Kokua Line June Watanabe

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Hands will get dirty
culling haole koa trees

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Question: I have a lot of haole koa trees growing on my property. Other than cutting them individually by hand, is there some biological method (bugs, perhaps) to get rid of them? Or some kind of spray that will poison them? These trees are more of a hazard (fire, bugs, leaves and rubbish) than anything else. Any suggestions from your experts?

Answer: There are off-the-shelf chemicals you can use, but you really can't get away from manual labor.

We found one expert, professor Joe DeFrank, within the University of Hawaii-Manoa's Tropical Plant and Soil Science Department.

DeFrank is a weed scientist who does research in such areas as no-till farming, and weed control for golf courses and the orchid/anthurium industry.

For homeowners the general recommendation is to cut haole koa trees down to about nine to 10 inches, leaving a stump. "Paint" the stump directly with the readily available herbicide Roundup, preferably "the strongest one (strength) you can get," DeFrank said.

Cover every part of the stump "so that you get all that absorption into the stem and into the plant." Now would be a good time to do this, as opposed to the drier summer months, because recent rainy weather has resulted in active, growing plants, he said.

People may think it would be easier to kill a plant like haole koa if it was dormant and drought-stressed, but a systemic chemical like Roundup works better if the "exact opposite" condition existed, DeFrank said.

"You want an actively growing plant when you use a herbicide (like Roundup) that's based on absorption and movement to kill it," he said.

An alternative method is to spray the trunks of the haole koa with a product that contains the active ingredient triclopyr, DeFrank said. Such products can be found in most stores that sell garden supplies.

"That chemical is very good at killing leguminous weeds like haole koa," DeFrank said, and the advantage is that you don't have to do any pre-cutting.

It will probably take several sprayings before the trees defoliate and dry up, he said. After that you'd have to cut and remove the tree, but there'd be less weight to deal with.

In addition to haole koa, DeFrank says he frequently is asked about how to get rid of bamboo.

His advice: First, cut down the bamboo patch, then allow the bamboo "to regrow to the point where you have fully expanded leaves," which indicate the plant is returning food to the root system.

Look for a product with the active ingredient imazapyr, which also can be found in garden supply stores, then apply the product to the green stems, where it will be absorbed into the root system.

DeFrank cautioned, however, that you shouldn't use imazapyr if you have a plant you're fond of growing near the bamboo.

Imazapyr will persist four to six months in the soil, and if roots of other plants are nearby, chances are "they will take it up and be injured," he said. So if "the bamboo patch is next to a favorite plumeria tree, you might not want to do that."

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