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Crops weed

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  • Penn State Extension – Introduction to Weeds: What Are Weeds and Why Do We Care?
  • eOrganic – An Ecological Understanding of Weeds

Weed, general term for any plant growing where it is not wanted. Ever since humans first attempted the cultivation of plants, they have had to fight the invasion by weeds into areas chosen for crops. Some unwanted plants later were found to have virtues not originally suspected and so were removed from the category of weeds and taken under cultivation. Other cultivated plants, when transplanted to new climates, escaped cultivation and became weeds or invasive species. The category of weeds thus is ever changing, and the term is a relative one.

Weeds interfere with a variety of human activities, and many methods have been developed to suppress or eliminate them. These methods vary with the nature of the weed itself, the means at hand for disposal, and the relation of the method to the environment. Usually for financial and ecological reasons, methods used on a golf course or a public park cannot be applied on rangeland or in the forest. Herbicide chemicals sprayed on a roadside to eliminate unsightly weeds that constitute a fire or traffic hazard are not proper for use on cropland. Mulching, which is used to suppress weeds in a home garden, is not feasible on large farms. Weed control, in any event, has become a highly specialized activity. Universities and agricultural colleges teach courses in weed control, and industry provides the necessary technology. In agriculture, weed control is essential for maintaining high levels of crop production.

The many reasons for controlling weeds become more complex with the increasing development of technology. Plants become weeds as a function of time and place. Tall weeds on roadsides presumably were not problematic prior to the invention of the automobile. However, with cars and increasing numbers of drivers on roads, tall weeds became dangerous, potentially obscuring drivers’ visibility, particularly at intersections. Sharp-edged grasses are nominal nuisances in a cow pasture; when the area is converted to a golf course or a public park, they become an actual nuisance. Poison oak (Toxicodendron diversilobum) is rather a pleasant shrub on a sunny hillside in the open country; in a camp ground it is a definite health hazard. Such examples could be given ad infinitum to cover every aspect of agriculture, forestry, highway, waterway and public land management, arboretum, park and golf-course care, and home landscape maintenance.

Weeds compete with crop plants for water, light, and nutrients. Weeds of rangelands and pastures may be unpalatable to animals, or even poisonous; they may cause injuries, as with lodging of foxtails (Alopecurus species) in horses’ mouths; they may lower values of animal products, as in the cases of cockleburs (Xanthium species) in wool; they may add to the burden of animal care, as when horses graze in sticky tarweeds (Madia species). Many weeds are hosts of plant disease organisms. Examples are prickly lettuce (Lactuca scariola) and sow thistle (Sonchus species) that serve as hosts for downy mildew; wild mustards (Brassica species) that host clubroot of cabbage; and saltbrush (Atriplex species) and Russian thistle, in which curly top virus overwinters, to be carried to sugar beets by leafhoppers. Many weeds are hosts of insect pests, and a number are invasive species.

Modern weed control can be classified as mechanical, chemical, or biological.

Mechanical control

Mechanical weed control began when humans first pulled weeds from their cereal crops and attempted to grow single plant species, free from all plant competition. That was the start of monoculture, a method that since has come to dominate agriculture. Contrary to the principles of ecology, farmers throughout the world grow the major food, fibre, and forage crops in a monoculture because experience has shown that the highly improved modern crop species give their highest yield under this system.

From hand pulling, humans devised simple tools such as the spud, the knife, and the hoe to eliminate weeds. For thousands of years, from the Egyptian culture to the Renaissance, those simple methods were used. The first efforts to turn away from simple hand methods and mechanize the arduous task of weed control began in 17th-century England. Since then there has been continuous improvement of agricultural tools used to destroy weeds and of cultural methods employed to minimize weed growth. The principal virtue of cultivation of row crops is the control of weeds. Any method of weed control that minimizes tillage tends to conserve soil structure and maintain fertility.

