I think I have guava moth in my mandarins, what can I do?

Q.

Hi, last year almost every mandarin on my tree had a grub inside a segment, what do you think infested my tree and what can I do to prevent it this year and when. I had heard it may have been the guava moth. Thanks.

Sharon McCann

A.

Hi Sharon, it does sound like your mandarin fruit were infested with guava moth larvae from your description, it is fast becoming a huge problem commercially and for the home gardener. Unfortunately the guava moth has a continuous life cycle, it does not have a dormant period like other insects and just moves to another host. The adult moth lays eggs on the outside of fruit and when they hatch, they burrow into the fruit, which makes them very hard to control. Insecticides are not effective as the larvae are on the outside of the fruit for a very short period of time. To minimise the damage of guava moth you can get guava moth pheromone traps that are hung in the trees to attract the males and break the lifecycle of the moth, these are available at garden centres and DIY stores. Don't leave fallen fruit on the ground as the larvae emerge from the soil when conditions are right, the lifecycle starts again with the adult laying eggs on fruit. Some people have used fine mesh bags over the fruit once they are pollinated to prevent the moth laying eggs on the fruit, these are sold at garden centres and $2 shops. Do not compost fallen fruit, dispose of or burn, keep the area under trees well mown and mulched.

There is a home made lure that may help, hang it in fruit trees to attract the moths as follows:

  • 1 litre of boiling water
  • 1 teaspoon of Vegemite (or Marmite)
  • 100 grams of sugar (2/3 cup)
  • 1 teaspoon vanilla essence
  • 1 teaspoon ammonia (such as Handy Andy or Cloudy Ammonia).
    Dissolve Vegemite, sugar, vanilla essence in boiling water. Add 1 teaspoon of ammonia. Mix well. Divide the liquid between four plastic milk bottles that have had a 5cm flap cut into the side (opposite the handle, make the flap like a hinge). The top of the flap (hinge) should be approximately 8-10cm up from the bottom of the bottle. Tie the bottle to the tree using a short tie, otherwise it swings around in the wind, make sure rain cannot get inside the flap. Hang it 1.5-2 metres up from the ground as that is the height the moths fly. Hang the lure as soon as buds burst and flowers appear, continue replacing every month until harvest. Within a few nights moths should find the lure. 
    Lianne.

 

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