It is a "beauty" and a "devil". The "domineering methods" of Canada goldenrod are exposed

Canada goldenrod, as its name suggests, is not a native plant of my country. But its origin is not only Canada, but also includes the United States, Mexico and other places in North America. In my country, after Canada goldenrod escaped into the wild, in addition to killing more than 30 species of wild native plants, it also invaded orchards, farmlands, tea gardens, vegetable fields, etc., causing many crops and cash crops to reduce or even die. In just over a decade, it has invaded more than a dozen provinces and cities in China, becoming a household name as "crazy goldenrod", "beautiful pest", "devil overlord flower" and "ecological killer".

In 2010, the Ministry of Environmental Protection (now the Ministry of Ecology and Environment) listed Canada goldenrod in the "List of Alien Invasive Species in China" (the second batch). After years of pursuit and interception, the occurrence of Canada goldenrod is basically under control, but this year, this beautiful alien invasive plant has become rampant again. On November 12, the topic "Wuhan citizens please report if you see this yellow flower" became a hot search on Weibo. After that, more than a dozen provinces and cities including Henan, Zhejiang, Jiangxi, Anhui, Hunan, and Jiangsu reported the outbreak and control of Canada goldenrod. Canada goldenrod has once again become a "star plant."

So, how did Canada goldenrod invade China?

△The wildly growing Canada goldenrod

The Beauty Trap

Canada goldenrod is a "petite jade" flower. Its yellow flowers are not very big, only 4-6 mm, but they bloom in clusters. When in full bloom, clusters of yellow flowers face the sky, which is the most pleasing to the eye. People like to plant it in the garden to appreciate it, and they also cut the flowers and put them in vases to decorate the living room and bedroom. In flower shops, it is also an ideal flower for flower arrangements.

It is because of this beauty that Canada goldenrod, which is far away in North America, has successfully attracted the Chinese. In 1935, Canada goldenrod was introduced as an ornamental plant into the courtyards of Shanghai and Jiangsu in my country. The beautiful little yellow flower has lived quietly in the courtyards and gardens of my country for decades, enjoying people's appreciation and praise.

△Bees collecting honey

I don't know when they slowly crossed the fence and no longer needed the care of the gardener. Around 1996, a small number of Canada goldenrod appeared in the coastal areas of Zhejiang Province. This appearance, in addition to allowing passers-by to appreciate the beauty of the delicate yellow flowers, did not bring any warning to people. People never thought that in just a few years, Canada goldenrod quickly occupied river beaches, wastelands, no-till land, both sides of railways and highways, rural roadsides, around houses, green land, and then further invaded orchards, farmlands, orchards, pastures and other places.

It was only at this time that people discovered that the beauty flowers in the courtyard were no longer "little yellow flowers in the greenhouse" but had become tall, thick, and difficult-to-remove malignant weeds.

The Devil's Tyrannical Means

Such rapid expansion is impossible without ruthless means. After escaping to the wild, Canada goldenrod showed super strong environmental adaptability and can grow on almost all types of land. Moreover, after arriving in China, it is no longer restricted by natural enemies in its place of origin. The unrestrained Canada goldenrod unscrupulously occupies more and more territory. Its growth rate is also very fast. The plant will quickly increase in height, up to 3 meters, occupying the upper space, blocking the sunlight on which other plants depend for survival, causing it to grow slowly and die.

△Canada goldenrod beside the road

In addition, it has three other means of rampant dominance, namely sexual reproduction, asexual reproduction and allelopathy. Among them, the combined effect of allelopathy and asexual reproduction allows Canada goldenrod to gradually expand from point to surface. Sexual reproduction can achieve long-distance diffusion.

▍Strong allelopathic effect

Allelopathy refers to the process in which plants release specific metabolites into the environment during their growth and development, changing the microecological environment around them, affecting the growth and development of other plants around them, and causing mutual exclusion or promotion among plants.

The allelopathic effect of most plants is inhibition, which is also one of the powerful invasion methods of many invasive alien plants. Canada goldenrod has such a super ability. When it settles in a new place, its roots will secrete some inhibitory substances. These inhibitory substances can inhibit the germination and growth of other herbaceous plants, gradually eliminate the surrounding native plants, and form a single Canada goldenrod growth area.