In addition to tillage, other mechanical methods of weed control involve burning, grazing, and the use of ducks or geese in certain crops (in cotton and mint especially). All of those methods have drawbacks: there is the arduous, painful nature of hand weeding; the repetitious and often harmful nature of clean tillage with machinery; the slow, fuel-consuming nature of burning; and the costly requirement of livestock or fowl for the biological grazing methods. Tillage, still the most widely used method of row-crop weed control, has been greatly improved by development of precision seeding and close preadjustment of tiller tools, allowing the passage of weed knives within an inch or less of the young crop plants. Despite these improvements it is known that weed knives injure crop roots, especially late in the tillage season. Additionally, tillage tools can spread perennial weeds rapidly, bringing about rapid infestation of whole fields.

Such methods as crop rotation, use of smother crops, use of weedfree seed, mulching and covering, and cleaning of machinery to prevent spread of weed seeds are also classified as mechanical.

Weed, general term for any plant growing where it is not wanted. Weeds interfere with a variety of human activities, and many methods have been developed to suppress or eliminate weeds. In agriculture, weed control is essential for maintaining high levels of crop production.

what is a crop vs. weeds in agriculture: a perspective

What is a crop? What are crops? What are weeds? These are elementary questions and for those who have undertaken formal study of the basics of agriculture, they may seem to be unnecessasary questions. Are they?

Nonetheless, for the beginners at least, it is important to be clarified on the terms. The clarification becomes more relevant in view of the increasing concerns on the environment and biodiversity conservation. It is in connection with these concerns that cutting of trees has become an issue of absolute right or wrong.

Various dictionaries will show that the word “crop” has multiple meaning. Some of these are completely different from the other so that one who is familiar with the use of the word in one instance may be confused when the same word is used differently. For example, the word can refer to a harvested produce such as grains, fruits, etc. It is also common in computerized trimming of photographic images.

In agriculture, the terms crops and weeds have already been attached to many plant species without qualification. Corn (maize), sugarcane, coconut, etc. are automatically listed as agricultural crops because they are always grown intentionally for some purpose. Their economic importance are already established. Conversely, many plants are listed as weeds (e.g. cogon or Imperata cylindrica , aguingay or Rottboellia exaltata , purple nutsedge or Cyperus rotundus , etc.) because they always grow unintentionally and hamper with or cause adverse effects on the growth of crops. But there are much more about these terms.

What is a Crop: Useful vs. Unuseful Plants

This paper refers to the crop (pl. crops) which is short for agricultural crop. It is a term which is commonly defined in the simplest way as a plant which is useful to man. It can be an agronomic crop , a horticultural crop or agroforest crop, or classified further under more specific grouping such as food crops, non-food crops, cereals , grain legumes or pulses , etc.

In contrast, a weed is a plant which is unuseful or a plant which grows where it is not wanted. The main distinction, therefore, between crops and weeds in agriculture is that crops are useful while the contrary applies to weeds.

Nicely and easily stated. But not quite clear. To better understand what is a crop and what is a weed, it is essential that the words “useful” and “unuseful” be clarified. It is therefore necessary to delve first on the question “Are there plants which are not useful to man?” The answer should be No. All plants are useful to man. If not directly, then indirectly.

With rare exception, plants photosynthesize in which process the energy from the sun is converted to chemical energy and trapped in organic compounds. This chemical energy from plant-based food is utilized by man and other heterotrophic organisms to fuel their life processes.

Photosynthesis in plants also generates oxygen which is essentially needed in aerobic respiration. In addition, the carbon component of the absorbed CO2 is used as structural bases in building organic, or carbon-containing, compounds including complex carbohydrates, proteins, fats and oil. Upon decomposition, all plants also enrich the soil or contribute to soil-making.

So why is it that the description “useful” is equated with what is a crop? If all plants are useful, then all plants should be crops and none will qualify as weeds. Consequently, there would be no need to invent the term weed in agriculture. But both terms exist and are continually used.

Again, what is a crop?

