Insect Pests of Vegetable, Ornamental and Spice Crops (2+1)

Pesticide residues

6) Pesticide residues:
Terminology:

• Deposit: The amount of pesticide initially laid down on the surface of the commodity is called as the deposit.
• Residue: pesticide residue means any specified substances in food, agricultural commodities, or animal feed resulting from the use of a pesticide. The term includes any derivative of a pesticide, such as conversion products, metabolites, reaction products, and impurities considered to be of toxicological significance. The term pesticide residue includes residues both from known as well as unknowns sources.
• Dissipation and persistence: In nature disappearance of residues takes place in two steps. The first step is initial phase in which the disappearance of residue is fast. This phase is called as dissipation. The second phase, in which there is slow decrease in the amount of residue, is known as persistence. The main difference in the two is that the dissipation follows the law of “first order kinetics”, whereas, the persistence does not follow this law.
• Residue half life (RL50): It is the time in which half of the amount of the initial deposit is eliminated by reaction or dissipation.
• Maximum residue limit (MRL) or tolerance: It is the maximum concentration (in ppm) of pesticide residue that is permitted in or on food at a specified stage of harvesting, transport, marketing or preparation of food up to the final point of consumption.
• Acceptable daily intake (ADI): It is the daily intake, which during an entire lifetime, appears to have no appreciable risk to the health of the consumer on the bases of all the known facts at the time of the evaluation of the chemical. It is expressed in mg of chemical per Kg body weight. ADIs are derived on the bases of long term feeding studies with laboratory animals. A safety factor of 100 is applied to express the non observed adverse effect level in the most sensitive animal studied.
• Waiting period: It is the time interval (days) between final spray and harvest of the crop. It is the time which is required for initial deposits to dissipate below MRL.
• LD50: It is the dose of a chemical express in mg/ Kg required to kill 50% of the test organisms. It is also called as median lethal dose.

• Only a small amount (less than 1%) of pesticide applied on a crop reaches the target pests
• More than 99% enters the environment
• Major source of human exposure to these pesticides is food, however, drinking water, inhalation and dermal contacts also leads to residues in humans.
• Due to the ban of pesticides like DDT, HCH, aldrin, dieldrin heptachlor, etc. a decline in the pesticide residues has been observed in recent past
• Ways and means to minimize pesticide residues:
• Observe IPM strategies and pesticide should be used only when it absolutely essential (as last alternative)
• Always use approved pesticides at recommended doses and at appropriate time. Avoid indiscriminate and unwarranted use of pesticides in pest management programmes.
• Preference should be given to less persistence pesticides and never use banned or restricted pesticides
• Monitor the crop regularly for pest incidence and use pesticides only when it reaches ETL
• Use selective, ecofriendly and less persistence pesticides
• Ripe fruits and vegetables should be plucked before pesticide application and after pesticide application the crop should be harvested only after observing recommended waiting period.
• Pesticide residues on food commodities can be reduced by processing like washing, peeling and cooking.
• Farmers should develop a habit to read and follow the instructions given on pesticide container/ leaflet which are use full in using the pesticide effectively and safely.
• Farmers should develop a habit to maintain spray diary containing time of application, dose and type of pesticide applied.

MRL values of some common insecticides on some vegetables

Insecticide	Commodity	MRL (mg/Kg)
Carbaryl	Okra and leafy vegetables Other vegetables	10 5
Diazinon	Vegetables	0.5
Dichlorvos	Vegetables	0.15
Dicofol	Fruits and Vegetables Chillies	5.0 1.0
Dimethoate	Fruits and Vegetables Chillies	2.0 0.5
Endosulfan	Fruits and Vegetables Chillies	2.0 1.0
Malathion	Vegetables	3.0
Lindane	Fruits and Vegetables	1.0
Methyl parathion	Vegetables	1.0
Chlorfenvinphos	Vegetables	0.05
Chlorpyriphos	Potato and onion Cauliflower and cabbage Other vegetables	0.01 0.01 0.2
Ethion	Cucumber and squash	0.2
Formathion	Vegetables Peppers and tomato	2.0 1.0
Phosalon	Potato Other vegetables	0.1 1.0
Trichlorfon	Fruits and Vegetables	0.1
Thiometon	Potato Other vegetables	0.05 2.5
Carbofuran	Fruits and Vegetables	0.1
Cypermethrin	Egg plant Cabbage Okra	0.2 2.0 0.2
Fenvalerate	Cauliflower Egg plant Okra	2.0 2.0 2.0
Phorate	Tomato Other vegetables	0.1 0.05
Permethrin	Cucumber Soybean	0.5 0.5
Quinalphos	Cardamom	0.01
Triazophos	Chillies	0.2
Fenpyroximate	Vegetables	0.02
Spiromesifen	Tomato Cucurbits	0.45 0.1
Dicofol	Fruits and Vegetables	5.0 (PFA)