Cross-resistance
Cross-resistance (continued from last month)
Because all compounds within the chemical sub-group share a common MoA, there is a high risk that the resistance that has developed will automatically confer cross resistance to all the compounds in the same sub-group.
It is this concept of cross-resistance within chemically related insecticides or acaricides that is the basis of the IRAC Mode of Action Classification.
The objective of successful Insecticide Resistance Management is to prevent or delay the evolution of resistance to insecticides, or to help regain susceptibility in insect pest populations in which resistance has already appeared.
Effective IRM is thus an important element in maintaining the efficacy of valuable insecticides.
In practice, alternations, sequences, rotations or even mixtures of compounds from different MoA groups provide a sustainable and effective approach to IRM.
This ensures that selection from compounds in any one MoA group is minimized. The IRAC classification in this chapter is provided as an aid to insecticide selection for these types of IRM strategies.
Recommendations for successful resistance management (Modern Crop Protection Compounds, Wolfgang Kramer and Ulrich Schirmer):
- Consult a local agricultural advisor or extension services in the area for up-to-date recommendations and advice on IPM and IRM programs
- Consider options for minimizing insecticide use by selecting early-maturing or pest tolerant varieties of crop plants
- Include effective cultural and biological control practices that work in harmony with effective IRM programs. Adopt all non-chemical techniques known to control or suppress pest populations, including biological sprays such as Bt’s, resistant varieties, within-field refuges (untreated areas) and crop rotation
- Where possible select insecticides and other pest management tools that preserve beneficial insects
- Use products at their full, recommended doses. Reduced (sub-lethal) doses quickly select populations with average levels of tolerance, whilst doses that are too high may impose excessive selection pressures
- Appropriate, well-maintained equipment should be used to apply insecticides. Recommended water volumes, spray pressures and optimal temperatures should be used to obtain optimal coverage
- Where larval stages are being controlled, target younger larval instars where possible because these are usually much more susceptible and therefore much more effectively controlled by insecticides than older ones
- Use appropriate local economic thresholds and spray intervals
- Follow label recommendations or local expert advice for use of alternations or sequences of different classes of insecticides with differing modes of action as part of an IRM strategy
- Where there are multiple applications per year or growing season, alternate products of different MoA classes
- In the event of a control failure, do not reapply the same insecticide but change the class of insecticides to one having a different mode of action and to which there is no (locally) known cross-resistance
- Mixtures may offer a short-term solution to resistance problems, but it is essential to ensure that each component of a mixture belongs to a different insecticide mode of action class, and that each component is used at its full rate
- Consideration should be given to monitor the incidence of resistance in the most commercially important situations and gauge levels of control obtained
- Withholding use of a product to which resistance has developed until susceptibility returns may be a valid tactic if sufficient alternative chemical classes remain to provide effective
See this article in Tree Fruit Nov 2016