△Canada goldenrod around the house (seedling stage)

▍Spread of underground rhizomes

In addition to allelopathic effects, the rhizomes of Canada goldenrod can continuously grow new plants, helping it to crowd out other plants. This method of reproduction is called asexual reproduction.

The root system of Canada goldenrod is extremely developed. Each plant has 4 to 15 underground rhizomes that grow radially in all directions, and the longest rhizome can be more than 1 meter long. Each rhizome has multiple branches, and each branch has a bud at the top. These buds will grow into independent plants in the second year. We can calculate how many plants a Canada goldenrod will become in one year, and what about in two years? Canada goldenrod grows in patches, and the roots are intertwined with each other, so there is no room for other plants to grow!

▍Long-distance spread of sexual reproduction

The seeds of Canada goldenrod are pappus-shaped achenes, each with a small "parachute" attached to it, just like dandelion seeds, which can easily fly several kilometers away with the help of wind. After being eaten by birds, the seeds may be spread far away with the bird's feces. If these "flying" seeds fall on transportation and transport vehicles, they may be carried to even farther places.

△Bouquet of Canada goldenrod

The seeds of Canada goldenrod not only fly, but also have a huge amount of seeds. Each plant has countless capitulums, which aggregate into panicles. After pollination, each plant can produce more than 20,000 seeds. Under natural conditions, the seedling rate is between 50% and 80%. What a terrible number!

In addition to natural spread, human activities are also the culprit for the "rampant" spread of Canada goldenrod. For example, artificial introduction and cultivation for ornamental purposes, and the sale of fresh cut flowers are all possible causes of spread. In the process of transporting seedlings, its rhizomes or seeds may also be carried along for spread. The spread of seedlings during transportation is unintentional, more secretive, and can spread across cities and provinces.

Encircle it

The prevention and control of Canada goldenrod requires the efforts of the entire nation!

Just as the saying goes, "Wuhan citizens please report this yellow flower if you see it", only when the whole nation pays attention and reports it immediately when it is discovered, will the goldenrod be nowhere to hide.

In areas where Canada goldenrod occurs, a series of physical measures can be used for prevention and control, such as pulling out, burning, and cutting the ears. Canada goldenrod is easiest to identify during the flowering period, and it is the best time to prevent and control it because it has not yet produced fruits and seeds. At this time, it can be manually pulled out, and all rhizomes should be dug out and burned; for plants that have entered the fruiting period, the ears should be cut off first, wrapped in plastic bags and disposed of to prevent the spread of seeds.

△The pappus-haired achenes of Solidago canadensis

For areas with a smaller damage area, the above measures are easy to implement and relatively effective. However, for Canada goldenrod that grows in patches, it is quite difficult. This is time-consuming and laborious, and it is not easy to pull it out cleanly. In this case, deep plowing is a good method. Canada goldenrod seeds are very small, so their ability to push the soil is weak. Deep plowing can turn its seeds into the soil below 5 cm, making it impossible for it to emerge from the soil. The number of seedlings in the spring of the following year will be greatly reduced, thereby effectively controlling its spread.

Chemical control is the most economical and effective means of controlling Canada goldenrod. During the seedling stage or before and after flowering, glyphosate and other lethal herbicides and their combinations can be used for control. However, chemical control will pollute the environment and have serious side effects, especially in farmland and cash crop fields. These agents may contaminate crops and further harm our bodies.

Biological control is the use of the relationship between biological species to suppress another or another type of organism with one or a type of organism. Its biggest advantage is that it does not pollute the environment. The biological control of Canada goldenrod is currently in the research and experimental stage, and is far from being able to control it in the wild. Some scholars have tried to use the characteristics of the local plant white hyacinthus to spread and entangle to curb the spread of Canada goldenrod in the hardest-hit areas. Some scholars have also found that some dodders can parasitize the above-ground parts of Canada goldenrod. There is competition between reeds and Canada goldenrod, and the relative competitiveness of reeds is greater than that of Canada goldenrod.

In addition, Canada goldenrod also has natural enemies, including a moth larvae that feeds on its leaves, a borer larvae, and eggs and adults of another insect in its stems. Hopefully, in the near future, Canada goldenrod will be defeated by biological control. ■

Written by Yang Hongzhen (Researcher at Beijing Museum of Natural History)

Editor/Liu Zhao New Media Editor/Lv Bingxin

Photo provided by Yang Hongzhen

Produced by: Science Central Kitchen

Produced by: Beijing Science and Technology News | Science Plus Client

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