Mechanical or Physical Methods of Weed Control
This includes the use of hand tools, implements and machinery operated either with the help of man power, or machine power for control of weeds. These are the costly and time consuming methods. However, these methods cause minimum damage to the environment.
i) Hand Pulling or Hand Weeding:
Pulling the weeds by hand or hand weeding with the help of weeding hook is the oldest and most effective methods for control of weeds. Weeds can be easily uprooted after a good soaking irrigation or rain. Weeding should be done before flowering stage of weeds for avoiding seedling and further spread of weeds. Because as per the old saying. One year’s seeding is seven years weeding. This is costly and time consuming method.
It is one of the practical method of destroying weeds of all categories.
a) Deep Ploughing:
Weeds are buried deep in the soil and also exposed to heat of the sun by deep ploughing. Many annual and perennial weeds can be controlled by deep ploughing and exposing the field to heat of the sun.
Helpful for cutting and burying of weeds. Harrowing with blade harrow is very effective for destroying newly germinated weeds before sowing of the crop.
Interculturing with different types of hoes or mechanical weeders is useful to control weeds in between rows of the crop.
iii) Mowing and Sickling:
This method is used lands, pastures, gardens and roadsides. The implement mower is use for cutting weeds. It does not destroy the weeds completely but prevents seed production by cutting growing parts. Cutting above ground parts of weed with sickle is called sickling and it prevents seed information.
It helps in controlling weeds like kans. ( Saccharum spontaneum) which grows luxuriantly in heavy ill drained soils during rainy seasons. The fields are embanked with tall bunds to impound water. The weeds get submerged under water and are smothered.
This method is adopted to destroy weeds in non-cropped areas like waste lands road sides, railway lines, bunds etc. The flame throwers and steam boxes are used for burning weeds in advanced countries. The flame should be so adjusted that is causes only wilting but not charring of weeds. Heat kills the living cells by coagulating the protoplasm and inactivating enzymes. The thermal death point (TDP) of most plant cells lies between 45 to 55 o c (113 to 131 0 F). Rabbing in Konkan area is widely practiced to kill weeds seeds particularly from paddy nursery areas. It is not a good method, since the useful vegetation and organic matter is also destroyed along with weeds.
This method is useful for controlling perennial weeds like nut grass, hariali etc. Digging is very useful for removing the under ground propagation parts of weeds form the deeper layer of soil digging , hand collection and destruction of under ground parts of weeds is adopted when noxious weeds are observed in the patches in the field. It is not economical on large areas as it is costly and time consuming method.
The principle aim of this method is to cut off light and avoid all top growth of weeds. The organic mulches such as plant residues i.e Stubbles, wheat straw , rice hulls, sugarcane trash etc are spread in between crop rows @ 5 tonnes/ha and thickness about 10 to 15 cm. The inorganic mulches such as black or white polythene sheet is spread in between crop rows. However, it is expensive and used for high value crops only. The black polythene is more effective for controlling weeds.
viii) Summer Fallow:
This method is widely practised in dry farming areas. The land is ploughed after harvest of rabi crop and left without any crop in summer season. The underground parts of the perennial weeds are exposed to strong sunlight and destroyed.
ix) Dredging and Chaining:
These methods are useful for controlling aquatic weeds. Removing of weeds along with their roots and rhizomes from the water with the help of mechanical force is called dredging. The floating aquatic weeds are removed by changing. A heavy chain in pulled over the water bodies to collect the weeds.
The combination of mechanical and cultural methods is effective for minimizing the weed population.