Amaranthus blitoides S. Watson and A. hybridus L. are common herbaceous annual summer weeds in different regions of Iran, which produce a large number of small seeds per plant. The goal of these ...experiments was to determine seed germination cardinal temperature and investigate the effect of constant temperature, osmotic and salt stresses, stratification, flooding duration, after‐ripening and seed planting depth on seed germination and seedling emergence. Two‐piece segmented, dent‐like and beta four‐parameter models were used to investigate the relationship between germination rate and constant temperature. The dent‐like model showed the best description of the effect of constant temperature on seed germination rate of both A. blitoides and A. hybridus. Optimal seed germination of A. blitoides occurred at 35°C, but in A. hybridus optimum germination was observed in a range of constant temperatures from 30 to 40°C. Osmotic and salt stresses and flooding adversely affected seed germination of both species. After ripening for 6 months increased germination percentage of both A. blitoides and A. hybridus. Maximum seedling emergence of A. blitoides (42.8%) and A. hybridus (44.9%) occurred at a planting depth of 3.3 cm, whereas further increased planting depth minimized seedling emergence of both weeds. Information obtained from this study will help us to develop effective techniques for management of A. blitoides and A. hybridus.
Hand weeding is a common method of weed control on vegetable farms, especially in developing countries. It requires considerable physical labour and is a significant economic burden, yet comparative ...studies on hand weeding tools are rare. We evaluated the agronomic, ergonomic and economic performance of four hand weeding tools (and unweeded control) at two sites and two weed ages. Agronomic efficiency was evaluated based on the reduction in weed load from pre-weeding to post-weeding, economic efficiency based on the time taken to weed, and ergonomic efficiency based on heart rate and energy expenditure of the tool operator. Among the tools, the chipping hoe provided higher weed control efficiency than the rotating hoe and combined tool, and showed a lower average heart rate and workload than the combined tool. Ergonomic performance was superior in loam soil compared with clay. The light-weight chipping hoe provided better weed control than heavier tools while also reducing the workload of the weeder. Tools did not differ in economic performance, but the cost was 50% higher with late weeding. Viable hand weeding strategies require the optimization of tools for ergonomic performance and careful attention to timing of operations, thus benefiting economic performance.
Hyparrhenia hirta is a pasture grass that has become highly invasive in several parts of the world, including Australia where it has become a serious environmental weed in recent decades. Knowledge ...of the likely potential distribution and relative abundance of this invasive species, under current and future climate scenarios, will help biosecurity and weed control authorities to plan better strategies to manage the invasion. The CLIMEX modelling package was used to investigate the impacts of climate change on the potential global distribution of H. hirta, based on eco-physiological data. The worldwide potential distribution of H. hirta under current climatic conditions is vast and far greater than the current distribution, with suitable climate conditions extending over much of the tropics and subtropics. Under future climate scenarios, the range of H. hirta is likely to expand into areas currently too cold for its survival and contract from areas that are projected to become hotter and drier under climate change. The effects of likely climatic scenarios on the global potential distribution of H. hirta are sufficiently great that they should be considered routinely in strategic control plans for biotic invasions. Changes in the potential range of an invasive species such as H. hirta, under global warming scenarios, will mean that it could invade new jurisdictions. Knowledge of this emerging threat could help to formulate effective prevention, surveillance and response measures in these presently marginally unsuitable regions.
