Hawaii Gardens: Invasive avocado lace bugs wreak havoc on prized trees

Question: My avocado tree is sick. Help!! It has these ugly bronze patches on the leaves and the lower branches are dying!

This is a young tree, a super sentimental one for us because our late uncle bought this special air-layered one from a fruit specialty nursery, Frankie’s in Waimanalo. Mahalo. — B.K.

Answer: We have another new alien pest insect and it attacks avocado trees.

It is called the avocado lace bug (Pseudacysta perseae). To check if your tree is infested, look for bronze patches on the upper shiny sides of the leaves, then check the undersides for little sap-sucking insects and their eggs. They gather and suck out the plant sap from the young juicy leaves. When the leaves turn brown, they become less photosynthetically productive. Bad infestations will kill that leaf, or the entire young branch.

The scientific name of avocado trees is Persea americana, so you can see by the name of the pest that it is specific to feeding on avocado trees. It’s in the laurel, or Lauraceae, family.

The avocado lace bug was first detected in Pearl City in December 2019 and was subsequently identified on Hawaii island and Maui. The pest insect has not yet been reported on Lanai, Molokai or Kauai. Let’s hope we can keep it away from those isles and their avocado trees. Once a pest gets loose, it’s often too late to control.

Please everyone, no smuggling! (Plant people can be the worst offenders.) Don’t sneak flowers, plants, seeds or fruits, etc., into our islands or between islands. Whatever you want to bring home, get it properly inspected and certified pest- and disease-free.

“It has become clear that we need to work on food security, but the arrival and spread of invasive species like the avocado lace bug is one of far too many reminders that we must also prevent and control invasive species if we hope to support farmers and home gardeners,” said Christy Martin, public information officer of Coordinating Group on Alien Pest Species. “Implementing the six years of actions remaining in the 10-year Hawaii Interagency Biosecurity Plan will be difficult, but necessary.”

How to treat your tree

As with human diseases, first we identify the cause of the plant’s disease, and then we search for a scientifically sound treatment that will kill the pest but not hurt us or the environment.

So, with avocado lace bugs, if you can reach the leaves, first shoot the pests with your garden hose on full blast; spraying the undersides of the leaves to try and wash away the bugs and their eggs.

Then spray those same leaf undersides with a safe, simple solution of soapy water (1 tablespoon of liquid dish soap per gallon of water). Small 2-gallon pump sprayers work well for this — you can find them at City Mill.

Let the soapy mixture sit on the undersides of the leaves and allow it to do its job of smothering and killing the pests.

You can also rub off the bugs with your hands, or using a soapy rag or sponge. Smooshing the pests and leaving them there is a form of biodynamism. The crushed pests give off an alert pheromone, signaling other insects to stay away from your prized avocado tree.

After you eliminate the bugs, avocado trees thrive if kept in the best health possible:

>> Keep turf grass away from the trunk and weeds at a minimum.

>> Use leafy mulch and compost to improve your living soil.

>> Water when it’s very dry (as it has been recently on Oahu).

Avocado trees are subject to fungal root diseases, so make sure the soil drains well. Planting avocado trees on a slope is a good plan. If you don’t have a handy slope, plant on a mound of good, well-drained soil, or add cinder and compost to hard-packed clay soils.

Growing at home

Avocadoes do not “come true” from seeds. In other words, if you save the pit from that delicious, buttery avocado you ate, it will not grow into that same variety of tree. They are fun and easy to grow from a seed, but use this as a houseplant, or for the sheer joy of growing something easy. Just don’t expect that same awesome fruit. They also take many years to produce fruit when grown from a seed.

For harvesting purposes, consider buying a tree of a good, known variety from a professional nursery or garden shop.

Heidi Bornhorst is a sustainable landscape consultant specializing in native, xeric and edible gardens. Reach her at heidibornhorst@gmail.com.