War on moth

Guava moth (Coscinoptycha improbana) blew across the Tasman in its adult form in the late 1990s and now ruins a range of soft fruit and nuts from Northland to the Waikato year-round.

Cable Bay, Northland-based entomologist Dr Jenny Dymock, who works with the Northland Regional Council, says guava moth infests citrus including lemons, oranges, mandarins and grapefruit over the winter months.

"But by about this time of year, guava moth are also infesting loquat, which then gives the insect a big population boost heading into plum, peach and pear production over Christmas and early summer."

Dymock says because they develop within affected fruit, guava moth larvae are not easily targeted by insecticides.

"The larvae render fruit inedible with their excrement and can also lead to the development of damaging moulds and fungi. They can also cause premature fruit drop."

Dymock says experience has taught that following good orchard hygiene is one of the best ways for both home gardeners and commercial growers to try to protect their crops from the moth's larvae.

"It's important to rake up any fallen, rotting fruit and either remove it or bury it as this removes any pupae which are in the soil."

She says use of a fine weave mesh (like curtain netting) wrapped around fruit does prevent guava moth laying eggs on fruit, although realistically this is not an option for commercial growers.

"It's important not to use bird netting as guava moths can get through its broader weave. Secure your mesh by simply taping around branch of tree."

Dymock says the best time to cover fruit is just as fruit is swelling, not earlier when a tree is flowering.

And she says it's important to remember that while guava moth pheromone traps are useful for monitoring guava moth in the region, they offer little in the way of control.

"Guava moth is now too widespread through the region."

Dymock says advice about a range of insect and other pests is available from the Northland Regional Council's website via: www.nrc.govt.nz/nasties Biosecurity officers can also be contacted via the council's freephone (0800) 002 004.