The critical period for weed control in dry-seeded rice

The critical crop-weed competition period in a dry-seeded rice system is an important consideration in formulating weed management strategies. Field experiments were conducted in the summer seasons of 2012 and 2013 at the Punjab Agricultural University, Ludhiana, India, to determine the extent of yield loss in two different rice cultivars (PR 114 and PR 115) with different periods of weed interference. Twelve weed control timings were used to identify critical periods of weed competition in dry-seeded rice. PR 114, a long-duration rice cultivar (145 d) having slower initial growth than PR 115 (125 d), was more prone to yield losses. In both years, 100% yield loss was observed where weeds were not controlled throughout the season. In weed-free plots, the grain yield of PR 114 was 6.39-6.80 t ha-1, for PR 115, it was 6.49-6.87 t ha-1. Gompertz and logistic equations fitted to yield data in response to increasing periods of weed control and weed interference showed that, PR 114 had longer critical periods than PR 115. Critical weed-free periods to achieve 95% of weed-free yield for PR 114 was longer than for PR 115 by 31 days in 2012 and 26 days in 2013. Weed infestation also influenced the duration of critical periods. Higher weed pressure in 2012 than in 2013 increased the duration of the critical period of crop-weed competition in that year. The identification of critical crop-weed competition periods for different cultivars will facilitate improved decision-making regarding the timing of weed control and the adoption of cultivars having high weed-suppressing abilities. This will also contribute to the development of integrated weed management in dry-seeded rice systems.

Weed dynamics as influenced by tillage system, sowing time and weed competition duration in dry-seeded rice

Cultural practices alter patterns of crop growth and can modify dynamics of weed-crop competition, and hence need to be investigated to evolve sustainable weed management in dry-seeded rice (DSR). Studies on weed dynamics in DSR sown at different times under two tillage systems were conducted at the Agronomic Research Farm, University of Agriculture, Faisalabad, Pakistan. A commonly grown fine rice cultivar 'Super Basmati' was sown on 15th June and 7th July of 2010 and 2011 under zero-till (ZT) and conventional tillage (CONT) and it was subjected to different durations of weed competition [10, 20, 30, 40, and 50 days after sowing (DAS) and season-long competition]. Weed-free plots were maintained under each tillage system and sowing time for comparison. Grassy weeds were higher under ZT while CONT had higher relative proportion of broad-leaved weeds in terms of density and biomass. Density of sedges was higher by 175% in the crop sown on the 7th July than on the 15th June. Delaying sowing time of DSR from mid June to the first week of July reduced weed density by 69 and 43% but their biomass remained unaffected. Tillage systems had no effect on total weed biomass. Plots subjected to season-long weed competition had mostly grasses while broad-leaved weeds were not observed at harvest. In the second year of study, dominance of grassy weeds was increased under both tillage systems and sowing times. Significantly less biomass (48%) of grassy weeds was observed under CONT than ZT in 2010; however, during 2011, this effect was non-significant. Trianthema portulacastrum and Dactyloctenium aegyptium were the dominant broad-leaved and grassy weeds, respectively. Cyperus rotundus was the dominant sedge weed, especially in the crop sown on the 7th July. Relative yield loss (RYL) ranged from 3 to 13% and 7 to16% when weeds were allowed to compete only for 20 DAS. Under season-long weed competition, RYL ranged from 68 to 77% in 2010 and 74 to80% in 2011. The sowing time of 15th June was effective in minimizing weed proliferation and rectifying yield penalty associated with the 7th July sowing. The results suggest that DSR in Pakistan should preferably be sown on 15th June under CONT systems and weeds must be controlled before 20 DAS to avoid yield losses. Successful adoption of DSR at growers' fields in Pakistan will depend on whether growers can control weeds and prevent shifts in weed population from intractable weeds to more difficult-to-control weeds as a consequence of DSR adoption.

