It was slack season in the rural areas along the Yangtze River when an urgent notice pulled many villagers out of their leisure time and into action: Keep all eyes out for Canadian yellow flowers and kill them on site.

The species has received its Chinese name for the clusters of yellow flowers it produces in the fall. The rhizomatous plant, originating in North America and bearing the English name of Canadian goldenrod, is an invasive species in China. It can cause deep damage to the local ecological environment. However, both its innocuous name and the flowery top have lowered people's vigilance.

"It looks pretty," Cheng Lixing, a villager from Yingcheng, Hubei Province, told Beijing Review. "The bundles of blossoming yellow flowers create beautiful sceneries across the farmland. In the beginning, we used to treat it as an ordinary weed and didn't pay much attention to it."

The destructive power concealed behind its innocent pretense soon vexed the locals. The plant grows very tall, over 2 meters, and it's highly prolific, with one plant producing as many as 20,000 seeds. It's also aggressive. Wherever it goes, it loots water and nutrients from other plants, and crowds them out with its fast-sprawling roots, leaving no room for their survival.

"The plant can grow in almost any place as long as there is earth and water," Cheng said. "It spreads pretty fast. A small patch can soon expand to a very big one as the seeds, like those of dandelions, are dispersed with the help of the wind."

Never fading

The invasion reached a severe scale this autumn, not only in rural areas, but also in cities. The plant has been found along roadsides, swamps, unused land and greenbelts in over 10 provinces and municipalities. Local governments in these places have issued notices calling on people to clear it. In Wuhan, capital of Hubei, a 24-hour hotline was set up specifically for locals to report the location of the plant as soon as they spot it.

A special fund has also been allocated to clear out this "wanted criminal." Villagers in Liji Village in suburban Wuhan gathered in late October to battle the weed. They worked eight hours a day for over 20 days straight to pull out over 90 percent of the plants growing in the village. Authorities in Hukou in Jiangxi Province organized residents from 122 villages to delete the plant from existence. Specific working groups have been formed to manage the issue and are recruiting as many volunteers as necessary. On November 26, a policeman in Hubei was taking photos of the plant to record its location when he fell into a reservoir and lost his life.

Some experts, such as Wang Yi, a landscape engineer from Nanjing, capital of Jiangsu Province, believe these efforts may be too little and too late. Wang has been studying the species and working on effective ways to clear it for seven years. "Normally it takes years for an exotic plant to settle down in a new country," Wang said. "For the small number that do spread in an invasive way, earlier actions need to be taken to ensure containment. Otherwise, the invasion will reach a scale that is hard to control."

Being introduced into Shanghai as an ornamental flower in the 1930s, the Canadian goldenrod was found growing wild in eastern China in the early 2000s. A study in 2005 showed that the plant then occupied about 7,788 hectares in Shanghai alone, an area approximately the size of Hong Kong Island, and was responsible for the disappearance of over 30 local plant species. In 2006, neighboring Jiangsu and Zhejiang provinces reported respectively 16,667 and 11,191 hectares of the plant.

Wang and his coworkers have formulated a program to contain the spread of the plant. According to Wang, the best time of year to take action is in spring, when the plant's new sprouts can be killed by herbicides. Herbicides are still effective in

summer, when the plant is around shin-height; however, by the time it begins to flower in fall, the plant has already taken strong hold, rendering efforts to control it largely in vain. "The rampant spread of its seeds and vigorous rhizomes raise level of difficulty in containing the plant year by year," Wang said.

Growing like a weed

In recent years, traces of this ecological killer have been found in many cities in central China's Henan Province, indicating the weeds have spread further north to the Yellow River area.

"We don't encourage individuals to pull out the weeds by themselves as an improper technique may cause the seeds to scatter over the ground or be carried by the wind to other places," said Hu Hongjie, an official from the local forestry bureau in Zhoukou in Henan.

According to Hu, the correct method is to first cut and bag the upper part—containing the seeds—and then pull the lower part out by the roots. "As the roots usually penetrate deep into the ground, we sometimes use diggers," Hu said.

As the plant grows so easily in many environments, including barren land, some have suggested growing it in the desert as a method to deal with desertification. However, Li Jiamei, a professor of botany at Henan Agricultural University, revealed that even though it can grow on dry land, it still needs some water in order to sprout.

"In Canada and the United States, where the plant originates, it has native predators, which help to maintain a balance, but it meets no resistance in China," Li said. "If we also import its predators, we may cause unknown problems."

A bulletin on China's environmental conditions released in May shows that over 660 introduced invasive species have been found across China. Among these, 71 have posed threats or potentially threaten natural ecosystems and have been included in the List of Invasive Alien Species in China. Some of the species were brought to China as ornamental plants or for research, while others came incidentally through channels such as transportation and distribution. "Preventing the import of such plants at the earliest stage is crucial," Li said.

Yang Zhongqi, an expert from the Chinese Academy of Forestry, is not as pessimistic about the utilization of the weeds in China. "I believe that we can explore ways to turn the weeds into useful assets, such as by using them to transform saline-alkali soil," Yang said. "I don't agree with tagging it as a malignant weed. It just didn't grow in the right place." 

(Print Edition Title: A Thorn in the Eye)  

Copyedited G.P. Wilson

Comments to yuanyuan@bjreview.com