Modelling weed population dynamics: impact of cultural control and climate change

Over the last three decades, concern about food safety and the management of natural resources has increased. Instigated by the previous EU pesticide review, (EU 91/414) carrot growers in particular have been hit by the revocation of several post-emergence herbicides. There is real concern among growers that this may impair profits. To identify alternative weed control strategies, a modelling framework capable of simulating the impact of alternative weed management strategies on long-term weed population dynamics, was proposed. Scentless mayweed (Tripleurospermum inodorum) was chosen as model weed species. The system represented in ECOSEDYN (Effects of Cultural control and climate On SEedbank DYN For each component model in ECOSEDYN the literature was reviewed to identify the best mathematical representation and then the model was parameterised. To improve accuracy of model projections and address gaps in knowledge, field experiments were conducted in two areas: soil cultivation, and plant growth and reproduction. The results of the cultivation experiments revealed that key assumptions in models for weed seed re-distribution are incorrect. The experiments focusing on plant growth and reproduction resulted in a novel approach to the modeling of biomass increase, flowering and seed shedding where the different processes were quantitatively and temporally linked using Beta functions. amics), comprises a six-year crop rotation: one year of carrot and five years winter wheat and repeated four times. The weed management strategies consist of combinations of cultural control measures (sowing time and crop maturity time). In addition, the interaction of climate with the cultural control measures was assessed by implementing two future climate scenarios, (‘No change’ vs ‘Heating up’) based on weather data over the last 18 years. The results of the ECOSEDYN simulations showed that, regardless of the prevailing climate, choosing a fast maturing carrot cultivar is by far the most important factor in maintaining the weed seedbank low. In addition, the risk for higher seedbank levels in the long-term under ‘Heating up’ climate is largest if carrot is continuously sown late

Modelling weed population dynamics : impact of cultural control and climate change

Over the last three decades, concern about food safety and the management of natural resources has increased. Instigated by the previous EU pesticide review, (EU 91/414) carrot growers in particular have been hit by the revocation of several post-emergence herbicides. There is real concern among growers that this may impair profits. To identify alternative weed control strategies, a modelling framework capable of simulating the impact of alternative weed management strategies on long-term weed population dynamics, was proposed. Scentless mayweed (Tripleurospermum inodorum) was chosen as model weed species. The system represented in ECOSEDYN (Effects of Cultural control and climate On SEedbank DYN For each component model in ECOSEDYN the literature was reviewed to identify the best mathematical representation and then the model was parameterised. To improve accuracy of model projections and address gaps in knowledge, field experiments were conducted in two areas: soil cultivation, and plant growth and reproduction. The results of the cultivation experiments revealed that key assumptions in models for weed seed re-distribution are incorrect. The experiments focusing on plant growth and reproduction resulted in a novel approach to the modeling of biomass increase, flowering and seed shedding where the different processes were quantitatively and temporally linked using Beta functions. amics), comprises a six-year crop rotation: one year of carrot and five years winter wheat and repeated four times. The weed management strategies consist of combinations of cultural control measures (sowing time and crop maturity time). In addition, the interaction of climate with the cultural control measures was assessed by implementing two future climate scenarios, (‘No change’ vs ‘Heating up’) based on weather data over the last 18 years. The results of the ECOSEDYN simulations showed that, regardless of the prevailing climate, choosing a fast maturing carrot cultivar is by far the most important factor in maintaining the weed seedbank low. In addition, the risk for higher seedbank levels in the long-term under ‘Heating up’ climate is largest if carrot is continuously sown late.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Photoperiod sensitivity affects flowering duration in wheat

Flowering and successful pollination in wheat are key determinants of both quantity and quality of grain. Bread wheat line ‘Paragon’, introgressed with single or multiple day length insensitivity alleles was used to dissect the effects on the timing and duration of flowering within a hierarchical plant architecture. Flowering of wheat plants was observed in a series of pot-based and field experiments. Ppd-D1a was the most potent known allele affecting the timing of flowering, requiring the least thermal time to flowering across all experiments. The duration of flowering for individual lines was dominated by the shift in the start of flowering in later tillers and the number of tillers per plant, rather than variation in flowering duration of individual spikes. There was a strong relationship between flowering duration and the start of flowering with the earliest lines flowering for the longest. The greatest flowering overlap between tillers was recorded for the Ppd-1b. Across all lines, a warmer environment significantly reduced the duration of flowering and the influence of Ppd-1a alleles on the start of flowering. These findings provide evidence of pleiotropic effects of the Ppd-1a alleles, and have direct implications for breeding for increased stress resilient wheat varieties

A simple model to quantitatively account for periodic outbreaks of the measles in the Dutch Bible Belt

In the Netherlands there has been nationwide vaccination against the measles since 1976. However, in small clustered communities of orthodox Protestants there is widespread refusal of the vaccine. After 1976, three large outbreaks with about 3000 reported cases of the measles have occurred among these orthodox Protestants. The outbreaks appear to occur about every twelve years. We show how a simple Kermack-McKendrick-like model can quantitatively account for the periodic outbreaks. Approximate analytic formulae to connect the period, size, and outbreak duration are derived. With an enhanced model we take the latency period in account. We also expand the model to follow how different age groups are affected. Like other researchers using other methods, we conclude that large scale underreporting of the disease must occur

Analyses of the relationship between photoperiod sensitivity and flowering duration in wheat

Wheat lines differing in photoperiod sensitive allele were grown in pots under controlled and under ambient environment conditions. Flowering assessments included records of individual floret phenotype throughout the course of anthesis for the first 5 spikes per plant for each genotype. The plants under the controlled environment conditions were grown under two temperature regimes: cool and warm. The start and end of flowering for each spike and plant for each of the replicates for each genotype are given in addition to flowering duration for 2011 and 2012 (pot based ambient) and for 2012 (controlled environment)

Diversity for resilience : multi-scale application of agro-ecology

The integration of ecological principles into agricultural systems presents major opportunities for spreading risk at the crop and farm scale. This paper presents mechanisms by which diversity at several scales within the farming system can increase the stability of production. Diversity of above- and below-ground biota, but also genetic and phenotypic diversity within crops, has an essential role in safeguarding farm production. Novel mixtures of legume-grass leys have been shown to potentially provide significant benefits for pollinator and decomposer ecosystem services but to realise the greatest improvements carefully tailored farm management is needed such as mowing or grazing time, and the type and depth of cutivation. Complex farmland landscapes such as agroforestry systems have the potential to support pollinator abundance and diversity and spread risk across production enterprises. At the crop level, early results indicate that the vulnerability of pollen development, flowering and early grain set to abiotic stress can be ameliorated by managing flowering time through genotypic selection, and through the buffering effects of pollinators. Finally, the risk of sub-optimal quality in cereals can be mitigated through integration of near isogenic lines selected to escape specific abiotic stress events. We conclude that genotypic, phenotypic and community diversity can all be increased at multiple scales to enhance resilience in agricultural systems