WEEDS AND PREVENTION MEASURES

I. THE CONCEPT OF WEEDS          

            Weeds are plants that grow where humans do not need them. A plant may be a weed in one place, but it is a useful plant in terms of providing nutrients or nourishment to humans elsewhere.

II. HAZARDS OF WEED

            1/ Weeds reduce crop yield and quality

            Weeds compete with plants for light, nutrients and water, making plants unfit for living, so their growth and development are poor, yield is low, and the quality of agricultural products is also reduced.

            2/ Weeds are hosts of pests:

            Plants of the same family, order or having plant-like characteristics are very good secondary hosts for pests. In addition to being a host, weeds also create suitable ecological conditions for the development of pests and diseases. The field has a lot of weeds, the humidity and temperature also change, often more favorable for the development of pests.

            3/ Weeds can contain harmful toxins:

            There are weeds that can contain toxins that affect plants. Often these weeds can contain toxins such as cyanhydric acid, alkaloids or oxalates.

            4/ Weeds increase the cost price of the product.

            The removal of weeds requires additional costs and the means of machinery, fuel, and chemicals have increased costs and increased cost price in agricultural production.

            5/ Weeds affect traffic:

            Weeds in rivers and irrigation works obstruct the movement of ships, affecting the conduction of water into the fields.

III. CLASSIFICATION OF WEEDS

            Weeds can be classified in many ways: by growth cycle, by topography, by mode of life, by degree of toxicity, by morphology, by plant type characteristics, etc.

1. Classification by growth cycle:

            According to this classification, in the tropics there are two groups of weeds: annuals and perennials.

            Annual weeds: are weeds that complete their life cycle (from seed, germinating to seed) in one or two growing seasons in a year. These weeds usually die in the dry season after completing their life cycle.

            Perennial weeds: are weeds that live longer than a year. Annually, the number of times of flowering and fruiting can vary from zero to several times depending on living conditions. Perennial weeds are often difficult to kill because of some of their morphological and physiological characteristics such as the length of the bulbs. , of branches, of underground stems and of roots that creep above ground; roots develop deeply, so it is difficult to be destroyed by tillage methods; strong asexual reproduction

2. Classification by mode of living

            According to this classification, weeds are classified into autotrophic and parasitic weeds. Most weeds are in the first group, they have enough nutritional organs such as roots to absorb water and mineral salts, leaves to photosynthesize...

3. Classification by morphology

            Weeds can be classified morphologically into narrowleaved weeds (also called monocots) and broadleaved weeds (also called dicotyledons).

           Monocotyledonous weeds have common characteristics such as: the leaves are often narrow, thick, obliquely grown, the leaf surface is hairy, the roots are usually cluster roots, shallow feeding, the growth apex is covered in the leaf sheath. However, in this group there are also some weeds with slightly different properties, such as the narrow-leaved sedge, which is soft and thin.

            Dicotyledons usually have broad, horizontal, thin and soft, hairless leaves; Roots are usually tap roots, deeply rooted, the growth apex is exposed.

4. Classification by flora.

            This classification is relatively easy to use in practice. According to this classification, the weeds are classified into three groups: Grass weeds, Sedge weeds, and broadleaved weeds.

a/ Group  of grass weeds:

            REPRESENTATIVE OF  GROUP OF GRASS WEEDS

Identifying characteristics:

          Stem: Leaves usually round, hollow inside

          Leaves: long, narrow leaf  plate, parallel veins. Leaves are attached to the stem in two rows.

b/ Group of sedge weeds:

GROUP OF SEDGE WEEDS

:            

Stem: usually hard, non-hollow, solid, with triangular angles.

Leaves : Leaves: long, narrow, parallel veins like grass weeds, leaves attached to the stem in three rows of spirals

c/ Group of broadleaved weeds:

 GROUP OF BROADLEAVED WEEDS       

Leaves: the leaf plate is usually wider than  grass weed and  sedge weed groups, the veins are arranged in different patterns: crow feet, spider webs, etc.

IV. CHARACTERISTICS OF WEEDS

1/ Weeds have many forms of reproduction:

            Plants usually have only one form of reproduction: either only asexual or only sexual whereas in weeds there are many more forms of reproduction. For example, Nut grass and Cogongrass have two forms of reproduction: by underground stem and by seed. Bermuda grass  has up to three forms of reproduction: by seed, by creeping stem and by underground stem.

2/ Weeds have a lot of seeds and a lot of dormant buds

3/ Weeds are deciduous and have many modes of propagation

           After ripening, the weed seeds easily fall off the tree and fall to the ground. This phenomenon is accompanied by the characteristic of uneven ripening, which prolongs the release time of the weeds. Weeds have many ways of spreading: by wind, by water, by animals, livestock, people, seeds, farming tools, etc.

V. WEED REPRODUCTION

1/ Sexual reproduction: Most weeds have seeds, weed seed is one of the genetic vehicles of the weed.

2/ Asexual reproduction: Many perennial weeds reproduce asexually, the forms of asexual reproduction in weed are:

            Reproduction through creeping stem on the ground: each end of the vine will produce a seedling, which will grow roots and attach to the ground. From this seedling will grow a creeping stem, creeping a piece will give a new seedling ( centilla ,creeping woodsorrel , etc. )

            Reproduction through rhizomes, underground stems: This weed has underground stems that grow, growing below the ground. These are Bermuda grass., Cogongrass, Blanket grass , etc.

            Reproduction through tubers: some weedes such as nut grass have underground stems that swell into tubers, on the tubers there are dormant buds protruding in holes. On the tubers can grow new roots and underground stem strips. In these underground stem strips, there are bulges that expand into tubers.

Reproduction through the bulb.

Reproduction by dormant buds on leaves or buds.

VI PREVENTION OF WEEDS

1. Precautionary measures:

             Use seeds that are not mixed with weed seeds.

             Farm tools must be clean of  weed seeds and stems.

             The banks of fields, canals and ditches need to be cleared of weeds.

             Cattle should be taken away from production fields because weed seeds in the digestive system and manure do not lose their germination power.

             Do not leave seed-producing weeds on the production field (uproot the weeds left after using herbicides)

 2. Measures of extermination

            Cultivation methods: hand weeding, tillage, field burning, appropriate water use

            Biological measures: using vegetation, using animals; goose, cow, sheep, fish

            Using chemical methods: the use of herbicides is now very popular in many countries and is considered the most effective weed control method.

Advantages:

            Not as hard as other methods

            It is specialized, so it has little effect on plants

            Can be used at different times

            Less labor intensive, quick to use on a large scale

            Reduce soil erosion.

Disadvantages:

            Requires proficiency in the use of products

            Specialized tools are required

            May cause damage to neighboring crops

            Can induce resistance in weeds