Using simulation models to investigate the cumulative effects of sowing rate, sowing date and cultivar choice on weed competition

With the increasing pressure on crop production from the evolution of herbicide resistance, farmers are increasingly adopting Integrated Weed Management (IWM) strategies to augment their weed control. These include measures to increase the competitiveness of the crop canopy such as increased sowing rate and the use of more competitive cultivars. While there are data on the relative impact of these non-chemical weed control methods assessed in isolation, there is uncertainty about their combined contribution, which may be hindering their adoption. In this article, the INTERCOM simulation model of crop / weed competition was used to examine the combined impact of crop density, sowing date and cultivar choice on the outcomes of competition between wheat (Triticum aestivum) and Alopecurus myosuroides. Alopecurus myosuroides is a problematic weed of cereal crops in North-Western Europe and the primary target for IWM in the UK because it has evolved resistance to a range of herbicides. The model was parameterised for two cultivars with contrasting competitive ability, and simulations run across 10 years at different crop densities and two sowing dates. The results suggest that sowing date, sowing density and cultivar choice largely work in a complementary fashion, allowing enhanced competitive ability against weeds when used in combination. However, the relative benefit of choosing a more competitive cultivar decreases at later sowing dates and higher crop densities. Modelling approaches could be further employed to examine the effectiveness of IWM, reducing the need for more expensive and cumbersome long-term in situ experimentation.

Períodos de matocompetição na cultura da soja (Glycine max (L.) Merril), cultivares Santa Rosa e IAC-2: II - Efeitos sobre características morfológicas das plantas e constituição química dos grãos

Foram, conduzidos experimentos de campo com os cultivares Santa Rosa e IAC-2 em dois tipos de solos, Latossol Roxo e Latossol Vermelho Escuro - fase arenosa, no Município, de Jaboticabal (SP), com o objetivo de estudar a influência do período de competição das plantas daninhas sobre algumas características morfológicas relacionadas à produção e composição química dos grãos, na cultura da soja. O delineamento experimental utilizado foi o de blocos ao acaso, sendo os cultivares mantidos sem e com matocompetição por períodos cujas extensões foram 0, 10, 20, 30, 40, 50 e 60 dias após a emergência. Com base nos resultados obtidos, pode-se chegar à conclusão que um período inicial curto (20 a 30 dias) livre da matocompetição, foi suficiente para que não ocorressem efeitos negativos, estatisticamente significativos, na altura final das plantas, no diâmetro do caule e na altura de inserção da vagem mais baixa, além de ser suficiente para que os teores de proteína, extrato-etéreo e cinzas, dos grãos, se mantivessem dentro dos valores normais esperados para os dois cultivares, nos solos estudados.

Períodos de matocompetição na cultura da soja (Glycine max (L.) Merril), cultivares Santa Rosa e IAC-2. I- efeitos sobre os parâmetros de produção

Visando estudar a influência do período de competição das plantas daninhas sobre alguns parâmetros de produção da cultura da soja, foram instalados experimentos de campo com os cultivares Santa Rosa e IAC-2 em dois tipos de solos, Latossol Roxo e Latossol Vermelho Escuro - fase arenosa, no município de Jaboticabal, Estado de São Paulo, Brasil. O delineamento experimental utilizado foi o de blocos ao acaso , sendo os cultivares mantidos sem e com competição das plantas daninhas por períodos cujas extensões foram 0, 10, 20, 30, 40, 50 e 60 dias após a emergência. Com base nos resultados obtidos, pode-se concluir que: o período mínimo do início do ciclo que deve ser mantido livre de competição é de 30 a 40 dias após a emergência para o cultivar Santa Rosa e de 50 dias para o 'IAC-2'; para os dois cultivares, a produção de grãos foi efetivamente aumentada após o 20.° dia sem competição no solo Latossol Roxo e 30.° dia no solo Latossol Vermelho Escuro - fase arenosa, atingindo um valor máximo no 50.° dia para o 'Santa Rosa' e ao redor do 60.° dia para o 'IAC-2'; no ano agrícola de 1977/78 (solo Latosso l Roxo), a competição durante os primeiros 20 dias após a emergência causou perdas de produção em ambos os cultivares, entretanto, no de 1978/79 (solo Latossol Vermelho Escuro - fase arenosa) este período foi de 40 dias, mostrando a importância das interferências e da foclimáticas e das diferentes espécies daninhas, no processo de competição; e, dentre todos os parâmetros relacionados à produção de grãos, o número de vagens por planta foi o mais afetado pela competição das plantas daninhas.

