Although codling moth resistance to insecticides is widespread in other countries, it has probably not yet developed in the UK. Chemical control therefore remains the principal means of control in the UK because it is both cheap and effective.
Control with larvicides including pyrethroids, chlorantraniliprole (Coragen), indoxacarb (Steward or Explicit) or spinosad(Tracer)
Several insecticides including deltamethrin, chlorantraniliprole (Coragen), indoxacarb (Steward or Explicit) and spinosad (Tracer) are approved for control of codling moth or other caterpillars on apple in the UK and act by killing larvae.
- For codling moth control, the newly hatched larvae must be exposed to a lethal dose before they burrow into the fruit, either by ingestion or contact action.
- The use of synthetic pyrethroids should be avoided as they are harmful to predatory mites and other natural enemies.
- Note also that pyrethroids are broad-spectrum compounds which are harmful or toxic to humans and the environment.
- The first spray for each generation is timed to coincide with the onset of egg hatch. This time is determined from pheromone trap catches.
- The first above-threshold catch (single catch of 5 or more moths per trap per week from May to July) indicates the date when egg laying commences.
- Eggs take on average 7-10 days to hatch, but the length of time varies greatly with temperature.
- The first spray is applied 7-10 days later (use the shorter interval in warm weather) to coincide with the onset of egg hatch.
- The duration of egg development can be calculated more accurately if desired from daily maximum and minimum air temperatures.
- Cumulate the percentage egg development that occurs each day starting from the first day that an above threshold pheromone trap catch is obtained.
- The day can usually be determined within a day or two by looking at daily temperatures and identifying particularly warm days in the week preceding the weekly record of the catch.
- Moth flight generally occurs when dusk temperatures are >15 deg C. However, accurate calculation of the date of hatching is not very important as most insecticides are fairly persistent and give control for 2-3 weeks providing they are applied before significant egg hatch has started.
- The first spray against the first generation neonate caterpillars will generally be 5-6 weeks after petal fall in the second half of June, but may be earlier if the weather is warm.
- An effective residue of insecticide needs to be maintained on the leaf and fruit surface throughout the duration of the egg hatch period.
- A single spray is normally sufficient where infestations are light but two or more sprays may be necessary for more severe infestations as indicated by continuing high pheromone trap catches.
- The interval between sprays depends on the effective persistence of the product used. In hot summers there may be a second generation in August which can be very damaging.
- This may justify a further spray but care must be taken to avoid infringing harvest intervals, especially on early varieties.
Control with the insect growth regulator pyriproxyfen (Harpun)
Pyriproxyfen (Harpun) is an insect growth regulator (IGR) that mimics juvenile hormone. Juvenile hormone is a necessary chemical produced during an insect’s development, but becomes toxic when present during metamorphosis.
- Pyriproxyfen is ‘bio-residual’ providing pest control several weeks after application.
- Pyriproxyfen inhibits egg hatch, inhibits metamorphosis of nymphs to adults and reduces the fecundity of adult females (eggs laid are sterile).
- The strategy is to target eggs or early larval stages to suppress the population.
- There is no immediate lethal effect but effect can be seen during mating or with larval degradation during hatching.
- Adsorption of the product is best when freshly laid eggs are treated up to 24 hours after laying.
- Adsorption is reduced with egg ageing.
Insecticide resistance
Codling moth populations are widely resistant to conventional and insect growth regulator insecticides in southern and central Europe. The resistance has forced growers in those regions to adopt alternative control strategies, mainly using pheromone mating disruption and/or codling moth granulovirus. Resistance has not been shown to occur in the UK.
Avoiding the development of insecticide resistance
Although codling moth has probably not yet developed resistance to insecticides in the UK, resistance is widespread in other countries, especially where the moth has multiple generations.
- There is a risk that resistant moths will be imported on fruit or nursery trees from these countries but the probability of this happening is low.
- The chance of the resistance developing in the UK can be greatly reduced by alternating the group of insecticide used for control and not relying on insecticides from one group continually.