Ragweed

2014 was the hottest year on Earth since recordkeeping began in 1880, and ten of the previous warmest years on record occurred since 2001. The scientific consensus is that climate change is the driving force behind these rising temperatures. Scientific studies have also shown that our changing climate could favor the formation of more ozone smog in some areas and increase the production of allergenic pollen such as that released by the ragweed plant, the principal source of pollen associated with allergic rhinitis.

This is bad news for allergy sufferers and asthmatics because both ragweed pollen and high levels of ozone smog can trigger asthma attacks and worsen allergic symptoms in adults and children. Moreover, studies show that people exposed to both ragweed allergens and ozone are likely to become more ill than people exposed to just one of the two. These negative health effects are expected to worsen if carbon dioxide (CO2) concentrations keep rising and climate change continues unchecked.

In order to understand the scope of this problem and who will be affected by it, the Natural Resources Defense Council has updated its groundbreaking 2007 Sneezing and Wheezing report, which mapped, for the first time, areas within the United States where ragweed and unhealthy ozone pollution overlap. This new report shows that one in three Americans, 109 million people in our country, are the most exposed to worsening respiratory allergies and asthma associated with climate change. Together, the findings that so many Americans face this double-whammy health risk provide evidence of the urgent need for taking action now to reduce the health threats posed by climate change.

Invasive species such as Ambrosia (an annual weed) pose a biosecurity risk whose management depends on the knowledge, attitudes and practices of many stakeholders. It can therefore be considered a complex policy and risk gover-nance problem. Complex policy problems are characterised by high uncertainty, multiple dimensions, interactions across different spatial and policy levels, and the involvement of a multitude of actors and organisations. This paper provides a conceptual framework for analysing the multi-level and multi-actor dimensions of Ambrosia management. Potential and existing public, private and public–pri-vate management strategies are identified to address the interests and needs of different actor groups across different levels. We conclude that policies that promote a mix of public and private Ambrosia management strategies may respond better to the needs and interests of different actor groups across different levels than a one-size-fits-all approach. However, multiple policy strategies need to be aligned in order to lead to synergies and spreading coherent messages to the public. Collaboration may enhance the likelihood of biosecurity management and risk governance of Ambrosia being adequately implemented and enforced.

A B S T R A C T Ragweed (Ambrosia artemisiifolia L.) is a noxious plant that not only is a troublesome agronomic weed that causes economic damage to agricultural crops but also − and even more importantly − causes severe health problems due to its severe allergenicity. The pollen of invasive ragweed has become a major allergenic risk factor in urban areas in newly occupied regions. Many urban areas prohibit herbicide application; thus, mowing is the most widely used control measure. Counting pollen is labour intensive; therefore, pollen production data are mainly based on estimations. Field experiments were conducted to determine the effects of different mowing scenarios, plant density and cutting height on the biomass, pollen production and seed production of common ragweed plants. Ragweed plants were mown twice: just before the flowering of terminal racemes (BBCH 59) and when the flowers of the re-sprouting lateral shoots reached BBCH 59. A 1-to 3-cm cutting height produced the greatest pollen reduction compared to that of intact control plants (94%) based on a season-long pollen collection. The number of female flowers also significantly decreased (97%). Compared to the control, the onset of pollen discharge was delayed by 5 weeks and the length of the pollen discharge period decreased from 9 to 4 weeks. The season-long unique and reproducible pollen production data can be integrated with airborne pollen modelling and population management strategies.