Background Temperature plays a key role in plants distribution. Cardinal temperatures are important parameters for plant population dynamics models.Aims This study was conducted to estimate the cardinal temperatures and other parameters in relation to temperature using three non-linear regression models (segmented, dent-like and beta) to project the germination rate and temperature relation of Papaver dubium and P. rhoeas.Methods An optimisation method was used to fit the models and their statistical parameters. Their efficiency was compared with the coefficient of determination (R2), root mean square error (RMSE) and the Akaike Information Criterion.Results Calculated cardinal temperatures differed for different germination percentiles (10, 30, 50%). The time required to 50% germination of both P. dubium and P. rhoaes was more accurate than the time required to 10% and 30% germination between observed and predicted values. According to the outputs of the segmented model, base, optimum and maximum temperatures of P. rhoeas were 1.9°C, 22.4°C and 39.6°C, respectively. The corresponding values for P. dubium were 2.1°C, 22.1°C and 39.1°C.Conclusions The parameters related to temperature provide the basic information to determine the time needed for germination and to project potentially suitable areas for invasion. The segmented model is appropriate for the estimation of the cardinal temperatures of both Papaver species.
In Asia, Echinochloa glabrescens is one of the most common Echinochloa species in rice production systems. The use of weed-competitive rice (Oryza sativa L.) cultivars and rice density are important components of integrated weed management tools, but their use requires understanding the extent to which rice can interfere with E. glabrescens growth and how the weed may respond to this interference. Growth of E. glabrescens was studied in a screenhouse by growing it alone and with 4, 8, and 16 plants of two rice cultivars (Rc222 and Sabita). Sabita was taller than Rc222, but Rc222 had greater biomass than Sabita. E. glabrescens produced greater shoot biomass and seeds plant−1 when grown with Sabita than with Rc222. Increases in rice density progressively reduced the number of leaves, leaf area, shoot biomass, and seed production of E. glabrescens. However, E. glabrescens grown with the highest rice density responded with increased leaf weight ratio, leaf area ratio, and specific stem length. Despite such plasticity, E. glabrescens shoot biomass and seed production decreased by 83% and 88%, respectively, when grown with 16 rice plants (approximately 80 kg seed ha−1) compared with its biomass and seed production without crop interference. The results suggest that rice interference alone may significantly reduce the growth of E. glabrescens but may not provide complete control. This highlights the need to integrate different weed management strategies to achieve complete control of E. glabrescens and other weeds in direct-seeded rice systems.
Different herbicides are currently required for sustainable weed management in aerobic rice. Three pot experiments were conducted using different herbicides to evaluate rice safety and for the control of Echinochloa colona, a major weed of aerobic rice. Among the pre-emergence (PRE) herbicides, it was found that pendimethalin (594 g ai ha−1) and flumioxazin (60 g ai ha−1) were relatively safe herbicides for rice and provided 100% control of E. colona. All other PRE herbicides, such as atrazine, cinmethylin, clomazone, dimethenamid-P, isoxaflutole, metribuzin, prosulfocarb + S-metolachlor, pyroxasulfone, trifluralin, and S-metolachlor reduced the biomass of rice compared with the non-treated control. Dose-response studies revealed that flumioxazin and pendimethalin even at low doses (30 g ai ha−1 for flumioxazin and 294 g ai ha−1 for pendimethalin) provided excellent control (>95%) of E. colona. Post-emergence (POST) application of paraquat (360 g ai ha−1) at the time of rice emergence caused toxicity in the crop, but also provided excellent control of E. colona. When applied just after crop emergence (11 days after sowing), Pendimethalin was found to be safe for rice (2% mortality) and reduced the biomass of E. colona by 88% compared with the non-treated control. It is quite possible that the rice variety Reiziq used in this study may have a tolerance to flumioxazin, which needs further investigation involving more rice varieties. This study suggests that flumioxazin can be used as an alternative to pendimethalin for the sustainable management of E. colona in aerobic rice.
L. (Billy goat weed; Asteraceae) is an annual herbaceous plant of American origin with a pantropical distribution. The plant has unique biological attributes and a raft of miscellaneous chemical compounds that render it a pharmacologically important herb. Despite its high medicinal value, the constant spread of the weed is noticeable and alarming. In many countries, the weed has severely invaded the natural, urban, and agroecosystems, thus presenting management challenges to natural resource professionals and farmers. Its interference with agricultural crops, grassland forbs, forest ground flora, and its ability to replace native plant species are of serious concern. Therefore, it is pertinent to monitor its continuous spread, its entry into new geographic regions, the extent of its impact, and the associated evolutionary changes. While management strategies should be improvised to control its spread and reduce its adverse impacts, the possible utilization of this noxious weed for pharmacological and agronomic purposes should also be explored. The objective of this review is to provide a detailed account of the global distribution, biological activities, ecological and environmental impacts, and strategies for the management of the agro-environmental weed
The efficacy of metolachlor on rigid ryegrass was determined under a no-till seeding system in an experiment conducted in 2004 and 2005 in South Australia. Metolachlor at a rate of 0.48 and 0.96 kg ai/ha was applied at 40 or 46 d (very early preplant, VEPP) and 20 or 23 d before crop sowing (early preplant, EPP), and at sowing (preplant, PP) in 2004 and 2005; the herbicide was incorporated by sowing. The control of rigid ryegrass was greater than 80% when metolachlor was applied PP; however, that application resulted in phytotoxic effects on emergence and yield of wheat; metolachlor was more phytotoxic when applied at 0.96 kg/ha than at 0.48 kg/ha. Metolachlor applied EPP provided 71 to 83% rigid ryegrass control, whereas VEPP application provided only 33 to 49% control. Reduction in wheat grain yield was not observed at these application times. This study indicates that metolachlor at 0.48 kg/ha could be safely applied around 20 d before crop sowing to selectively control rigid ryegrass in wheat.
The present paper reviews current knowledge on how changes of plant metabolism under elevated CO2 concentrations (e[CO¬2]) can affect the development of the glyphosate resistance of C3 and C4 weeds. Among the chemical herbicides, glyphosate, which is a non-selective and post-emergence herbicide, is currently the most widely used herbicide in global agriculture. As a consequence, glyphosate resistant weeds, particularly in major field crops, are a widespread problem and are becoming a significant challenge to future global food production. Of particular interest here it is known that the biochemical processes involved in photosynthetic pathways of C3 and C4 plants are different, which may have relevance to their competitive development under changing environmental conditions. It has already been shown that plant anatomical, morphological and physiological changes under e[CO¬2] can be different, based on (i) the plant’s functional group, (ii) the available soil nutrients and (iii) the governing water status. In this respect, C3 species are likely to have a major developmental advantage under a CO¬2 rich atmosphere, by being able to capitalize on the overall stimulatory effect of e[CO¬2]. For example, many tropical weed grass species fix CO2 from the atmosphere via the C4 photosynthetic pathway, which is a complex anatomical and biochemical variant of the C3 pathway. Thus, based on our current knowledge of CO2 fixing, it would appear obvious that the development of a glyphosate-resistant mechanism would be easier under an e[CO¬2] in C3 weeds which have a simpler photosynthetic pathway, than for C4 weeds. However, notwithstanding this logical argument, a better understanding of the biochemical, genetic and molecular measures by which plants develop glyphosate resistance and how e[CO2] affects these measures will be important before attempting to innovate sustainable technology to manage the glyphosate-resistant evolution of weeds under e[CO2]. Such information will be of essential in managing weed control by herbicide use, and to thus ensure an increase in global food production in the event of increased atmospheric [CO2] levels.
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