Chemical weed control

Chemical control is effective and herbicides being cheap, reliable, have facilitated a revolution in crop agronomy. Currently, herbicides share about two-third by volume of the pesticides used in agricultural production.
Globally herbicides constitute about 50-70% of total pesticides sale in USA and European countries like Germany, France and Austria. In India herbicides use comprises only 15-25% of total pesticide consumption and mainly used for irrigated wheat, paddy, soyabean, vegetables, tea, cotton, maize, sorghum and sugarcane.

What is herbicide?

  • Herbicides are chemical substances that kill or suppress plant growth by affecting one or more of the processes like cell division, tissue development, chlorophyll formation, photosynthesis, respiration, nitrogen metabolism and enzyme activities related to biosynthesis of proteins, fats and vitamins that are vital to plant survival.
  • Additives like powders, solvents, stickers or wetting agents are usually added to help disperse the active ingredient throughout a carrier. The final product is the formulated herbicide that may have number of names and may contain different proportions of active ingredient.

Time of application

  • Pre-plant applications are sprayed on the foliage of existing vegetation prior to planting or they are made to the soil and may be incorporated (mixed into the soil profile) in areas where rainfall is unpredictable or if the herbicide is volatile or is subject to rapid photo-decomposition.
  • plant applications may be made to (l) the soil surface following planting and prior to emergence of either crop or weeds (pre-emergence) or (2) to the weed and crop seedling whether in contact with the plant foliage or into the water (post-emergence). The movement of the herbicide during and following an application is an environmental concern that should always be addressed. Proper application procedures are essential to prevent symptoms or injury to adjacent crops as a result of herbicides drifting either in liquid or gaseous phase.

Methods of Herbicide Application

Herbicide applicators are for distributing an exact quantity of herbicide uniformly over an area.
  • Pressurized applicators – Hydraulic applicators (Knapsack sprayer)
  • Non-pressurized applicators – Granular applicator, Water gun, Direct contact applicator, Controlled–droplet applicators.
Nozzles Herbicides should not be applied like, insecticides and fungicides. Specific nozzles are used for herbicide spraying.
  • Flat fan nozzles: They produce a tapered edge, fan pattern for broadcast spraying and when foliar penetration and coverage are not required. The operating pressure should be low so that medium to coarse droplets.
  • Floodjet nozzles: Useful for liquids and mixture herbicides. They produce wide angle pattern and distribution pattern is not so uniform. Effective at low pressure in reducing drift.
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