Browning coconut fronds caused by alien beetles

QUESTION: Why are these coconuts dying? What can we do? Look at them by the Hilton Hawaiian Village lagoon and Ala Moana Bowls shower. Those brown fronds in the middle of the tree are concerning me. It would be so sad if all these coconuts died. — Les Tamashiro

ANSWER: When you see older fronds yellowing and browning and drying up, that is natural. The coconut palm is reabsorbing and reusing the nutrients in the fronds before they would naturally drop off.

When the fronds are like these, with middle-age, midtree fronds looking brown and tattered, that is a different story.

Our tree trimming crew saw this happening at the Hale Koa Hotel a few years ago, and we were very concerned. So we did some investigating. I went up and looked at the drying fronds, and then we cut and brought some down to the ground for closer (and safer!) examination.

There were some long, beetle-type insects hiding in the folds of the fronds. We took some to our expert entomologist and found out that they were Brontispa beetles, a fairly new and damaging alien pest that had gotten to Oahu in 1985. Auwe!

It is Brontispa chalybeipennis, or the coconut hispid. Some bio-control miniature wasps have been carefully introduced to help control this ravaging pest.

As with many pests, the immature beetles do the most damage. Eggs are laid in the young folded fronds, then the larvae emerge and start eating. The fold of the fronds protects the insects from being seen and eaten by birds like mynahs, and they feast away, growing and damaging the coconut frond. The nibbling and scraping of the delicate growing tissues of the young fronds make them look brown.

What to do? It’s not practical or safe to spray insecticide up in the crowns of coconut trees. So just like with humans, do everything to keep the coconut healthy. Mulch the soil and protect the trees from equipment damage (lawn mowers and weed eaters). Do minimal pruning. Every frond (even the insect-damaged ones) photosynthesizes and makes food for the tree. Only dry fronds should be cut off.

Use the same tree trimmers every time, if you can, and empower them to know the trees and report any problems, like puka in the trunk and up near the crown. Clean tools between groves of trees to minimize the spread of disease and insects. Clear lawn grass away from the trunks. Coconuts need regular water to thrive and stay healthy.

Coconuts, or niu, Cocos nucifera, are the tree of life for us here in Hawaii. Did you know that the same healthful amino acid in mothers’ breast milk is found in green coconut juice? Coconut is a health food.

We should grow more coconuts to eat and drink here in Hawaii. Health food and grocery stores are now full of coconut juices and milk and oil, but none of this is produced in Hawaii — so far.

At home, keep your niu low for easy harvesting. How? Minimal pruning. The more you prune and cut fronds, the faster and taller and weaker the coconut will grow. Lau niu or niu fronds make the most beautiful nahenahe (sweet) music of Hawaiian nature.

Niu can not only be a source of beauty, but also supply emergency food and drink in times of natural disaster.

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