Expert warns of resistant codling moth

Risk of codling moth becoming resistant to the main insecticide chemical groups is increasing as global warming takes hold, leading insect expert Dr Jerry Cross has claimed.

East Malling Research entomologist Cross told growers at the British Independent Fruit Growers' Association (BIFGA) 20th annual technical day at Lamberhurst, Kent, on 15 January that codling moth has already become a big problem in central and southern Europe's apple growing areas, making more frequent spraying necessary.

"If resistance occurs, very few products work effectively so you have to use non-chemical methods," he said. "It will increase growers' costs if it arises here, so it's important to prevent it by using an integrated approach."

This involves integrating straight chemical insecticide use with that of biocontrol products to which the development of resistance is very unlikely, Cross explained. One new biological insecticide is CyD-X, a codling moth granulosis virus. Cross said the UK was "the last European country to get it".

He added: "This is host-specific and safe, and you can get a carry-over of infection (from one season to the next).

"Old infected larvae can survive the winter and establish infection the next spring. But the virus is slow-acting and as a result you can get superficial 'stings' on the fruit before the larvae are killed. However, where you've got moderate to high codling moth infestation it's not wise to rely on it exclusively."

Also new is an entomopathogenic nematode, which to work effectively must be applied during rain.

Easier to use is the Exosex auto-confusion trap system installed at 25 traps/ha. Male moths entering the traps become covered with the female pheromone. The system is very effective against low moth populations, Cross claimed.

He added that the cost of codling moth control products varied widely. The cheapest is cypermethrin, at £2/ha, while the most expensive is the nematode, costing £120 to £180/ha. Tracer, an insecticide, costs £64/ha.

Cross affirmed that the pest greatly favours warm conditions. Over the past 10 years or so, its second generation (of two) has been getting stronger. Active in August, it is much more damaging than the first one in June.

Apples are much more susceptible to damage when they are mature because they are softer. This is another reason why the second generation is a greater problem, and it applies particularly to the early varieties.

Cross said he favoured Bi-sex lures over the normal pheromone traps for monitoring codling moth numbers as they eliminate unnecessary spraying. But the moths do have to be sexed, which he said was "a very useful job for consultants".

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