More than twenty years after registration of tribenuron methyl herbicide in Iran, there are reports on its lack of efficacy in controlling broad leaved weeds in wheat fields of Ramiyan Township. To investigate the occurrence of resistance to tribenuron methyl in wild mustard (Sinapis arvensis L.), a series of experiments were conducted at Gorgan University of Agricultural Sciences and Natural Resources in 2016. Putatively resistant wild mustard biotypes were gathered from wheat fields of the Township. A susceptible biotype was also gathered from the fields with no history of spraying. Putative biotypes were first screened with the recommended dose. Then, response of susceptible and resistant biotypes to various doses of tribenuron methyl herbicide was investigated. The results of dose-response assay implied occurrence of resistant to tribenuron methyl in some wild mustard biotypes. Resistance factors of RAM-R-14, RAM-R-27, RAM-R-25, RAM-R-30 and RAM-R-5 were obtained respectively 3.90, 4.10, 3.96, 2.66 and 2.36. Distribution map of fields infested with susceptible and resistant wild mustard biotypes was drawn using geographic information system and it was revealed that the gathered biotypes were observed in the fields which possessed unsuitable cropping pattern and weed management was based on chemical control. The results of the present study may be utilized to implement herbicide-resistant weed management practices as well as prevention of development of these plants to other regions.

Purple nutsedge, is one of the most burdensome weeds in the agroecosystems, due to the rapid growth and proliferation of underneath tubers. The tubers are the main means of propagation and distribution of Purple nutsedge. Information on environmental conditions that regulate the growth of the vegetative organs would help to predict the emergence time of perennial weeds. Several methods of germination were tested to compare the germination potential and determine the thresholds (the main temperatures) for germination of the tubers. The results showed that the () and ( methods are not an appropriate index for estimating the temperature thresholds and evaluating sprouting potential. Based on germination rate (tubers per day -1) and weighted germination rate (tubers per day-1) indices, temperatures of 25 and 30°C were the best temperatures. On the other hand, based on the thermal germination rate index, (tuber per°C -1 per day-1) the best temperature is 25°C. Among indices, the thermal germination rate index is a more justified assessment for precise description of sprouting potential versus temperature due to take into account the amount of used heat. In order to study the germination percentage, germination rate, weighted germination rate, Dent-like model showed better fit (R2 adjusted =0.83 to 0.99) but for study of the thermal germination rate index segmented model was superior model (R2 adjusted =0.76). In general, the minimum, optimal and maximum range of germination of Purple nutsedg was determined to be between 7.51 to 9.20, 28.5 to 32.62, and 0.43 to 42.49 ° C, respectively.