How to prevent the weeds growing in the garden ?

Weeds are ubiquitous. They grow everywhere, compete with crops for soil moisture, nutrients, solar radiation, and space, thus reducing the crop yields. Weeds also act as alternative hosts that harbor insects, pests and diseases, and micro-organisms. Some weeds release into the soil inhibitors or poisonous substances that may be harmful to the crop plants and livestock. In the aquatic environment, weeds block the flow of water in canals, water-transport system, and drainage system, rendering navigation difficult. The dense growth of aquatic weeds pollutes water by deoxygenating it and killing the fishes. Weed management is done through mechanical, chemical, and biologically.

Crop losses due to weeds:

Most of these weeds are self-sown and they provide competition by virtue of 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. Besides competition for resources, weeds often reduce crop growth and yield by the release of allelochemicals into the environment.

Crop-weed competition:

Weeds compete with crop plants for nutrients, moisture, and light. The degree of competition is dependent on weed flora, time of weed emergence, a relative density of crop plants and weeds, the duration of the competition, management practices..etc. When the crop seeds are planted weed seeds also germinate along with them. During the initial stages, both crop plants and weeds grow without competing with each other. However, as the plants grow bigger and bigger, they compete with each other for the resources and the one which is stronger numerically, morphological, physiologically and biochemically will benefit more at the cost of the other. 

       The stage at which there is the maximum impact of weeds on crop growth is termed as a critical period of weed competition, which usually varies between 15 and 60 days after sowing depending upon the crop, crop duration, time of weed emergence, weed flora and soil and climatic conditions. There will be least or no damage done by the weeds, once the crop is established and the canopy covers the ground. 

How to prevent the weed from growing in your garden?

   In order to reduce the negative implications of weeds on crop growth and yield, weeds have to be controlled efficiently. Prevention, Control, and eradication are the key elements in weed management.

Prevention:  

          Involves procedures that inhibit or delay weed establishment in areas that are not already inhabited by them. These practices restrict the introduction, propagation and spread of weeds on a local or a regional level. Preventive measures include cultural practices such as seed cleaning, use of the weed-free seed, manure, and machinery, controlling weeds on field bunds and irrigation canals, screening irrigation water, etc. 

Eradication: Total elimination of a weed species from a field or a region. It requires the complete removal of seed and vegetative parts of a weed species in a defined area. Soil sterilant is done particularly in nurseries for eliminating soil pathogens and pests including weeds.

There are few general methods of weed control are listed below,

Physical methods: Hand - weeding with the help of hand chisel, hand hoe, spades, hoeing, tillage, mowing, burning, flooding, smothering..etc are examples of physical methods of weed management, involving the use of physical energy through implements either manually or bullock drawn or power operated.

Cultural practices: 

          Weed species are better competitors than crop plants for light, water, nutrients, and space. However, cropping practices can be intelligently used to shift the competition in favor of crop plants. Quality seeds with good germination will give the crop a vigorous and close stand. Varieties well adapted to a season will compete better. Crop plants with larger leaf areas and good branching will compete better than weeds. 

           Crops like Sudan grass, sorghum, and cowpea are good competitors, where such as linseed, groundnut, and lentils are poor competitors. Close row crops compete better with the weeds than wide-row crops. Crop rotations are required to minimize the dominance of a particular weed in the cropping system. Inter-cropping, fast-growing crops such as cowpea, soybean ..etc in wide-spaced crops like maize, pigeon pea, or sugarcane would reduce weed competition. Also covering inter-row spaces with mulches(plant residues, paper, plastic) also contain weed growth.

Biological method to prevent the weeds from growing in the garden: 

         In this method, the natural enemy of a weed plant is used to control the weed. An outstanding example is that of prickly pear( Opuntia spp) in Australia. And another example is the destruction of Lantana with the help of Telonemia scruples. Water hyacinth can also be controlled through the use of Neochetina bruchi and N.eichhorniae. Successful control of Parthenium hysterophorus has been reported with the help of Mexican beetle Zygogramma bicolorata. The eradication of prickly pear by using the cochineal insect ( Dactylopius tomentosus) in Tamilnadu and Maharashtra is the best example of biological control in India. The destruction of aquatic vegetation in ditches by using herbivores fish such as Chinese grass crap Ctenopharyngdon idella. Besides controlling submerged aquatic weeds, the fishes could be a valuable source of nutritious food for human consumption. The use of geese to control weeds in cotton is popular in some areas in South-west America.