The interrelationships of winter wheat cultivars, crop density and competition of naturally occurring weed flora

The effects of intraspecific and interspecific competition on a wide range of winter wheat cultivars were investigated in two consecutive split plot field experiments. Significant reductions of grain yield at greatly reduced seed rates were observed in the first experiment, whereas increasing crop density up to 380 plants m(-2) in the second experiment failed to produce a significant yield response due to compensation through increased ears and grains per plant at lower crop densities. Appreciable weed suppression and acceptable grain yield can be achieved at crop densities between 150 and 270 plants m(-2). Reductions in final yield due to weed competition occurred in both experiments; 11.7 and 13.6% for the first and second experiment, respectively, with the onset of weed competition occurring from tittering in the first experiment and from stem elongation in the second. The possibility of enhancing crop competitiveness for weed suppression and improved grain yield is discussed.

The interrelationships of winter wheat cultivars, crop density and competition of naturally occurring weed flora

The effects of intraspecific and interspecific competition on a wide range of winter wheat cultivars were investigated in two consecutive split plot field experiments. Significant reductions of grain yield at greatly reduced seed rates were observed in the first experiment, whereas increasing crop density up to 380 plants m(-2) in the second experiment failed to produce a significant yield response due to compensation through increased ears and grains per plant at lower crop densities. Appreciable weed suppression and acceptable grain yield can be achieved at crop densities between 150 and 270 plants m(-2). Reductions in final yield due to weed competition occurred in both experiments; 11.7 and 13.6% for the first and second experiment, respectively, with the onset of weed competition occurring from tittering in the first experiment and from stem elongation in the second. The possibility of enhancing crop competitiveness for weed suppression and improved grain yield is discussed.

Competition of sorghum cultivars and densities with Japanese millet (Echinochloa esculenta).

Field studies were conducted at two locations in southern Queensland, Australia during the 2003-2004 and 2004-2005 growing seasons to determine the differential competitiveness of sorghum (Sorghum bicolor L. Moench) cultivars and crop densities against weeds and the sorghum yield loss due to weeds. Weed competition was investigated by growing sorghum in the presence or absence of a model grass weed, Japanese millet (Echinochloa esculenta). The correlation analyses showed that the early growth traits (height, shoot biomass, and daily growth rate of the shoot biomass) of sorghum adversely affected the height, biomass, and seed production of millet, as measured at maturity. "MR Goldrush" and "Bonus MR" were the most competitive cultivars, resulting in reduced weed biomass, weed density, and weed seed production. The density of sorghum also had a significant effect on the crop's ability to compete with millet. When compared to the density of 4.5 plants per m2, sorghum that was planted at 7.5 plants per m2 suppressed the density, biomass, and seed production of millet by 22%, 27% and 38%, respectively. Millet caused a significant yield loss in comparison with the weed-free plots. The combined weed-suppressive effects of the competitive cultivars, such as MR Goldrush, and high crop densities minimized the yield losses from the weeds. These results indicate that sorghum competition against grass weeds can be improved by choosing competitive cultivars and by using a high crop density of > 7.5 plants per m2. These non-chemical options should be included in an integrated weed management program for better weed management, particularly where the control options are limited by the evolution of herbicide resistance.

