What is the basis for the classification of weeds?

Example sentences: 1Weeds must be removed from this land. 2.This weed must be removed.

Detailed explanation:1All kinds of grasses. "Hanshu Western Regions Biography on the Popin Kingdom": "Popbin is flat, mild, with mesh, weeds and strange trees, sandalwood, skull, catalpa, bamboo, lacquer. ”

2.Refers to weeds. Southern Dynasty Liang Jiangyan "Ode to Grass and Trees: Fir": "The trees look down, and the weeds do not peep." "Speech at the Meeting of Secretaries of Provincial, Municipal and Autonomous Region Party Committees": "There are two kinds of things growing in the fields, one is called grain and the other is called weeds. ”

Definition: A broad definition of weed refers to any plant that grows on a site that is detrimental to human activity or harmful to production sites. It is mainly herbaceous, but also includes some small shrubs, ferns and algae.

There are more than 300,000 species of plants that have been named in the world, and about 8,000 species of plants that have been identified as weedsThere are more than 36,000 plant names that can be found in books and periodicals in China, and more than 1,200 kinds of plants in 119 families are identified as weeds. In addition to being classified according to botanical methods, it can also be divided into aquatic, swamp, wet and xerophytic according to its adaptability to water, and can be divided into grasses, sedges and broad-leaved grasses according to the needs of chemical control, and can also be classified according to the nutritional type, growth habits and reproduction methods of weeds. Its biological properties are as follows:

There are many modes of dispersal, strong reproduction and regeneration, and weeds.

Weed. The life cycle is generally shorter than that of crops, mature seeds fall as they ripen, have strong stress resistance, and high photosynthetic efficiency. The main pests of weeds in farmland are:

Competing with crops for nutrients, water, sunlight and space, hindering the ventilation and light transmission of the field, increasing the local climate temperature, and some are intermediate hosts of pests and diseases, promoting the occurrence of pests and diseasesParasitic weeds absorb nutrients directly from the crop, reducing the yield and quality of the crop. In addition, the seeds or pollen of some weeds contain toxins that can poison humans and animals.

The concept of weed is relative. For example, a dandelion is not a weed when it grows in a pot;But when grown in the wild, it becomes a weed.

"Weed" originally meant "useless or unbeautiful herbs".

In a broad sense, weeds are defined as all plants that grow on sites that are detrimental to human activities or harmful to production sites. It is mainly herbaceous, but also includes some small shrubs, ferns and algae.

The germination, flowering, fruiting, and the entire life cycle of annual weed seeds are completed within one year, and this type of weed is propagated by seeds, and the seedlings cannot overwinter and only bear fruit once a year. Such as golden dogtail, quinoa, amaranth, xanthium, etc.

Perennial weeds survive in the field for more than 3 years and can flower and bear fruit several times a year. The overwintering buds, rhizomes, tubers, roots and bulbs of these weeds overwinter in the soil, such as eye cabbage. In recent years, it has occurred in large numbers in farmland, causing serious harm and difficult to prevent.

Such as rhizome weeds (horsetail, etc.), root and bud weeds (lettuce, bitter weed, etc.), straight root weeds (sheep's hoof, etc.), bulb weeds (fragrant aconite).

Poaceous weeds are the main weeds in paddy and upland fields, and there are annual and perennial weeds. If the seeds are large, it is difficult to control herbicides on the soil surface, such as wild millet and double-spike paspalum. If the seed grain is small, the herbicide treated with soil surface has a good control effect, such as barnyard grass, dogtail grass, etc.

Broadleaf weeds, also known as cotyledonous weeds, can be divided into annual weeds and perennial weeds according to the length of its life. Annual broad-leaved weeds are propagated by seeds, and germinating weeds in shallow soil can be effectively controlled when herbicides are controlled, such as quinoa, amaranth, camelina and wild watermelon seedlings. For the weeds germinating in the deep soil layer, because the seeds are below the medicine layer, it is difficult to control the herbicides with soil surface treatment, such as Xanthus, duck plantar grass, hemp, etc.

This type of weed requires two full summers to complete its growth cycle. Seed propagation, generally germinate in summer and autumn, overwinter with seedlings or roots, and bloom and bear fruit in the summer and autumn of the following year, but there are also spring germination, flowering and fruiting in the current year, and the whole life cycle spans two years. Such as Artemisia annua, Artemisia niordi, etc.

However, there are also spring sprouts, flowering and fruiting in the same year, showing the habit of being an annual. Such as shepherd's cabbage, look at Mai Niang, etc.

The germ of the sedge weed has a cotyledon (seed leaf), usually narrow, long, with parallel veins, without petioles, with leaf sheaths wrapped, without leaf tongues, and the stems are three-edged, usually hollow, without nodes. It occurs mainly in rice fields. It has many types, many quantities, and serious harm, and it is difficult to prevent agricultural and chemical agents.