The suggestion that some woody weed species may be replaced by native plant succession in the absence of disturbance in New Zealand is not new (McQueen 1993; Williams 2011). However, this is the first study to systematically survey woody weed populations throughout New Zealand to determine which species regenerate under their own canopy, and which have predominantly native understories. Twenty-seven woody weed species had zero, or very few, conspecific seedlings or saplings beneath the parent canopy, and most had ≥ 50% cover of native species in the understory at one or more sites. Accordingly, these 27 species appear to have the most potential to be replaced by native succession in the absence of disturbance. Most of these 27 species are widely established throughout New Zealand (Howell & Terry 2016), so the management implications are significant. It should be noted, however, that the current study excluded sites where domestic livestock or dense populations of pest animals, exotic grasses or ground cover weeds were present; successional trajectories under these scenarios are uncertain. Additionally, data from a single site should be interpreted with caution; there may be considerable variation at different types of sites and/or under different conditions. For example, no Pseudotsuga menziesii seedlings were recorded at any of the five sites surveyed in the current study, but other authors have suggested that P. menziesii can invade New Zealand beech forest, particularly where the canopy and/or understory is relatively open (Ledgard 2002; Burmeister et al. 2016). Given increasing concerns over the invasive potential of P. menziesii in New Zealand (Froude 2011), further research into the shade tolerance of this species would be valuable.
Weed populations or biotypes expressing resistance to glyphosate and other herbicides have become more wide spread and in some cases more difficult to manage in agricultural systems. Determining genotypic and phenotypic variation among populations can increase knowledge that may be useful in developing weed management strategies. Assessment of genetic diversity among and within eight Palmer amaranth biotypes collected from North Carolina and Georgia using Amplified Fragment Length Polymorphism (AFLP) markers revealed levels of genetic diversity to be high, ranging in value from 0.0773-0.8605. Cluster and Principal Coordinate (PCO) analyses grouped individuals mostly by geographic origin irrespective of either resistance or susceptibility to glyphosate or gender of individuals. Analysis of Molecular Variance (AMOVA) results indicated that within biotype contribution towards total variation was always higher and significant (P < 0.0001) than among biotypes. Resistance in a Palmer amaranth biotype from North Carolina was found to be incompletely dominant, nuclear inherited, and might not be consistent with a single gene mechanism of inheritance.
269 Read more
Direct comparison of weed abundances in indi- vidual treatments after one year of SSWM provides better information about the effect of SSWM on the development of weed populations. For 2012, there is some tendency towards higher abundances of G. aparine and annual grasses observable in treatment 4. That is in contrast to the previous year, when treatment 4 showed the lowest in- festation with G. aparine and the abundance of annual grasses was about evenly balanced for all treatments. Nevertheless, the differences in abun- dances between treatments were not statistically significant (P = 0.270 and P = 0.608 for G. aparine and annual grasses, respectively). Other weed groups showed relatively balanced distribution among treatments in 2012, with no significant differences. ANOVA probability values for the null hypothesis on abundance differences among treatments for all important weed species are summarized in Table 3.
This work is focused on evaluating the effects of site-specific weed management (SSWM) on weed populations over a 4-year period. SSWM was used on a 3.07 ha experimental field during 2011–2014 in a rotation of winter wheat and winter oilseed rape. The area was split into application cells of 6 × 10 m and weed abundance was evaluated manually in each cell. Four different herbicide treatments were tested. Standard whole-field herbicide application (blanket spraying) was treatment 1. Treatments 2, 3 and 4 comprised SSWM using different thresholds for post- emergent herbicide applications. SSWM resulted in herbicide savings of 6.3–100% for Galium aparine, 0–84.4% for other dicotyledonous weeds, and 31.3–90.6% for annual monocotyledonous weeds. SSWM led to significantly increased density of G. aparine and Tripleurospermum inodorum in the final experimental year when compared to the blanket treatment. Negative correlation coefficients between 2011 and 2014 plant densities found in SSWM treatments (−0.237 to −0.401) indicate that Apera spica-venti does not establish a long-term soil seed bank.
