Emergence Pattern and Periodicity of Palmer Amaranth (Amaranthus palmeri) Populations from Southcentral Great Plains

Evolution of multiple herbicide-resistant Palmer amaranth warrants the development of integrated strategies for its control in the Southcentral Great Plains (SGP). In order to develop effective control strategies, an improved understanding of the emergence biology of Palmer amaranth populations from the SGP region is needed. A common garden study was conducted in a no-till (NT) fallow field at Kansas State University Agricultural Research Center near Hays, KS, during 2018 and 2019 growing seasons, to determine the emergence pattern and periodicity of Palmer amaranth populations collected from the SGP region. Nine Palmer amaranth populations collected from five states in the SGP region: Colorado (CO1, CO2), Oklahoma (OK), Kansas (KS1, KS2), Texas (TX), and Nebraska (NE1, NE2, NE3) were included. During the 2018 growing season, the CO1 and KS1 populations displayed more rapid emergence rates, with greater parameter b values (−5.4, and −5.3, respectively), whereas the TX and NE3 populations had the highest emergence rates (b = −12.2) in the 2019 growing season. The cumulative growing degree days (cGDD) required to achieve 10%, 50%, and 90% cumulative emergence ranged from 125 to 144, 190 to 254, and 285 to 445 in 2018 and 54 to 74, 88 to 160, and 105 to 420 in the 2019 growing season across all tested populations, respectively. The OK population exhibited the longest emergence duration (301 and 359 cGDD) in both growing seasons. All tested Palmer amaranth populations had peak emergence period between May 11 and June 8 in 2018, and April 30 and June 1 in the 2019 growing season. Altogether, these results indicate the existence of differential emergence pattern and peak emergence periods of geographically-distant Palmer amaranth populations from the SGP region. This information will help in developing prediction models for decision-making tools to manage Palmer amaranth in the region.

Seedbank persistence and emergence pattern of Argemone mexicana, Rapistrum rugosum and Sonchus oleraceus in the eastern grain region of Australia

A thorough understanding of the emergence pattern and persistence of weed seeds is a prerequisite in framing appropriate weed management options for noxious weeds. In a study conducted at the University of Queensland, Australia, the emergence and seed persistence behavior of three major weeds Sonchus oleraceous, Rapistrum rugosum, and Argemone mexicana were explored with seeds collected from Gatton and St George, Queensland, Australia, with an average annual rainfall of 760 and 470 mm, respectively. Seed persistence was evaluated by placing seeds at the surface layer (0 cm) or buried at 2 and 10 cm depths enclosed in nylon mesh bags and examined their viability for 42 months. In another study, the emergence pattern of four populations, each from these two locations, was evaluated under a rainfed environment in trays. In the mesh-bag study, rapid depletion of seed viability of S. oleraceous from the surface layer (within 18 months) and lack of seed persistence beyond two years from 2 and 10 cm depths were observed. In trays, S. oleraceous germinated 3 months after seeding in response to summer rains and there was progressive germination throughout the winter season reaching cumulative germination ranging from 22 to 29% for all the populations. In the mesh-bag study, it took about 30 months for the viability of seeds of R. rugosum to deplete at the surface layer and a proportion of seeds (5 to 13%) remained viable at 2 and 10 cm depths even at 42 months. Although fresh seeds of R. rugosum exhibit dormancy imposed due to the hard seed coat, a proportion of seeds germinated during the summer months in response to summer rains. Rapid loss of seed viability was observed for A. mexicana from the surface layer; however, more than 30% of the seeds were persistent at 2 and 10 cm depths at 42 months. Notably, poor emergence was observed for A. mexicana in trays and that was mostly confined to the winter season.