Crop and Weed Further Distinguished

It is likewise important to be able to distinguish what is a crop from weed. To reemphasize, the term crop refers to agricultural crop, a plant which is useful to man and thus grown intentionally or otherwise taken care of. It means that said plant has a use or uses to a person or group of persons as a source of food or feed, cash, or some other obvious benefits, including its usage in ornamental horticulture and for special purposes such as shade crop, cover crop, green manure, windbreak, erosion control, etc. Thousands of uses can be enumerated.

But there are no hard rules on which particular uses apply to a specific plant. It depends on the needs of particular persons, subject to certain time-specific plans and purposes. Another consideration is the inherent characteristics of plants. Some plants yield abundant fruits, while others produce seeds, modified roots and stems, leaves, flowers, fiber, oil, etc. with commercial demand. For a subsistence farmer, the potential of a plant to supply food and basic needs to the family is the main consideration in growing it or in preserving and managing a naturally growing plant.

Further enlightenment on what is a crop should likewise be extended to the concept of weeds. Weeds have been defined as plants which are unuseful . The concept of weeds could possibly have started with the ancient man when he begun to domesticate plants. He had to remove the nearby plants, including vines, which interferes with the growth of and access to selected plants which grow in the wild.

However, the application of the word “unuseful” or “useless” or “not useful” to weeds is somewhat confusing because, as earlier noted, no plants are absolutely useless. Also, it doesn’t much help in clarifying what is a crop because these words (unuseful, useless and not useful) are mere antonyms of “useful”. A modified definition is more enlightening and descriptive of the change in the concept of a weed: A weed is a plant which grows where it is unwanted. Stated another way, it grows on a particular spot in which it is not wanted or not needed.

This definition of weed eliminated the misleading connotation from the use of the word unuseful or useless that some plants are indeed without any use. It means that any live plant can be a weed depending on where it grows. It does not matter whether it is an annual, biennial or perennial, or it belongs to any botanical or crop classification, or a seedling or adult, or a native species or introduced.

The basis of a weed is its location in respect to some other plants (the crop) which grow or are intended to be grown for some use or useful products. If it is there where it is unwanted or not needed, or it hampers with the growth of a crop, then it is a weed. The same effect occurs when a plant prevents movement or passage or any farming operation within the farm. Likewise, some introduced plant species have become causes for concern because of their damaging effect on biodiversity. These include the neem tree ( Azadirachta indica) which has been identified as an invasive alien species (IAS).

Interchangeability of the Terms

For more clarity on what is a crop, it should be apparent also that any crop, although already established as an economically important plant, may not always remain a crop. Any crop can become a weed. Corn is one of the major crops in the world, but when it grows unintentionally in a plot which is intended solely for a certain vegetable then it (the corn) becomes a weed. Trees provide shade and other benefits, but when they cause inhibitory effects on fruit crops in the orchard or on forage crops in the pasture then they become weeds.

Some plants or trees can even become weeds within the same species. When plants are closely spaced, thinning or the removal of excess plants is usually the final resort.

Conversely, a weed may become a crop. Some examples: In some localities, the cogon grass (Imperata cylindrica) has been managed and harvested for roofing; grass weeds have been utilized as source of forage for grazing animals and an ingredient in vermicomposting ; and some weeds have been retained intentionally and used as herbal medicine (e.g. ringworm bush, sunting or Cassia alata) or as source of vegetable (e.g. jute, saluyot or Corchorus olitorius and amaranth, kulitis or Amaranthus spinosus).

The concept of a weed is similar to that of nuisance. When something becomes a nuisance, a person affected will likely cause its abatement (or removal). Similarly in crop production, clearing, weeding, and thinning are standard operations.

Disclaimer: This elaboration on what is a crop should not be interpreted as promoting the indescriminate cutting of trees. The author himself has actively participated in the production of planting materials and in the growing of fruit trees and bamboo. Rather, exacting decisions are anchored upon correct information.

An elaboration on what is a crop vs. weeds in agriculture. The definitions of crop and weed are discussed.