-Two field experiments were conducted to evaluate the effects of multispecies weed competition on wheat grain yield and to determine their economic threshold on the crop. The experiments were conducted in 2002, on two sites in Iran: at the Agricultural Research Station on Ferdowsi University of Mashhad (E1) and on the fields of Shirvan's Agricultural College (E2). A 15 x 50 m area of a 15 ha wheat field in E1 and a 15 x 50 m area of a 28 ha wheat field in E2 were selected as experimental sites. These areas were managed like other parts of the fields, except for the use of herbicides. At the beginning of the shooting stage, 30 points were randomly selected by dropping a 50 x 50 cm square marker on each site. The weeds present in E1 were: Avena ludoviciana, Chenopodium album, Solanum nigrum, Stellaria holostea, Convolvulus spp., Fumaria spp., Sonchus spp., and Polygonum aviculare. In E2 the weeds were A. ludoviciana, Erysimum sp., P. aviculare, Rapistrum rugosum, C. album, Salsola kali, and Sonchus sp. The data obtained within the sampled squares were submitted to regression equations and weeds densities were calculated in terms of TCL (Total Competitive Load). The regression analysis model indicated that only A. ludoviciana, Convolvulus spp. and C. album, in E1; and A. ludoviciana, S. kali, and R. rugosum, in E2 had a significant effect on the wheat yield reduction. Weed economic thresholds were 5.23 TCL in E1 and 6.16 TCL in E2; which were equivalent to 5 plants m -2 of A. ludoviciana or 12 plants m -2 of Convolvulus spp. or 19 plants m -2 of C. album in E1; and 6 plants m -2 A. ludoviciana, 13 plants m -2 S. kali and 27 plants m -2 R. rugosum in E2. Simulations of economic weed thresholds using several wheat grain prices and weed control costs allowed a better comparison of the experiments, suggesting that a more competitive crop at location E1 than at E2 was the cause of a lower weed competitive ability at the first location.Keywords: weed interference, competition, grain yield, mathematical regression.RESUMO -Foram realizados dois experimentos para avaliar os efeitos da interferência de várias espécies daninhas sobre a produtividade e rendimento de trigo e determinar o seu nível de dano econômico (NDE) sobre a cultura. Os experimentos foram conduzidos em 2002, em dois locais no Irã: na Estação de Pesquisa Agrícola (EPA) da Universidade Ferdowsi, Mashhad (E1) e na EPA do Agricultural College, Shirvan (E2). Numa lavoura de trigo de 15 e 28 ha, nas Epa localizadas em E1 e E2, respectivamente, selecionaram-se áreas de 15 x 50 m como local dos experimentos. Estas áreas foram manejadas como outras partes do campo, exceto para o uso de herbicidas. No início do estádio de espigamento foram sorteados 30 pontos de coleta de 50 x 50 cm em cada local. As plantas daninhas presentes em E1 foram: Avena ludoviciana, Chenopodium album, Solanum nigrum, Stellaria holostea, Convolvulus spp., Fumaria spp., Sonchus spp., e Polygonum aviculare. No local E2 as espécies infestantes foram: A. ludoviciana, Erysimum sp., P. av...
Seed predation can be exploited as a mean of natural weed control. Field experiments were conducted in 2007 in four barely fields in Mashhad, NE of Iran to determine the effects of seed covering tissues, seed distribution patterns and interactions between seed density and background seed density on postdispersal seed predation. Five weed species (Avena ludoviciana,Hordeum spontaneum, Sinapis arvensis,Rumex obtusifoliusandRapistrum rugosum), three seed densities (50, 100 and 150 seed dish-1), two background seed densities (with and without), three distribution patterns (random, even, and aggregate), and two level of seed covering tissues (with and without) were arrange in a factorial randomized complete block design. Seed covering tissues had significant negative effect on predation and the most its effect was observed forH. spontaneum. Seed predation was also affected by seed distribution patterns. The highest and lowest seed predations of all species were observed from aggregate and random treatments respectively. The interaction between density and background seed density affected seed predation. Results show that seed predation can play an important role in decreasing the weed seeds on the soil surface and thus, in soil seed bank. Therefore, seed predation could be considered as a control technique in integrated weed management.
Temperature is a key factor for the living organisms on earth. It influences weed management practices, either directly or indirectly. Field experiments were conducted to determine the effect of temperature on the postdispersal seed predation of four important weed species (Cuscuta compestris, Stellaria media, Taraxacum officinale and Veronica persica) in two lucerne fields in Mashhad and Chenaran, north-eastern Iran. These two cities have the same climate: temperate and cold alpine but the temperature varies between them. Wire mesh cages were used to determine the relative importance of birds in predation and pitfall traps were used to detect the species and the activity density of invertebrate predators. The results showed that the predation preference of different weed species was significantly different between and within fields. Seed predation fluctuated widely throughout the sampling periods, matching the periodic forage harvest and regrowth cycle of lucerne. Despite the level of seed predation fluctuating, it declined toward the last sampling periods. Using wire mesh exclusion cages showed no significant effect of birds on weed seed predation in both fields. Ants, crickets and carabid beetles were the invertebrate seed predators that were caught in the pitfall traps. There were significant correlations between the mean temperature and predator activity densities and also between the predated seeds and the mean air temperature in both locations. The results of this study indicate the significant effect of temperature on postdispersal weed seed predation. Therefore, with respect to climate change and increasing global warming, it would be possible to focus on postdispersal seed predation in weed management in the future. Temperature infl uences seed predation25 Mean percentage of seed removal Weed species 4 S. Noroozi et al. Temperature infl uences seed predationTemperature influences seed predation 5
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