Interactions between the major management factors and ecological responses to biotic factors, such as the degree of winter chilling available for dormancy breaking, or drought tolerance during the critical establishment phase, are responsible for much of the seasonal variability. As these interactions are difficult to observe, a modelling approach is needed to understand the complexity of the system and predict responses with sufficient detail to be of practical value across a range of scenarios. Several researchers have questioned the practicality of constructing predictive models to describe weed community changes. Freckleton and Stephens (2009) proposed that short-term detailed responses of absolute numbers at a local scale may be difficult to predict with accuracy, largely because of the seasonal variation we highlight in this study. However, they state that predictions of long- term shifts in response to broad-scale patterns of management may be possible, helping to devise sustainable management strategies. We suggest that while management approaches will predominantly affect the species traits needed for success under a particular regime, it is the biotic factors that will determine which species with these traits will dominate within a particular season.
34 Read more
North Carolina is the fifth largest producer of blueberries (Vaccinium spp.) in the U.S. with approximately 5,000 acres harvested in 2006. A study was conducted to determine if a positive correlation exists between the weed populations in field drainage ditches and weed populations in the field interior, and to inventory the weed species present in the ditches and the field interiors. Sixty-six species were inventoried over a two year period. A second study was conducted to define the seed biology of Rhexia mariana L., an aggressive perennial weed in blueberry, by determining temperature effects on germination, average seed number per capsule, seed number in the seed bank, and seed dormancy. Maximum seed germination was observed at day/night temperatures of 20/35C. Seed germination ranged from 47 to 86% and dormancy ranged from 14 to 53%. The number of seed capsules produced per infested area was different among locations and ranged from 500 to 1125 capsules/m 2 . Across locations, seed capsules produced an average of 74 seeds each. On average, 27 R. mariana seeds were present in each 273cm 2 sample of soil. A single m 2 of R. mariana infestation has the potential to produced 12,375 seed capsules and 915,750 seeds. Of those seeds, roughly 604,395 would be viable, 519,779 could germinate as freshly mature seeds, and an additional 84,615 seeds would be dormant. An estimated 1000 R. mariana seeds could germinate from 1m 2 of the soil seed bank. A third study was conducted to determine the efficacy of
96 Read more
The application maps for pinoxaden, clopyralid and metsulfuron-methyl + tribenuron-methyl are shown in Figure 2. All of the herbicide savings for the individual treatments are listed in Table 4. The results confirm the patchy distribution of weed populations in crop fields and show that, even if the mean weed infestation is relatively high, site-specific weed management can provide a good potential for herbicide savings. Wallinga et al. (1998) showed that actual herbicide saving is considerably affected by spatial resolution of the sprayer. In this research, a 6 × 10 m grid was used for weed sampling and herbicide application. Increasing the spatial resolution will probably result in a higher reduction of herbicide use.
The reservoir of weed seeds in the soil or on the soil surface is literally referred as weed seedbank and it determines the pattern of weed seed germination, species composition and potential densities of weeds that interfere with crops during next cropping season (Rahman et al., 1996). Annual weed populations are established every year because of persistent seed banks in arable soils. As most of the weed species in arable cropping systems are annuals, some knowledge of the seedbank may be a good starting point for an integrated weed management programme (Forcella 1993). Quantification of the weed density and diversity, pattern of weed seed germination and depth of weed seed viability in the 0-15 and 15-30 cm depth of soil is key to understand and devise suitable weed management plan. In order to exploit the potential of using the weed seed content, diversity and depth of seed viability in the soil could be useful to predict future weed problems and techniques to maintain weed population under economic threshold level. The present investigation was carried out to examine the distribution of arable weed seeds in surface and sub-surface areas of fodder cowpea field.