Effects of weed control and fertilization at early establishment on tree nitrogen and water use in an exotic F1 hybrid pine of subtropical Australia

Purpose We investigated the effects of weed control and fertilization at early establishment on foliar stable carbon (δ13C) and nitrogen (N) isotope (δ15N) compositions, foliar N concentration, tree growth and biomass, relative weed cover and other physiological traits in a 2-year old F1 hybrid (Pinus elliottii var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Barr. ex Golf.)) plantation grown on a yellow earth in southeast Queensland of subtropical Australia. Materials and methods Treatments included routine weed control, luxury weed control, intermediate weed control, mechanical weed control, nil weed control, and routine and luxury fertilization in a randomised complete block design. Initial soil nutrition and soil fertility parameters included (hot water extractable organic carbon (C) and total nitrogen (N), total C and N, C/N ratio, labile N pools (nitrate (NO3 −) and ammonium (NH4 +)), extractable potassium (K+)), soil δ15N and δ13C. Relative weed cover, foliar N concentrations, tree growth rate and physiological parameters including photosynthesis, stomatal conductance, photosynthetic nitrogen use efficiency, foliar δ15N and foliar δ13C were also measured at early establishment. Results and discussion Foliar N concentration at 1.25 years was significantly different amongst the weed control treatments and was negatively correlated to the relative weed cover at 1.1 years. Foliar N concentration was also positively correlated to foliar δ15N and foliar δ13C, tree height, height growth rates and tree biomass. Foliar δ15N was negatively correlated to the relative weed cover at 0.8 and 1.1 years. The physiological measurements indicated that luxury fertilization and increasing weed competition on these soils decreased leaf xylem pressure potential (Ψxpp) when compared to the other treatments. Conclusions These results indicate how increasing N resources and weed competition have implications for tree N and water use at establishment in F1 hybrid plantations of southeast Queensland, Australia. These results suggest the desirability of weed control, in the inter-planting row, in the first year to maximise site N and water resources available for seedling growth. It also showed the need to avoid over-fertilisation, which interfered with the balance between available N and water on these soils.

Competition of sicklepod, cassia obtusifolia l., densities on soybean, glycine max (l.) merr., at variable row distance

Competition studies with soybeans, Glycine max (L.) Merr. "Bragg." and sicklepod, Cassia obtusifolia L., were conducted at the Agricultural Research and Education Center of the University of Florida in Quincy, Florida. Two field experiments were established, one on May 22, 1975. and the other four weeks later, on June 19, 1975, to determine the competitive effects of various sicklepod densities and the influences of soybean row distances on weed dry matter, soybear plant characteristics, yield components and seed yield, and on soil nutrient content. Control, low, medium, and high sicklepod densities in the first experiment were O, 25,000, 53,000, and 77,000 p1ants/ha, respectively; while the second experiment presented control, low, medium, and high sicklepod densities of O, 36,000, 68,000, and 122,000 plants/ha, respectively. Three soybean row distance treatments were tested using a constant pattern of 90-, 60-, and 45-cm widths throughout the growing season. Three other treatments, evaluated in a variable patern, were initially seeded in 30-cm row widths. Five weeks after planting, an appropriate number of soybean rows were harvested from the 30"cm pattern to establish row distances of 90, 60, and 30-60 cm for the remainder of the season. ln the greenhouse a test was conducted to evaluate the effects af those variables on seed germination and seedling vigor for the next soybean generation. As a result of full-season sicklepod competition, soybean plants were less branched, set fewer leaves, and presented thinner stems as compared to the control. However, height of soybean plants was not affected by the presence of sicklepod. ln one of the two experiments, number of nodes decreased for soybeans under weed campetition. The yield components--number of pods; number of seeds, and seed yield per soybean plant--were all similarly reduced due to weed competition. Seeds per pod were decreased to a lesser extent. Soybean seed yields per unit area were significantly diminished by increasing levels af sicklepod ínfestation. While the control produced 3120 kg/ha, the sicklepod densities of 25,000, 53,000, and 77,000 plants/ha reduced seed yíelds 47, 65, and 73%, respectively. As soybean row distances decreased, number of branches, number of leaves, and stem diameter of soybeans decreased. However, the height of soybean plants increased with narrwing of row width. The components of seed yield--number of pods, number of seeds, and seed yield per soybean plant--diminished as row spacing was reduced. Maximum difference between row distances for these attributes was attained for soybean plants under weed-free conditions. Generally, as row width decreased, soybean seed yield per unit area increased. Specifically, soybear.s in 90-cm rows, either in constant or variable row pattern, yielded less than soybeans in 60- and 30-60-cm rows in the variable pattern. Soil contents of phosphorus, potassium, calcium, and magnesium were not affected by the various levels of sicklepod and soybean populalions. Neither the sicklepod densities nor the soybean row distances influenced seed germination and seedling vigor in the next soybean generation. Sicklepod was a strong competitor with soybeans at all density ranges investigated. Because sicklepod grows taller than soybeans during the reproductive stages of the crop, limited success can be reached by varying row spacing alone. However, this practice is considered an integral measure to complement other methods of sicklepod control. Compared to constant rows, the soybean cropping system using variable row spacings presents the choice of planting soybeans at close row spacings to provide early competition with weeds and the possibility of obtaining a forage crop after the first month of growth, without any decreases on the final seed yields.

