Generally, an increase in one kg of weed growth will decrease one kg of crop growth. The weeds are undesired plants that intrude with man’s use of land or field and water in different ways.
The direct harmful effects of weeds may not be clear in many cases. Pests and causative agents (Pathogens) cause remarkable symptoms of infestation or infection. Weeds have harmful effects, also very slow rates, and such effects acquire almost at an irrevocable stage. The nature and amplitude of damage vary from one area to another area. The habitats may include, crop fields, non-crop fields, and aquatic environments for easy understanding. Weeds interrupt in various steads, they are discussed below:
Increase the Input Cost
As we know that tillage management comes to be near 10 % percent of the cost of crop cultivation and more than 50 % of the percentage cost applies to controlling weeds. The appearance of undesired plants makes it slow the progress of the crops in the field. There are some different processes, such that cultivation, harvesting, threshing, and cleaning. These processes take much time in the presence of weeds and thus increase the cost value.
Reduce the Production Value
The price of production in weed-infested areas or fields becomes cheap and reduces a lower price or cost. The field crop production combine or mixed with seeds and rubbishes of weeds poorly offered a low price. If the seeds of objectionable weeds/grains such production demoralize for sale. It means that the mix-up of weeds into the crop seeds also decreases the quality and price.
Reduce the Crop Yield
A crop field is a suitable environment where a large or different species of weed germinates in outbursts and grow profusely. If there is no limitation applies, they will battle with crop plants for nutrients, light, water, space, air, and other factors or agents in the ecosystem. The competition is more terrible under a stressful situation or position. As weeds are made up of a variety of plant types. They can adventure the environment more intensely than the field crop plants.
Moreover, Weeds do not affect the standing field crop but the crop in sequence and have an effect during the period of the non-cropped season. Weeds may produce a higher matter or mass than crop plants per unit area and always time. Some weeds compete for N, Pand K, and also some major and minor plant nutrients more than crop plants. Some parasitic weeds may kill the crop plants in drylands. Weeds consume the soil moisture and put the crop under water stress earlier. Thus, decrease the crop yield The yields reduction of individual crops varies from zero to a hundred percentage through various cropping systems.
Increase the irrigation requirements
Weeds pass the absorbed water by transpiration process, because as compare with field crops. The weeds absorb more water than crops. Thus increase the prevalence and bottom of application of water are very often costly and effortful or challenging to acquire. In the area of the field, weeds limit the movement of water and also decrease the efficiency of the supply of irrigation.
Reduce the quality and quantity of products from livestock and Birds.
There are some special weeds when eaten by milch animals which cause unwanted taste in their milk(like as Cleomeviscose, Paederia,foetida). There are some poisonous weeds by eating them, they cause serious disorders, permanent disability, and sometimes cause deaths. The weeds are such that Datura stramonium, the fruits, and seeds of weeds(such as Xanthium strumarium and Achyranthus aspera), twisted together with wool and hooks of Martynia annua can cause injury to suppress which fetch the price of the yield.
Harbor insects -pests (pathogens and parasites)
Some weeds protect the form of accommodation or the home of pests. They act as alternate hosts of a huge number of nematodes, viruses, fungi, and bacteria, etc. In the period of the off-season, these weeds harbor pests and during the session, they increase their reproduction. Weeds also provide food and home to the rats which spread in a troublesome manner to crop plants subsequently.
Reduce the value of land
some weeds cause a severe infection of perennial, sticky, and hairy adverse weeds. Thus, decrease the value of land as they require more expenditure to remove or eradicate from the land.
Cause allopathic effects
There are some weeds among the weeds (like Pzrtheninum hysterophorus) which release some toxic substances in the area that damage the germination and also the growth of crop plants, so the chemicals cause serious effects on the crop plant.
Cause health hazards to animals and men
Some different types of weeds cause allergy, irritation, and eczema to animals and workers when they come in touch with weeds or. such weeds are parthenium hysterophorus, Chenopodium album, Argemone Mexicana, and centipede minima cause serious problems such that wounds, headache, and vomiting.
How to control weeds
From the start of agriculture up to the middle of the 20 century, these weeds were used to control by plowing and hoeing directly. Nowadays two methods are common to control weeds i.e directly and indirectly. Directly Methods are those which aim to control the emergence, growth, and reproduction of weeds, which includes manual, mechanical, biological, and chemical methods of weed control. Indirect methods of weed control are those which do not use against specific species or weed flora. The indirect methods of weed control include, use clean seed, use clean field equipment, stop grazing of livestock, ensuring that the applied farmyard manure must be free from weed seeds, tillage practices, crop rotation, mulching, and last good farm management practices.
Conclusion
Weeds decrease crop yields or production by competing for nutrients such as water, space, gases, and light. Some weeds discharge or eliminate toxic substances, that hamper crop growth, and others may insects, diseases, or nematodes that attack crops. Weeds often cause problems during harvesting operations, and at times contamination with weed seeds or other crop plant parts may damage field crops unfit for market. Profitable crop production only depends on effective weed control. Effective weed control in field crops needs the use of a combination of different management techniques or methods, which including cultural methods and herbicides, Rotation of crops, and tillage practices to help reduce this problem.
Authors
Khair Ud Din
Waseem Ahmed
Asad Ullah Bugti