(e.g. Matricaria maritima subsp. inodora and Veronica arvensis) decreased rapidly a er exceeding a sowing depth of 0.01 m. Mutual relationships between size, shape, and seed germination are complex and speciﬁ c to each weed (Grundy et al., 2003). Regarding to the viability of weed seeds taken from the soil, it is radically shorter than that one of seeds le in the ground (Demo, 1999). Similarly, Sahoo (1998) found that weed seeds placed in the top layer of soil lost their viability in germination much faster than seeds placed into deeper soil. Swanton et al. (2000) discovered that the vertical distribution of the seed soil bank was aﬀ ected by the soil tillage system, ploughing depth, and the soil type (sandy soil). Caetano et al. (2001) conﬁ rmed that the qualitative and quantitative distribution of the weed seed soil supply is dependent on cultivation practices in speciﬁ c region, mainly. Ortega et al. (2003) recorded a large variability of the weed seed soil bank at a depth of up to 0.025 m in the time of germination, in viability and dormancy based on weed species, too. Its spatial variability was connected with the soil characteristics. Furthermore, Tyšer (2002) proved a statistically signiﬁ cant ﬂ uctuation of the weed seed soil supply within one vegetative period. During the autumn sampling of soil, a larger amount of whole
The yield losses in potato crop caused by weed infestation vary from 10-80% (Malik, 1995). Learning to identify a weed is a first step towards its control in the crop associated. In Pakistan, potatoes are mainly infested with the Amaranthus spp., Anagallis arvensis L., Avena fatua L., Chenopodium album L., Cirsium arvense (L.) Scop., Convolvulus arvensis L., Cynodon dactylon (L.) Pers., Cyperus esculentus L., C. rotundus L., Portulaca oleracea L., Sonchus oleraceus L., Solanum nigrum L., S. sarrachides and Sorghum halepense (L.) Pers (Malik, 1995).
10 Read more
Soybean suffers from heavy weed competition especially in the early growth stages hence early herbicidal control seems to be a must in this crop for harvesting acceptable yields. Unavailability of adequate laborers at peak period of weeding and unpredictability of rains along with non workable soil conditions; weed management in soybean is really a challenging task. Manual weeding is effective but it is cumbersome, time consuming and uneconomical while mechanical means generally leads to root injury. Under such situation weed management through the herbicidal application remains the only viable option. Spraying of pre- emergence herbicides helps to minimize the crop weed
The plant protection carried out in the Danish crop rotation experiment has not been sufficient to avoid the presence of weeds, pests and diseases. In some cases, there has been a tendency towards a difference between the treatments. It is not yet possible to conclude much about the crop rotations or the other experimental treatments in the experiment: presence or absence of catch crops and manure. In addition to this, the experimental treatments might influence the results of the crop protection: for example the presence of a catch crop reduces the possibilities of mechanical weed control.
11 Read more
yield. These results are also in agreement with Singh and Shashi (2012) who claimed that variation in tomato yield in different cultivars could be due to hereditary characteristics and higher nutrients translocation potential. Interaction between W x V showed (Table-2) that all tomato cultivars produced maximum fruit yield when applied weed management techniques as compared with control plots.
vital role in weed control and weeds are causing drastic yield loss, in Ethiopia, only few pre-emergence herbicides have been introduced and registered against major weeds in maize. Farmers practice cultural methods and used available herbicides repeatedly that has its own backstop. Continuous use of same herbicide for years may create resistance or hardening in weeds plants against that herbicide which reduce herbicide efficacy and the use of alternate herbicides avoids the development of herbicide resistance Owen et al. . Similarly, hand weeding is laborious, time consuming and difficult to practice in large scale farming. For this reason, there is a need to find and evaluate new pre- emergence herbicides for weed control in maize field at western Oromia, Ethiopia. Having above mentioned points the field experiment was conducted to evaluate the efficacy of different newly introduced pre-emergence herbicides (Lunar 537.5 SE + Venus 500 SC) with already registered and commonly used herbicide (Primagram Gold 660sc) for the control of major weeds in maize under field condition at Bako, West Shoa, Ethiopia.
al., 2011) while in Khyber Pakhtunkhwa,38% losses have been recorded (Hassan and Marwat, 2001). Marwat et al. (2011) is of the view that un-checked weeds in the field reduce the economic yield by up to 70%. The farmers in our country are mostly poor and they have very small land holding due to which, they don’t consider weeds as a serious issue. They have livestock’s at home so they preferably don’t control the weeds in the initial stages because they are interested in the biomass of the weeds to feed their animals. As a result the farmers unknowingly increase the weed seed bank in the soil for crops other than the fodder crops.
11 Read more
The investigations were planned with four large and fairly equal field experiments with different growing conditions on silty sand to loam type, erosion exposed soils. Experimental factor 1 was post harvest stubble treatments about 4 weeks after harvesting to prevent dissemination from the weed seeds and growth of the weed organs for propagation and storage of nutriment. Experimental factor 2 was the main soil preparation by 9-11 soil preparing methods or tools in autumn or spring, which, among others, have the purpose to bury and kill both annual weeds and perennial weeds before sowing in the spring. The results were registered by counting the surviving weeds in their young stage and, just before harvesting, by assessing the total amount of weeds, couch grass and surviving ley grasses from the previous years. Methods and reliability of assessing biological data are described by HOLMØY (1966). The yield was registered by weighing. The investigation fields were as follows: One field at the farm Teslo in the village Brandbu, Norway, at silty sand. Investigations started in spring 1993. Open field (that means not used for ley) in the years before start.
72 Read more
The effective weed control at narrow intra-row spacing of 15 cm resulted in increased growth and yield of groundnut in both years. This may be attributed to the reduced weed competition for resources such as light, nutrient, space and water achieved by the smothering effect of groundnut on late emerging weeds at narrow compared to wide plant spacing. These results are in agreement with that of Na-Allah et al. (2017) where cowpea spaced at 20 cm suppressed weed growth with consequence higher crop growth and yield than spacing of 30 cm. There were two obvious advantages in the close spacing. First, there was early and better canopy formation for effective weed smothering and suppression, coupled with higher plant population for enhanced productivity. The increase in pod number per plant in wide intra row spacing, however, may be the result of availability of better resources to the individual plants. Also narrow spacing might cause mutual shading which may cause floral abscission and pod dropping in the canopy strata. Nevertheless, in both years of this study, narrow intra-row spacing gave higher pod yield using higher plant population advantage which more than compensated for the reduction in pod yield of individual plants.
11 Read more
In contrast to spring-tine weeding, inter-row hoeing is a selective method of mechanical weed control (Rasmussen, 1993a, 1993c). Also, inter-row hoeing is particularly effective at controlling mature weeds (Böhrnsen, 1993; Morrish, 1995), whereas spring-tine weeding is most effective when weeds are small and consequently more vulnerable to soil cover (Wilson et al., 1993; Böhrnsen, 1993). Work by Hammarström et al. (1993) demonstrated that hoeing winter wheat with ducks-foot blades at a 25 cm row spacing could reduce the density of weeds between the rows by 82% and weed biomass by 35%. The weed density in the crop row was reduced by 25%. He also found that it was possible to hoe at a normal crop row spacing of 12.5cm using a rotary hoe. At this row spacing, weed density was reduced by approximately 45% between the rows and 25% in the rows. Crop yields were slightly increased as a result of hoeing with both the ducks-foot blades and the rotary hoe when compared with the unweeded control sown on 12.5cm rows, although the increases were not statistically significant.
39 Read more
Potato (Solanum tuberosum L.) is an important crop and is grown for human and animal consumption in Iran. The Ardabil province locates in the northwest of Iran, and includes about 15% of the total cultivation area in Iran (Anonymous, 2008). Weeds are one of the most important factors in potato production in Ardabil, Iran. Weeds cause yield losses worldwide with an average of 15 to 20% despite weed control applications (Nouri-Ghanbalani, 2002). Therefore, weed control is an important management practice for potato production that should be addressed to ensure optimum yield. Weed
In Europe, glyphosate resistant populations have developed in some weed species in perennial crops, includ- ing three species of the genus Conyza documented by the International Survey of Herbicide Resistant Weeds. Conyza spp. biology is reviewed in this paper and related to population dynamics and the development of resist- ant populations. Suboptimal growth stage at application, improper agricultural practices such as overreliance on glyphosate and long-term use of sublethal doses are identified as the most important factors of resistance development. Current control methods in perennial crops including mixtures of glyphosate with other active ingredients are discussed and effective weed management strategies are described to manage the development and spread of glyphosate resistant Conyza spp. in Europe.
10 Read more