Community battles guava moth

By: Dee Pigneguy

 We will have to behave as though we are at war if gardeners are going to control guava moth. The whole community needs to be involved.

Guava moth (Coscinoptycha improbana) is a small, black and white speckled inconspicuous moth with a 15mm wingspan, which arrived here from Australia in the late 1990s. Its presence was noted by Hibiscus Coast gardeners early in 2016.

The moth lays its eggs in cracks and crevices on the surface of fruit, as the fruit starts to swell and ripen. The caterpillar, which is pinkish and grows to 10mm in length, then burrows into the fruit.

A small hole in fruit can be early indication, although early damage is hard to find. Generally we discover we are hosting this pest when the caterpillar chews its way out. Fruit becomes inedible as the caterpillar leaves a rotting fruit full of poo. Another indication to watch for is immature fruit drop. Vigilance is the key here.

Although similar to codlin moth, the guava moth has a continuous life cycle.  Insecticides are almost useless against the caterpillar as it spends such a short period on the surface of the fruit, and its early damage is not readily seen.

After the caterpillar chews its way out of the fruit, it drops to the ground and the larvae pupate in the leaf litter and debris under the trees.

It has become a major pest for home gardeners because it has such a wide host range. During the winter it infests citrus and then uses early loquat fruit to continue its lifecycle until launching an infestation on plums and peaches as these summer fruit begin to set. Feijoas provide the necessary target fruit in autumn.

This fruit does not need to be in your backyard – as long as the trees are in the neighbourhood, the moth will continue its lifecycle throughout the year.

There are three ways the community can pull together to defeat (control) this moth: 1 Remove all rotting infested fruit both on the tree, and the ones that drop around the base of the tree. Put this into the rubbish, not the compost. 2 Prevent the female moth from laying her eggs on the fruit by covering trees with a fine mesh (like curtain material) as the fruit is ripening. 3 Keep the area underneath the tree clear of debris. I am experimenting with using the mats that come with My Food Box as mulch material – hopefully the caterpillars will not be able to chew through them to get to the soil underneath. You could try cardboard, sacks or thick stacks of newspapers.

Guava moth back stories, www.localmatters.co.nz February 3, 2016, November 1, 2018

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