Question: My parents’ tangerine tree, which fruits faithfully every New Year, is looking very sick. What can we do? It seems to be dying and I can’t tell why. The leaves have "crud" and the branches are dying back but it still gave us lots of yummy fruits. Can you help us save our tree? — Karen Y., Palolo

Answer: We have yet another alien pest that has gotten into Hawaii and it attacks citrus plants and their relatives, including mock orange (part of the citrus plant family Rutaceae).

This pest is called the Asian citrus psyllid. The insect was first noted in Hawaii in 2009. I consulted with entomologist Lynne Constantinides and she has concerns about this pest for our home garden fruits and commercial fruit orchards.

The damage from the psyllid is the stunting and twisting of young shoots and severe curling of leaves. The adult insects are small (3 to 4 millimeters) with mottled brown wings, and they are active, jumping insects. Eggs are bright yellow and can been found deposited on emerging plant shoots. Nymphs are green or dull orange.

The Asian citrus psyllid is known to vector Citrus Greening Disease, which has devastated citrus in Asia, Africa and Brazil. CGD is caused by a bacteria, Candidatus Liberibacter asiaticus. Symptoms include mottling and/or interveinal yellowing of citrus leaves and misshapen, green and bitter-tasting fruit.

There is no known cure for CGD, which has not yet been found in Hawaii. This is another reason we all need to pay attention to quarantine rules and not try to bring fruit home to Hawaii illegally.

Another pest to citrus plants is the citrus black fly that attacks citrus plants including oranges, jabong, kalamansi and kaffir lime.

This pest sounds like the crud you describe on the leaves. If your tree is young, you can do the soapy water treatment (one tablespoon of liquid dish soap per gallon of water) spray the soapy water onto the pests on the leaves and in an hour or so wipe all the mess away.

First of all, clear at least 3 inches of lawn grass away from the trunk and replace the grass with mulch; leafy mulch is best. Grass competes with trees, and also the tree’s bark is often wounded by mowing the grass.

Every nick and cut on the bark is a wound and an entry point for pests and diseases. Try not to use a leaf blower in your garden; they tend to blow away soil and the beneficial organic matter.

For a valuable tree like yours it’s worth getting a soil test and seeing which nutrients might be deficient. Or you can apply a general balanced fertilizer that includes micronutrients, such as iron, zinc and calcium, which are often deficient in our older Hawaii soils.

Compost helps nutrients work better and also keeps them where they are needed: in the root zone of the tree.

Clean the pests off the leaves that you can reach. You can also blast them off with a strong spray of water from your garden hose.

Prune off the dead branches and throw them away. You might be able to save your tree if you act now.

The fruit are fine to eat, but they might be a stress response: The tree is under attack so it makes extra flowers and fruit.

If the tree can’t be saved, buy a grafted citrus tree to replace it. They are resistant to many pests because they are on a strong root stock.

I hope that Gov. David Ige will restore some of the agricultural inspection jobs that were cut. If we can stop the pests before they get here and become established, it’s a win for all of us.

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