Pesticide is a ‘generic’ term given to any chemical used to control a pest or disease. Pesticides contain an active ingredient and a wetting agent. Types of pesticide include acaricides (to kill mites), fungicides (fungals), bactericides (bacteria), herbicides (weeds), insecticides (insects), miticides (mites), molluscicides (snails and slugs), nematicides (eelworms), rodenticides (kill rats and mice). Desiccants, defoliants, fumigants, insect-repellants, insect-attractants and plant-growth regulators are all also considered pesticides.

CONTACT OR SYSTEMIC: Contact sprays are those that are sprayed on to the crop, remain on the surface and kill on contact. Systemic are those that enter the plant or organism and remain in the tissues.

PERSISTENT OR NON-PERSISTENT / Persistent are those that are stable, do not biodegrade easily, and persist in the environment – and remain active – for anything from a few months to several years. Non-Persistant pesticides biodegrade and quickly become inactivate.

ACTIVE & INERT COMPONENTS / A pesticide product has two main components: the active ingredient(s) and the inert (other) ingredient(s). The active ingredient is the specific compound designed to adversely effect a pest. Pesticide active ingredients are generally not applied in their pure form, but are usually included in formulations with inert ingredients that improve their storage, handling, application, effectiveness, or safety. While the term “inert” implies that a substance is non-toxic, many inert pesticide ingredients are toxic to some degree. Assessments of the toxicity of pesticide products must therefore consider both active and inert ingredients. Inert ingredients must usually be approved by government authorities and may be classified into several toxicity categories. However, data identifying the specific inert ingredients in all registered pesticide products is not always publicly available.

MRL & ADI / Maximum Residue Levels (MRL) and Acceptable Daily Intake (ADI), expressed in milligrams per kilogram (ml/kg), are the terms quoted whenever pesticides are discussed (Brown, L: 1998). These definitions are taken from governmental WPPR (Working Party on Pesticide Residues) reports. (Source: Lynda Brown, 1998).

MAXIMUM RESIDUE LEVEL (MRL) / The maximum concentration of a pesticide residue legally permitted in or on food commodities and animal feeds. It is expressed in milligrams per kilogram (ml/kg). Based on Good Agricultural Practice (GAP) data, it represents the maximum residue permissible when a pesticide has been applied in the correct dose and at the correct rate, in or on food when it leaves the farm gate. MRLs are thus the legal standard against which residues in food are measured. Though MRL is the figure usually referred to, it is not a safety standard and has nothing to do with health,” (abridged from Brown, L: 1998).

ACCEPTABLE DAILY INTAKE (ADI) / The amount of a chemical that can be consumed every day of an individual’s life in the practical certainty, on a basis of all known facts, that no harm will result, expressed as milligrams per kilogram of body weight (mg/kg). This is a safety standard, with very wide built-in safety margins, set at one hundred times less than the No Effect Level (NEL). Note: MRL figures are set well below ADI figures. In practice, pesticide residues exceeding MRLs are common; those exceeding ADIs are very rare. (Source: Lynda Brown, 1998).

TOXICITY / The toxicity of a pesticide is expressed by the terms oral and dermal LD. LD50 means the minimum single dosage needed to kill 50% of a group of test animals, usually rats or rabbits; the lethal dosage is of the pure compound and is given in so many milligrams of pesticide per kilogram of the animal’s body weight. Oral LD, is a measure of the toxicity of the pesticide when administered internally to the test animals. Dermal LD, is a measure of toxicity when the pure compound is applied to the skin of the test animals. Generally, the oral application is more toxic than the dermal. (Source: Lynda Brown, 1998).


Prof. Steve Wratten (source cited below) says pesticides ‘kill non-target organisms–including the natural enemies of the pest itself. Pests can quickly recover in higher numbers. Encourage pesticide resistance. Hazardous to human health and the environment. Consumer resistance. Ongoing costs associated with pesticide use (eg. lawsuits, clean-up etc). Rate of production of new pesticide molecules is the lowest in 50 years. Restrictions on pesticides eg. banning them are increasing.’


In ‘Are organic foods healthier than the alternative?, debate between Julian Morris, Institute of Economic Affairs, and Patrick Holden, The Soil Association’, in The Guardian Saturday Review, 8th January 2000, Patrick Holden said ‘No one knows what the long-term affects are of ingesting small traces of pesticides.’ In reply Julian Morris said ‘synthetic chemicals are not carcinogenic, and anyway chemicals found naturally in foods such as broccoli and oranges are carcinogenic.’ Morris then said that pesticide residues on food are not poisonous, and that there are more carcinogens in a cup of coffee than on all the non-organic food we eat in one year.

Sir John Krebs in ‘Chewing over the facts’ in The Guardian (November 2000), referred to an article by Joanna Blythman (In The Guardian’s ‘Weekend’ magazine, Saturday November 4th 2000, p.90) in which Blythman claimed there is “enhanced safety” in organic food and claimed that 43% of conventional fruit and vegetables tested contained pesticide residues. Sir John replied by saying “what she omits to say is that they are within acceptable safety limits and at very low levels.”


Lynda Brown, Shoppers’ Guide to Organic Food (1998, Fourth Estate).

Professor Steve Wratten, Bio-Protection Research Centre, Lincoln University, New Zealand, ‘Enhancing biodiversity & its benefits in vineyards; harvestmen, earwigs, scientists & other creepy-crawlies,’ presentation by Professor Steve Wratten at the Organic & Biodynamic Winegrowing Conference July 8-10 2015, Marlborough, New Zealand.