Pigweed is native to North America. Due to its strong invasive nature and fast reproduction, it is categorized as an international quarantine weed. There are a total of 41 species of pigweed worldwide. It was first discovered in Hangzhou, China in 1935. How many species are there in China? Let's find out together!
Pigweed (left) and three-leaf pigweed (right)
Classification of Pigweed in China
There are mainly two species of pigweed in China: common pigweed and three-leaf pigweed.
Distribution of Pigweed in China
Currently, it has been found in 15 provinces and regions in Northeast China, North China, Central China, and East China (Heilongjiang, Jilin, Liaoning, Inner Mongolia, Hebei, Anhui, Jiangsu, Zhejiang, Jiangxi, Hubei, Hunan, Sichuan, Guizhou, and Tibet), and has formed four diffusion centers in Shenyang, Nanjing, Nanchang, and Wuhan.
The Harm of Pigweed
1. It releases various allelopathic substances, which have inhibitory and repellent effects on grasses, composites, and soil animals.
It can cover and suppress native plants, causing damage to the original ecosystem and reducing agricultural yields.
Each plant can produce 70,000 to 100,000 seeds per year, which are dispersed by the wind.
The seeds have a lifespan of 30 to 40 years and can grow even in barren and dry land.
2. When consumed by cows, pigweed can cause a decrease in milk quality.
3. Pigweed pollen is the main pathogen of a series of allergic reactions in humans, known as hay fever.
Methods of Controlling Pigweed
Pigweed picture
(1) From an ecological perspective, corresponding natural enemies have been found (natural enemies: striped leaf beetle, pigweed leaf roller, pigweed thrips, pigweed fly, pigweed noctuid).
According to foreign reports, there are over 400 kinds of insects and fungi that feed on pigweed.
Some of the leaf-feeding insects that pass the full assessment include pigweed leaf roller, striped leaf beetle, and pigweed fruit fly.
These insects will be introduced and used after local biosafety assessment.
The pigweed leaf roller and widespread leaf beetle from North America have strong destructive power on pigweed.
They have strict host specificity in experiments, and their release will not pose a threat to non-target plants.
The Institute of Biological Control, Chinese Academy of Agricultural Sciences has achieved good results using the pigweed leaf roller imported from North America in Hunan.
(2) Benzadiazole, Huwei, Kelu, and Grass Star can effectively control the growth of pigweed.
The best time to control pigweed is when it reaches a height of 50 to 70 cm. The recommended herbicides are 2,4-D ester at a dose of 1500 to 2250 ml/ha, or 20% paraquat at a dose of 3000 to 3750 ml. At this stage, pigweed seedlings are mostly emerged, saving both pesticide and labor.
(3) Shenyang Agricultural University and the Liaoning Provincial Highway Administration cooperated in establishing 200 ha of pigweed replacement control demonstration areas on the sides of Shenda and Shentao highways in 1989 and 1990.
The selected replacement plants include purple locust and seabuckthorn, which have economic value, and have achieved good results.
(4) Manual removal. Pigweed seeds germinate in large numbers from mid-April to early May, and the period of vegetative growth is from May to mid-July.
After the summer solstice, as the daylight hours shorten, pigweed quickly enters the flowering stage. The best time to eliminate it is before it produces seeds.
