Use of adjuvants with herbicides to minimize environmental risk

Now a day environmental protection is one of the main prospective of scientists research. Different human activities are cause of polluted environment in which “chemicals use” is most important. In agriculture sector chemicals are being used on large scale than any other sector in the form of fertilizer, herbicides, insecticides and pesticides. Every year million tons of chemicals are used to increase the productivity of crops for meeting the requirement of increasing population around the globe. Chemicals are necessary to enhance the production but their indiscriminate use is source of water, air and soil pollution.

Herbicides have significant effect on environmental pollution as these consist of different poisoning chemicals. These can suppress the weeds, which can reduce yield upto 70% depending upon their intensity. Farmers are eager to achieve maximum yield of crops, so they use higher doses of herbicides to suppress the weeds. Improper use of herbicides pollutes the underground and nearby water body be leaching of chemicals, air pollution by volatilization of chemicals and soil pollution by longer persistent periods.

Although herbicide use is quick and efficient method to control weeds but it has detrimental effects on environment. It is need of time to conserve environment by reducing use of herbicides but we cannot compensate the yield loses on the other hand. So, scientists are working to solve this problem in which we may reduce use of herbicides without compromising the yield of crops.

Emerging trend in this regard is use of “adjuvants”. An Adjuvant is any compound which is added to herbicide formulation or tank mixture to enhance the efficacy of herbicides. In this way we can reduce the herbicide doses by 25% which can decrease the environment pollution as well as it will be economical for farmers. Adjuvants are easily available in market at cheaper price. These enhance the efficiency of herbicides by creating easiness in application, higher persistent period on weeds leaves, easiness in penetration in weeds and reducing loss of herbicides from leaching, volatilization and chemical ineffective bonding.

Adjuvants are classified in different types which are following with their action.

Surfactant: The name is derived from surface active agents. Surfactants are the most widely used and probably the most important of all adjuvants. The primary purpose of a surfactant is to reduce the surface tension of the spray solution to allow more intimate contact between the spray droplet and the plant surface. Water has a surface tension of 73 dynes/cm. Surfactants lower the surface tension of water to that of an oil or solvent, which spreads more readily than water on plant surfaces. Surfactants typically lower the surface tension of a solution to between 30 and 50 dynes/cm. These facilitate or enhance the emulsifying, dispersing, spreading, sticking or wetting properties of the herbicide tank mix. Surfactants work by improving contact between spray droplets and plant surfaces, and enhance absorption by:

1. Making the spray solution spread more uniformly on the plant

2. Increasing retention (or sticking) of spray droplets on the plant

3. Increasing penetration through hairs, scales, or other leaf surface structures

4. Preventing crystallization of spray deposits

5. Slowing drying and increasing water retention in the spray droplets

Oil Adjuvants: Oil adjuvants can increase the penetration of oil soluble herbicides into plants and are commonly used when conditions are hot and dry or when leaf cuticles are thick. They are derived from either refined petroleum (mineral) oils or from vegetable oils (including seed oils) and do not readily mix with water. Therefore, when an oil adjuvant is combined with water in a spray tank, a surfactant emulsifier must also be added, which distributes the oil droplets uniformly throughout the mix. These emulsifiable oil adjuvant combinations typically contain both non phytotoxic oil typically ranging 80 to 99% and a surfactant 1 to 20%, and are added to the spray tank usually as just 1% of the total spray volume.

Ammonium Fertilizers: Ammonium fertilizers are often added to herbicide mixes in range and row crops where the addition of fertilizer works to both enhance herbicidal effects as well as to stimulate the growth of desirable crop or forage plants. Ammonium fertilizers can function as utility adjuvants because they help prevent the formation of precipitates in the tank mix or on the leaf surface. They also decrease surface tension, increase spreading of the herbicide on the leaf surface, neutralize ionic charges, and increase herbicide penetration into the leaf. Ammonium fertilizers are used primarily with broad leaf specific herbicides.

Dyes, foaming agents, thickening agents, Deposition agents, water conditioners, pH buffers and humectants can also be used as adjuvants. If we want to reduce environmental pollution by reducing the use of herbicides without compromising the yield of crops, we should promote this approach on large scale among farmer community as it is economical and efficient method to control weeds with herbicides.

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