• What are "weeds" ?

• « adventice » means « which comes from outside » in latin, in other words, it indicates an introduced plant. However, the adventice is rather considered as a « plant that develops spontaneously in environments modified by man». The difference is infinitesimal since most adventices are introduced plants.
• The term « weeds » has a weed science meaning since it indicates an « unwanted plant ». This definition being vague, it is proper to consider that the plant called weed as one which has grown somewhere after the setting up of a human activity and that it became harmful to that activity directly or indirectly.

Likewise, all the plants we call « weeds» are not necessarily harmful. They become so as from an infestation threshold since a plant can’t de considered bad if it doesn’t harm the crop among which it grows. When a species is present without creating a competition with the crop and without being harmful, we talk of a minor species.

When the species hampers the development of the crop through chemical and biological interactions, (direct harmfulness) or alters the quality of the harvest or makes harvest more difficult increases the work’s hardness (indirect harmfulness), it is considered as a major species. These plants have generally become invasive or embarrassing in developing a certain number of adaptations of its reproduction (number of seeds, pollination mode, …) and their physiology (growth, competitiveness, …). On the other hand, there are certain adventice plants that can be useful to man (as food crops, medicinal herbs, textile, …) or for cultivation (improvement of the soil’s structure, contribution in organic elements, …)

The general term " weeds ", used in France to indicate plant species growing in cultivated plots without having been intentionally planted is definitely not adequate, but the French language doesn’t have any other alternative yet. Broadly speaking, it can be used to indicate all the species belonging to the flora of cultivated plots, without prejudging of their action on the crop since weeds are defined by some people as plants of which the utility has not been found yet.

The term "mauvaise herbe" or "weed" in English will then be used for any plant being in a place where it has not been desired and where it has a negative economical or environmental effect.

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