In every field, weeds are always present. But what exactly are weeds? Well, some people define weeds as an unwanted, undesirable and useless plant. But no plant is completely useless. We may then define weeds as plants that are unwanted at a particular time and place and whose economic use has not yet been discovered. A plant species can only be called as weed if humans have not yet found a use for it. “One man’s crop maybe another’s weed.”

Some plant species though occur 99% as weeds in some fields. Echinochloa spp. and Monochoria vaginalis in rice fields for example. R. cochinchinensis and Cyperus rotundus in corn and vegetable fields respectively are considered as weeds. 10% of the 300,000 angiosperm species behave as weeds 99% of the time.

The unique characteristics of weeds have made them difficult to control in the field. They have excellent adaptations to disturbed environment and occupy the ecological spaces left open in agroecosystems. Other characteristics of weeds include their rapid vegetative growth, reproduce rapidly and mature early, very prolific and produce plenty of seeds, can survive and adapt to adverse conditions, dormancy of propagules or can be induced to dormancy under favorable environments, and are adapted to crop competition.

Rapid Vegetative Growth and Reproduce Rapidly and Mature Early

Weeds have numerous tillers for grasses, rapid tuber and shoot formation for sedges, and faster stem elongation and branching for broad leaves. Also, weeds are able to reproduce sexual and asexually. These have allowed the weeds to be able to maintain high population densities if not managed effectively. They also mature early so they are able to reach their reproductive period at a lesser time, hence more plants capable of to reproducing.

Very Prolific and Produce Plenty of Seeds

R. cochinchinensis can produce more than 700 tillers and branches and can produce inflorescence. Perennial weeds can reproduce rapidly through vegetative means through tubers, rhizomes, and stolon. Scirpus maritimus, a perennial sedge, can produce more than 100 dormant and non-dormant tubers in one cropping season in irrigated rice paddies.

Ability to Survive and Adapt to Adverse Conditions

Weeds are capable of resisting drought and excessive moisture stress. Large crabgrass (Digitaria sanguinalis) form contractile roots and arrests its growth during extremely dry conditions and resumes their normal conditions until a favorable condition is met. The common purslane (Portulaca oleracea) incline their leaflets upward to reduce exposure to sun during dry conditions thus reducing excessive moisture loss due to transpiration.

Propagules Possess Dormancy or Can be Induced to Dormancy

Dormancy is a mechanism that enables the species to survive under unfavorable conditions. This mechanism is common to weed species and until a favorable condition for growth is observed.

Adapted to Crop Competition

Weeds have proper synchronized germination. They are able to germinate at the right time in favorable environments. Their seedlings are fast growing and can be rapidly established. Their quick response to moisture and nutrient availability make them well adapted to crop competition in the agroecosystem.

It is very important to know the characteristics of weeds so that proper and effective weed management measures can be design to solve weed issues. What even makes it difficult is that weeds are also plants, like the crop planted in the field, anything that can harm them can possibly harm the crop as well. The soil too is a seed bank of thousands of weeds so it is expected that a weed can grow in empty spaces in the agroecosystem. Weeds are also are important in disease development because some weed species are alternate hosts of some pathogens. Weeds also provide a niche for other insect pests in the field, hence, controlling them is a very important management practice in the field.

Weeds are also plants. The crops planted in the field are also plants so how can we differentiate a weed from a crop?

Weeds are found on land where the native vegetation has been replaced by a controlled system of cropping management. It is man who has forcibly altered the vegetation for other purposes mainly for agriculture. Crops, on the other hand, are plant that fit economically into the scheme of man’s work and existence. These plants are being managed to a certain degree. A plant species become a crop because man developed it to be a crop.

In the early days, weeds were not considered as pests in the field since: a) damage caused by weeds are not visible as those caused by insects and plant pathogens, b) crops are always associated with weeds, c) it is easier to see insects with crops than weeds, d) and there is seldom total crop failure due to weeds.

Damage of weeds to crops is not visible compared to insects that result to feeding trails and to diseases causing lesions and necrosis. When there is a crop, there is always a weed. That is why weeds were not considered as a threat to crop production. Sometimes, weeds look like crops so it is difficult to spot weeds in a heavily planted field. Unlike pests which are very noticeable in the field. Crop failure is less likely attributed to weed competition and there is seldom crop failure. These are some of the reasons why weeds were not regarded as pests before. At present, the direct and indirect contributions of weeds in crop failure have made it one of the pests considered in the field.

If you’re asking what are weeds, this article from Yami No Matsuei’s Hangout might help you.

Weeds are important component of the agroecosystem. They always grow with crops and its economic impact is greatest in agriculture. It is an important factor to consider in the management of land and water resources and dictate many of the crop production practices and management decision in growing crops.

We can defined a weed as a plant unwanted at a particular time and place and can do more harm than good under such time and place. The concept of a weed is man-made. One man’s crop may be another man’s weed. Of the 300,000 species of angiosperms, 10% 30,000 species behave as weed 99% of the time.

Weeds can be characterized to have a rapid vegetative growth, reproduce rapidly and mature early, be very prolific and produce plenty of seeds, have the ability to survive and adapt to adverse conditions, be adapted to crop competition, and whose propagules possess dormancy or can be induced to become dormant under favorable conditions.

The last characteristic of the weed is the reason why most of the empty lots we see today are populated with weeds. One year of planting would equal to seven years of weeding.

If you want to know how weeds are classified, you can read this article i got from Yami No Matsuei’s Hangout

Weeds are classified according to their similarities and differences which are effective in formulating an effective control program. These are according to their: a) Life Cycle, b) Gross Morphological Features, c) Body Texture, d) Habit-Manner of Growth, and e) Habitat.

According to their Life Cycle, weeds are classified as annual, or perennial. Annual weeds complete their life cycle in one season and reproduce mainly by seeds while perennial weeds live for more that one season and reproduce vegetatively and by seeds. They can either be simple perennials that reproduce only by seeds or creeping perennials that reproduce by seeds and by vegetative propagules.

Weeds are classified according to their Morphological Features can be grass, sedge, or broadleaf. Grasses have stems called culms that are cylindrical and has has a well defined nodes and internodes. Their leaves arise alternately in two rows. Ligules can be observed in grasses. Sedges on the other hand have triangular culms and does not have ligules. Their nodes and internodes are indistinct which are located at the basal part of the culm. Broadleaved weeds are characterized as having expanded leaves. They can either be monocots or dicots.

We classify weeds as herbaceous, woody, or vine according to the general appearance of their stems. Their habit of growth can be erect-those that have an upwight growth, prostrate-lying flat on the ground, or twining-those that are climbing or clinging for support.

Weeds can be aquatic-those living in water, terrestrial-grows on land, or aerial-or epiphytes growing in air or attached to trees or other support, according to their habitat.