Characteristics of weeds

 Characteristics of weeds 

Weeds are also like other plants but have unique characteristics that tend to put them in the  

classification of unwanted plants.  

• Most weeds especially annuals produce an enormous quantity of seeds, e.g. wild  

oats (Avena fatua), which have a million roots. It has been observed that among 61 perennial  

weeds, the average seed-production capacity was 26,500 per plant.  

• Weeds can resist adverse conditions in the field because they can  

modify their seed production and growth according to the availability of moisture and  

temperature. They can germinate under unfavorable soil-moisture conditions, have a short  

span of plant growth, naturally grow faster rate and produce seeds earlier than most of  

the crops growing in the association.

Weed seeds remain viable for longer periods without losing their viability, e.g. annual  

meadow grass (Poa annua) and scarlet pimpernel (Anagallis arvensis) remain viable for  

about 8 years; creeping thistle (Cirsium arvense) for 20 years and field bindweed  

(Convolvulus arvensis) for about 50 years.  

• Weed seeds have a tremendous capacity to disperse from one place to another through  

wind, water, and animals including man. Many times, weed seeds mimic the crop  

seeds due to their size and get transported from one place to another along with them.  

Harmful effects 

• Weeds have serious impacts on agricultural production. It is estimated that weeds generally cause a 5% loss in agricultural production in most developed countries, a 10% loss  

in less developed nations, and a 25% loss in the least developed countries. 

In India, yield losses due to weeds are more than those from pests and diseases.  

Yield losses due to weeds vary with the crops. Every crop is exposed to severe  

contest from weeds. Most of these weeds are self-sown and provide  

competition caused by their faster growth rate in the initial stages of crop growth. In  

some crops, the yields are reduced by more than 50% due to weed infestation.   

Weed seeds stay viable for longer periods without losing their viability, e.g. annual  

meadow grass (Poa annua) and scarlet pimpernel (Anagallis arvensis) remain viable for  

about 8 years; creeping thistle (Cirsium arvense) for 20 years and field bindweed  

(Convolvulus arvensis) for about 50 years.  

• Weed seeds have a tremendous capacity to disperse from one place to another through  

wind, water, and animals including man. Many times, weed seeds mimic the crop  

seeds due to their size and get ferried from one place to another along with them.  

Harmful effects 

• Weeds have serious impacts on agricultural production. It is estimated that weeds generally cause a 5% loss in agricultural production in most developed countries, a 10% loss  

in less developed countries, and a 25% loss in the least developed countries. 

In India, yield losses due to weeds are more than those from pests and diseases.  

Yield losses due to weeds vary with the crops. Every crop is exposed to severe  

competition from weeds. Most of these weeds are self-sown and provide  

contest caused by their faster growth rate in the initial stages of crop growth. In  

some crops, the yields are reduced by more than 50% due to weed infestation.   

Weeds reduce the quality of marketable agricultural produce. Contamination of weed  

seeds of Datura, Argemone, Brassica, etc., is harmful to human health and weed seeds  

present in the produce cause odd odour sometimes. 

• Weeds not only reduce yield but also interfere with agricultural operations. Weeds make  

mechanical sowing a difficult process and render harvesting difficult, leading to  

increased expenditure on labor, equipment, and chemicals for their removal.  

• In aquatic environments, weeds block the flow of water in canals, water-transport systems, and drainage systems, rendering navigation difficult. The dense growth of aquatic weeds  

pollutes water by deoxygenating it and killing the fish.  

• Weeds are also a nuisance and a fire hazard along railway lines, roads, right-of-ways,  

airports, forests, and industrial sites.  

Some weeds release into the soil inhibitors of poisonous substances that may be  

harmful to crop plants, human beings, and livestock. Health problems caused by  

weeds to humans,

Beneficial Effects-

 

Despite all the difficulties caused by weeds, they can offer some beneficial properties,  

mainly when occurring at low densities. These aspects should be utilized in the farming  

system, although this may make organic management more complicated than chemical-based  

systems. Some of the potential benefits of weeds are listed below: 

• Helping to conserve soil moisture and prevent erosion. A ground cover of weeds will  

reduce the amount of bare soil exposed helping to conserve nutrients, particularly  

nitrogen which could otherwise be leached away, especially on light soils.  

• Food and shelter can be provided for natural enemies of pests and even alternative food  

sources for crop pests. The actual presence of weed cover may be a factor in increasing  

the effectiveness of biological control of pests and reducing pest damage.  

• Weeds can also be valuable indicators of growing conditions in a field, for example,   

water levels, compaction, and pH. 

• Weeds can be an important source of food for wildlife, especially birds. Bird populations  

have been declining on farmland over the last few decades and leaving weeds as a  

resource has been shown to help revive bird populations.