Períodos de interferência das plantas daninhas na cultura do algodoeiro (Gossypium hirsutum)

Com o objetivo de determinar os efeitos de períodos de controle e de convivência das plantas daninhas na produtividade da cultura do algodoeiro (Gossypium hirsutum), cultivar Delta-Opal, realizou-se um experimento que constou de dois grupos de tratamentos. No primeiro, a cultura permaneceu livre da competição das plantas daninhas desde a emergência até 7, 14, 21, 28, 35, 42, 49, 56, 63 dias e colheita (159 dias). No segundo, a cultura permaneceu em competição com a comunidade infestante desde a emergência até os mesmos períodos descritos para a primeira série de tratamentos. Dentre as espécies de plantas daninhas encontradas na área experimental, destacaram-se a tiririca (Cyperus rotundus), o fedegoso (Senna obtusifolia), a anileira (Indigofera hirsuta) e o capim-carrapicho (Cenchrus echinatus). Pelas condições edáficas, climáticas e florísticas sob as quais foi conduzida a cultura de algodão, o Período Anterior à Interferência (PAI) dessa comunidade que reduziu em 5% a produtividade da cultura foi de oito dias após a emergência da cultura (DAE); o Período Total de Prevenção da Interferência (PTPI) foi de 66 DAE; e o Período Crítico de Prevenção da Interferência (PCPI) foi dos 8 aos 66 DAE.

Weed control strip influences the initial growth of Eucalyptus grandis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Períodos de interferência das plantas daninhas na cultura da cana-de-açúcar: I - Tiririca

Com o objetivo de estudar períodos de interferência entre plantas daninhas e a cultura da cana-de-açúcar, foi instalado um experimento no município paulista de Pradópolis, numa área pertencente à usina São Martinho, onde a cana-deaçúcar foi plantada no mês de abril de 1995 e colhida quinze meses depois. As condições climáticas no estado de São Paulo após o plantio deste experimento (época normal de plantio da cana-de-açúcar no estado de São Paulo) são caracterizadas por deficiência hídrica e temperaturas amenas, sendo que o períodos chuvoso iniciou-se apenas quatro meses após o plantio. O resultados obtidos no experimento permitiram concluir que a cana-de-açúcar suportou um pequeno período de convivência inicial, de zero aos 41 dias após o plantio (DAP), sem sofrer interferência significativa de diminuição da produção. No entanto, o controle da tiririca por um período curto (dos aos 22 dias após o plantio da cana-de-açúcar foi suficiente para assegurar a produção.