Scientific and standardized prevention and control of willow catkins, a key local standard in Henan is released

In an interview held on October 15, Liu Peng and Li Ying reported on the challenges of controlling the fluffy catkins produced by willow and poplar trees, which plague numerous cities during late spring and early summer. These airborne particles can trigger various respiratory issues, and due to their flammable nature, there’s a risk of fire. To tackle this ongoing problem, the Henan province has officially published its new local standard, the “Comprehensive Prevention and Control Technical Regulations for Willow and Poplar Catkins” (referred to as the “Technical Regulations”), which is set to take effect on January 9, 2025.

The trees in question are dioecious, meaning they have separate male and female plants. Each spring, after pollination, the mature seed pods gradually split open, releasing white, fluffy hairs that carry seeds, which are dispersed by the wind. This phenomenon, commonly referred to as “willow and poplar catkins,” primarily occurs from March to May each year.

In recent years, various municipal landscaping agencies have implemented strategies such as replacing the troublesome female poplars and willows with male varieties, injecting growth inhibitors, and applying various chemical treatments. While some success has been noted, challenges remain due to high costs, complex methods, and potential negative impacts on tree growth.

The primary source of catkins in Henan comes from poplar trees. Since the implementation of the Grain-for-Green Program in the 1990s, the area planted with poplars has continued to expand, making them a dominant species in the province. Most of the early selected high-quality varieties were female, which has exacerbated the catkin issue as these trees have matured.

This spring, Henan experienced a particularly dry climate with a prolonged cold snap followed by a sudden rise in temperatures, leading to an increase in the production of catkins and extending the duration of the nuisance. This has significantly affected the daily activities and mobility of the public.

In response to these challenges, the Henan Forestry Bureau enlisted the expertise of the Henan Academy of Forestry Sciences, alongside several institutions, including Henan Agricultural University and Nanjing Forestry University. After five months of collaborative effort, the “Comprehensive Prevention and Control Technical Regulations for Willow and Poplar Catkins” was drafted and officially approved.

The Technical Regulations outline the types and patterns of catkin production, guiding principles and goals for prevention, source investigations, and control zoning. It categorizes areas into those requiring intensive control and those with general control measures, using the area of willow and poplar trees and the number of female plants to determine the level of intervention needed.

Additionally, the regulations mandate the establishment of catkin monitoring points in critical areas, employing both manual and video surveillance to monitor the growth and changes in the flowering states of female trees.

To effectively mitigate catkin production, the Technical Regulations propose several strategies, including adjusting tree species composition, utilizing male varieties, top-grafting, canopy pruning, creating mixed-species forests, managing soil and nutrients, and reforestation. Physical measures such as retention, spraying, humidifying, and cleaning, alongside chemical treatments like GA3 injections, are also recommended to reduce the impact of catkins on the daily lives and travel of residents.