Q.

Why are my citrus fruit falling off the tree?

Tim Martin

A.

That looks like damage from either guava moth or a fruit worm.
Guava moth is a recent introduction to New Zealand, the adult lays its eggs on the fruit, the larvae hatch and bore into fruit, causing the fruit to rot from the inside.
Unlike other insect pests, guava moth does not have a dormant period, it has a continuous life cycle.
Guava moth is active year-round as it finds other food sources and hosts.
As with fruit worm, guava moth is hard to control as the larvae that does the damage is inside the fruit, so the best measure is prevention.
Remove all fallen fruit and dispose of in the rubbish or burn, some people have resorted to microwaving, blending or freezing infected fruit before disposal.
There are pheromone traps that can be hung in the tree to attract the male which are purchased from garden centres and hardware stores, recipes for guava moth lure traps are on Youtube and the internet.
Traps need to be hung from the start of flowering and fruiting in spring right through to harvest in autumn.