Short communication: A predictive model for the time course of seedling emergence of Phalaris brachystachys (short-spiked canary grass) in wheat fields

Aim of study: A predictive model of the seedling emergence pattern of Phalaris brachystachys Link (short-spiked canary grass) was developed, aimed to contribute to support a more efficient management of this troublesome, competitive weed in winter cereal crops around its native Mediterranean range and in different areas of the world where it is introduced. Area of study: Southern (Andalusia) and northern Spain (Navarra). Material and methods: A model describing the emergence pattern of P. brachystachys in cereal fields based on accumulation of hydrothermal time in soil was developed and validated. For model development, cumulative emergence data were obtained in an experimental field, while an independent validation of the model was conducted with data collected in two commercial wheat fields from climatically contrasting regions of Spain. Main results: The relationship between cumulative emergence and cumulative hydrothermal time (CHT) was well described by a Logistic model. According to model predictions, 50% and 95% seedling emergence takes place at 108 and 160 CHT above base water potential for seed germination, respectively. The model accurately predicted the seedling emergence time course of P. brachystachys in the two commercial wheat fields (R2 ≥ 0.92). Research highlights: This model is a new tool that may be useful to improve the timing of control measures to maximize efficiency in reducing P. brachystachys infestations in cereal crops.

One-Year and Ultimate Reserve Risk in Mack Chain Ladder Model

We investigate the relation between one-year reserve risk and ultimate reserve risk in Mack Chain Ladder model in a simulation study. The first goal is to validate the so-called linear emergence pattern formula, which maps the ultimate loss to the one-year loss, in case when we measure the risks with Value-at-Risk. The second goal is to estimate the true emergence pattern of the ultimate loss, i.e., the conditional distribution of the one-year loss given the ultimate loss, from which we can properly derive a risk measure for the one-year horizon from the simulations of ultimate losses. Finally, our third goal is to test if classical actuarial distributions can be used for modelling of the outstanding loss from the ultimate and the one-year perspective. In our simulation study, we investigate several synthetic loss triangles with various duration of the claims development process, volatility, skewness, and distributional assumptions of the individual development factors. We quantify the reserve risks without and with the estimation error of the claims development factors.

Seed Longevity and Seedling Emergence Behavior of Wild Oat (Avena fatua) and Sterile Oat (Avena sterilis ssp. ludoviciana) in Response to Burial Depth in Eastern Australia

Weed emergence time and the longevity of weed seeds within the soil play an important role in implementing a timely and effective weed control program. In this study, the seed longevity and emergence pattern of wild oat (Avena fatua L.) and sterile oat [Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne] were monitored in field conditions. Fresh seeds of A. fatua and A. ludoviciana were placed into nylon bags (50 seeds per bag in three replications for three locations in Southeast Australia: Gatton, Narrabri, and St. George) and buried at depths of 0, 2, and 10 cm in November 2017. Bags were exhumed at 6-mo intervals over 30-mo to evaluate seed germination, viability, and decay components. The seed decay component of A. fatua and A. ludoviciana followed an exponential pattern. On both the surface and at the 10 cm burial depth, 50% of the seeds of A. fatua and A. ludoviciana had decayed by 6-mo. The seeds of A. fatua persisted longer at 2 cm depth than at other depths, particularly at St. George where 90% of the seeds decayed after the 30-mo study. However, at Gatton and Narrabri, 90% of the seeds of A. fatua at this depth had decayed after 18-mo of seed placement in the soil. In the emergence pattern experiment, the emergence of A. fatua and A. ludoviciana from different burial depths was also studied (2017-2019). The emergence of A. fatua and A. ludoviciana was greater from 2 cm (29-36%) and 5 cm (18-43%) soil depths compared to the surface (5-10%) and 10 cm (3-9%) soil depth. A. ludoviciana emerged earlier (2253 growing degree days, GDD; March 14, 2018) than A. fatua (3364 GDD; May 23, 2018). Both species exhibited high emergence between May to June 2018, and the last cohort of each species was observed in October 2018. The highest seedlings emergence occurred at the start of the winter season (May), which emphasizes the need for early PRE weed control such as tillage, herbicide application, and cover crops to ensure crops are planted in a clean seedbed. The continued emergence of these weeds into the spring season (October) emphasizes the need for extended periods of A. fatua and A. ludoviciana management. The results also suggest that management strategies that can control all emerged seedlings over two years and restrict seed rain in the field could lead to complete control of Avena spp. in the field.

