Introduction to pesticide resistance management

On 27 May 2015, a Crop Protection Resistance Management Workshop was held in Auckland.
The proceedings and outputs from this meeting are now available here.

What is pesticide resistance?

Among the billions of individuals that make up a pest population (be it disease, insect, mite, weed etc), there may exist some individuals that are less susceptible a pesticide than others. If the same pesticide is continually applied, then the more susceptible individuals will be killed, leaving only resistant individuals to breed and multiply. If the resistance is heritable then eventually a large proportion of the population may be resistant to the pesticide. The resistant pests may then cause unacceptable damage to crops.

Therefore, pesticide resistance or, more accurately, the resistance of pests to pesticides occurs where the pest population has changed genetically so that it is less susceptible or sensitive to a pesticide or class of pesticides. This means that a higher dose of pesticide is now required to control the pest population, or even that the highest practical dose will not kill all pest individuals.

Types of resistance

There are two types of resistance (or susceptibility) to pesticides:

the normal variability in the susceptibility of individuals of a population to a chemical control, and
changes in the overall susceptibility of pest population in response to exposure to a chemical.

Here, we are concerned with the latter, in which pesticides fail due to genetic change in the pest population, rather than changes in the crop plant or chemical.

Reasons for control failure

Not all instances of control failure are due to the development of pesticide resistance in the target pest population. Other reasons for failure may include:

poor spray application due to operator error and poor sprayer calibration;
unsuitable weather during or immediately after spraying such as excessive wind or rain washing off the pesticide;
faulty product;
inappropriate product.

Poor control may allow the more resistant pest individuals to survive, and continual use of the same control may then allow true pesticide resistance to develop.

Resistance management strategies

One of the objectives of the New Zealand Plant Protection Society is to pool and exchange information on the biology of weeds, invertebrate and vertebrate pests, pathogens and beneficial organisms and methods for modifying their effects. The Society has prepared a series of web pages to outline existing problems with pesticide resistance in New Zealand and to suggest strategies for preventing and managing pesticide resistance problems.

These New Zealand pesticide resistance strategies are divided into sections on managing: