There are many factors that influence the development of pesticide resistance. Some characteristics of pesticides that increase the likelihood of resistance development include: persistent toxicity, single-site mode of action, easily metabolized, and an effectiveness that is governed by a single gene in the target pest. Characteristics of the pest that increase the likelihood of resistance development include: rapid reproductive rates, much genetic variability in the pest population, ease of genetic mutation, capability to metabolize many molecules, and good fitness in resistant members of the population.

Horticultural practices can also increase the likelihood of pesticide resistance problems. For example, the following practices may increase the chance of pesticide resistance development:

• Dominance of a single crop with short rotation
• No crop rotation
• Poor pesticide application techniques
• Cultural practices such as over fertilization
• Multiple and/or consecutive applications of a pesticide or pesticides with a single mode of action (MOA)
• Use of transgenic plants with pesticidal activity
• Use of susceptible plant varieties
• Reliance on pesticides, rather than an integrated management approach

OEEP/EPPO (European and Mediterranean Plant Protection Organization). 1999. Efficacy evaluation of plant protection products: Resistance risk analysis. EPPO Standard PP 1/213(2). OEEP/EPPO bulletin 29: 325-47.

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