A CBCT aided assessment for the location of mental foramen and the emergence pattern of mental nerve in different dentition status of the Saudi Arabian population

Objective: The anatomy of mental foramen (MF) is a noteworthy landmark during any surgical procedures in the inter-foraminal region. Thus, the study aims at evaluating the location of MF and the emergence pattern of MN in three status of dentition in Saudi Arabian population. Material and Methods: In a prospective study, we have analyzed 240 cone beam computed tomography (CBCT) for the location of MF and the emergence pattern of MN. The study comprising three groups, namely dentulous, partially edentulous and edentulous, each having eighty CBCT scans. We presented the data in percentages. The chisquare and McNemar’s test were used for testing association and pair-wise analysis, respectively. Results: The most common location of MF was below the apex of the second premolar irrespective of dentition status, with 54.2% in right and 60% in the left side of the jaw. Among the dentition status, left side of the mandible has shown significant variation for the location of MF, whereas gender and age showed variation in the right side. Anterior loop (AL) (Type-III) the emergence pattern of MN was the highest in all dentition status, with 51.7% in right and 53.8% on the left side. The variation in the emergence pattern of MN in terms of gender and side of the jaw was statistically significant. Conclusion: In the Saudi Arabian population, the apex of second premolar and type III/AL was the most prevalent location of MF and the emergence pattern of MN, respectively. KEYWORDS Anterior loop; Cone beam CT; Mandible; Mental foramen; Mental nerve.

Emergence pattern of Palmer amaranth (Amaranthus palmeri) influenced by tillage timings and residual herbicides

The evolution of multiple herbicide-resistant weeds, including Palmer amaranth, has necessitated the implementation of an integrated weed management (IWM) program. Understanding weed emergence patterns is critical for developing effective IWM strategies. The objective of this study was to evaluate effect of tillage timings and residual herbicides on cumulative emergence and emergence pattern of Palmer amaranth. Field experiments were conducted in 2015 and 2016 in a field naturally infested with photosystem (PS) II and 4- hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor-resistant Palmer amaranth near Shickley, Nebraska in a bare ground study, with no crop planted in the plots but residues from the preceding corn crop were present on the soil surface. Treatments consisted of shallow tillage timings (early, mid, and late), three premix corn or soybean residual herbicides, and a nontreated control. The Weibull function was fitted to cumulative Palmer amaranth emergence with day of year (DOY) and thermal time (TT) as independent variables. Year by treatment interaction was significant for time to 10%, 25%, 50%, 75%, and 90% Palmer amaranth emergence and cumulative emergence. Majority of Palmer amaranth seedlings emerged early, following early-tillage with 90% cumulative emergence occurring on DOY 172 compared with DOY 210 to 212 for mid- and late-tillage and DOY 194 in nontreated control in 2015. In 2016, 90% of cumulative emergence following early-, mid-, and late-tillage (DOY 201 to 211) were similar, and nontreated control (DOY 188) was similar to early-tillage. Nontreated control and PRE herbicide treatments had similar DOY values for 90% emergence in both years. Number of emerged Palmer amaranth seedlings over the season was higher with shallow tillage than no tillage or with PRE herbicides.

Seasonality in the production of male larvae: a game model for parasitic barnacles (Cirripedia: Rhizocephala)

The male larvae of many parasitic barnacles are planktonic and are seasonally released. To achieve reproductive success, a male must be accepted by a receptive female that has successfully infected a host. To understand the seasonality of the breeding biology of parasitic barnacles, we developed an evolutionary game theoretical model for the seasonal pattern in the production of male larvae. Assumptions are that female parasitic barnacles become receptive following a given seasonal pattern. The parental females (mothers) choose the timing of producing their own male larvae to achieve maximum reproductive success. In the evolutionarily stable seasonal pattern, the production of male larvae often shows a sharp peak on a single day, indicating strongly synchronized production of male larvae, even when the supply of receptive females is distributed over the breeding season. When the total number of male larvae is large, the evolutionarily stable male production pattern may include multiple peaks, but it never shows a continuous distribution. This is very different from the game model previously developed for the emergence pattern of butterflies, where evolutionarily stable male emergence is always continuously distributed over a fraction of the mating season. As planktonic larvae, male parasitic barnacles have a naturally limited ability to find receptive females, and females may stay receptive for many days, whereas in butterflies, newly emerged females are mated within a day of their emergence.