Summary
Plant eradication is difficult, particularly in remote, protected areas. The Southern Ocean Islands are very isolated and highly protected, but the flora contains many alien plants. Small ...restricted populations have been eradicated, but eradication of established species has proven difficult. A better understanding of the efficacy of control methods at sub‐Antarctic temperatures and their off‐target impacts may increase eradication success. With interest in controlling non‐native Poa annua in the region, we aimed to determine if physical and chemical methods can control P. annua (the sub‐Antarctic biotype) in sub‐Antarctic conditions and examined their impact on native plants. We quantified the effectiveness of physical control methods on P. annua in situ on sub‐Antarctic Macquarie Island through field‐based experiments and assessed their selectivity on P. annua compared with native grasses. We also quantified the effectiveness of several herbicides on P. annua at sub‐Antarctic temperatures and assessed their selectivity on native grasses. Of the four physical disturbance methods tested, none effectively reduced P. annua cover as one‐off treatments. Of the herbicide treatments, glyphosate and trifloxysulfuron sodium were effective and were less damaging to native grass species, indicating potential selectivity. Physical control was of limited effectiveness, but did not affect native species richness. An integrated weed management programme utilising the strategic use of selective herbicides with follow‐up chemical and physical intervention may balance control and biodiversity outcomes. This research highlights the importance of site‐specific testing of control methods and understanding off‐target impacts of control when managing alien plant species in protected areas.
Napier grass (Pennisetum purpureum Schumach.) is an important fodder and relatively drought-tolerant crop in tropical and subtropical regions, especially in developing countries. For this and other ...species, tools are needed for identifying drought-tolerant cultivars to aid selection for semi-arid environments. We determined tissue water status, carbon assimilation, biomass yield and forage quality for Napier grass cvv. Bana and Atherton grown in bins and subjected to three soil-water supply levels (100, 50 or 25% of field capacity) in glasshouses set at either low (15-25°C) or high (25-35°C) temperature regimes, over three growing cycles. Our aim was to explore whether differences in leaf water potential (LWP) and carbon assimilation rates could be reliable indicators of the relative yield potential and forage quality of the two cultivars in environments prone to water and heat stresses. At the low soil-water supply of 25% and low temperature, Bana had lower (more negative) LWP and relative water content (RWC) than Atherton, while at 50% and 100% soil-water supply, Bana had a higher tissue water status. Under the high temperature regime, Bana had consistently more positive LWP and RWC than Atherton, but the differences were not significant. The two cultivars had a similar CO2 assimilation rate (A) and there were no significant differences in the total dry matter yields over the three growing cycles. Water-use efficiency for above-ground biomass (kg ha-1 mm-1) was similar for both cultivars and was 28.5–35.1 under the low temperature regime and 16.9–22.9 under the high temperature regime. Neutral detergent fibre (NDF) was often higher for Bana at low water supply and low temperature than for Atherton, but the trend was reversed under the high temperature regime. Digestibility was generally improved under water-stressed conditions, and there was a positive correlation between NDF and both LWP and RWC measured at midday, but only under the low temperature regime. We conclude that LWP, RWC and A, alone or together, are inadequate for selecting cultivars for dry and hot environments, because cultivars may differ in other mechanistic responses to water stress and high temperatures.
Ten accessions of Napier grass (Pennisetum purpureum Schumach.) were evaluated for their dry matter (DM) yield and forage quality in a semi-arid lowland (Katumani) and a relatively wet highland ...(Muguga) over seven growth cycles from 2011 to 2013 in tropical Kenya. Three biomass yield clusters were identified from the 10 accessions as high-yielding (HYC), medium-yielding (MYC) and low-yielding (LYC) clusters for both sites. Total biomass (shoot and root) yields (t ha−1) over the seven growth cycles were 25.3 for HYC, 22.2 for MYC and 19.6 for LYC at Katumani and 40.0, 41.4 and 29.1 at Muguga. Total biomass yield averaged over the study period was DM 22.4 t ha−1 at Katumani and 36.8 at Muguga. Rainfall productivity was higher at Katumani (28.8 kg ha−1 mm−1) than 20.8 kg ha−1 mm−1 at Muguga. Neutral detergent fibre (NDF) was lower in LYC, which was more leafy than the other clusters and there was little difference in NDF between the two sites.
The physiological response of two species of grasses with C3 and C4 mechanisms syndromes, Napier grass (Pennisetum purpureum Schumach × Pennisetum glaucum (L.) R. Br) and hydric common reed grass ...(Phragmites australis (Cav.) Trin. Ex Steud) was examined under ambient (aCO2) and elevated CO2 (eCO2), in combination with water and temperature stress treatments. Under eCO2 and subjected to water and temperature stress, the Napier grass maintained higher daytime leaf water potential (LWP) by reducing transpiration (E) and executing larger osmotic adjustment (OA) at an average of 0.85 MPa compared with 0.42 MPa for common reed; carbon assimilation (PN) was thus higher for the Napier grass. Under aCO2 and low temperature, water stress induced no significant differences in OA between the grasses, but Napier grass still had higher PN than that of common reed. Recovery in LWP and PN following re-watering of water-stressed plants was more rapid in Napier grass than that in the common reed; the former had also higher water-use efficiency due to its low specific water use (water use/leaf area) that was just a fraction (less than 6%) that of the common reed. Exposure of common reed to eCO2 reduced stomata number, but increased it in the Napier grass, especially when subjected to water stress and high temperature. Exposure to eCO2 enhanced OA capacity and E control in Napier grass resulting in superior physiological profile over the common reed subjected to water and heat stress.
Chilean needle grass Nassella neesiana (Trin. & Rupr.) Barkworth; CNG is a perennial spear grass that has invaded pastures in south‐eastern Australia and can lead to a substantial reduction of ...stockcarrying capacity during the summer months. This study examined a range of grazing, herbicide and pasture resowing options, alone or in combination, on CNG and introduced pasture grass basal cover, for several CNG‐infested sites in south‐eastern Australia. At each site, options were chosen on the basis that they were most likely to control the CNG infestation while maintaining a productive sheep‐grazing enterprise on grass pastures. After 2 years of management, the reduction in CNG basal cover in set stock plots that were sprayed with flupropanate, versus those not sprayed, ranged from non‐detectable to a reduction of 80%, depending on site location. After 5 years of management, the reduction ranged from zero to 50%. Grazing management or sowing of competitive pastures did not generally reduce CNG basal cover to low levels. None of the management options maintained reasonable levels of desirable perennial species by the end of 4–5 years. We conclude that, because of the persistence of CNG, the need for regular spraying of herbicide, and the relative ineffectiveness of other control methods, management systems may need to be developed that utilize CNG while minimizing its input to the soil seedbank.
Isoxaflutole at 75 g ai ha⁻¹ is registered in Australia for the control of several broadleaf weeds in chickpea (Cicer arietinum L.). Although isoxaflutole provides satisfactory control of problematic ...weeds, under certain conditions crop injury can occur. Higher air temperature and moisture content of soil are reported to affect the metabolism of soil applied herbicide. Controlled environment experiments were used to determine the tolerance of chickpea to isoxaflutole under a range of temperature and soil moisture levels. For the soil moisture study, the variables examined were two desi chickpea genotypes (Kyabra as a tolerant cultivar and Yorker as a sensitive cultivar), three soil moisture levels 50 % field capacity (FC), 75 % FC and FC with three herbicide rates 0, 75 (recommended rate) and 300 g ai ha⁻¹. For the temperature by soil moisture study, the variables examined were two other desi chickpea genotypes (97039-1275 as a tolerant line and 91025-3021 as a sensitive line), three temperature regimes (20/5, 30/15 and 35/25 °C), two soil moisture conditions (50 % FC and FC) with the same three herbicide rates. The results demonstrated that the chickpea genotypes exhibited differential tolerance to isoxaflutole, but that differences in response were affected by rate, temperature and soil moisture. Increasing temperature and soil moisture content made the susceptible chickpea genotype more vulnerable to isoxaflutole damage. Injury to the susceptible genotype in terms of increased leaf chlorosis and reduction in shoot height and dry matter production increased as soil moisture increased from 50 % FC to FC and temperature increased from 20/5 to 35/25 °C. Overall damage of the sensitive genotype from increasing rates of isoxaflutole also increased when soil moisture content increased from 50 % FC to FC within the fixed temperature regime of 30/15 °C. The sensitivity of chickpea to isoxaflutole depends on existing temperature and moisture content and the chances of crop damage were enhanced with increasing temperature and moisture levels.
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