Tropical Gardening: Perils lurk in paradise

  • Courtesy of VOLTAIRE MOISE Many fungi are beneficial, such as this one that helps break down dead leaves and branches to improve our tropical soils.

Local folks and visitors often feel that our islands have few dangers except for rare volcanic eruptions, earthquakes and hurricanes.

But perils still lurk in paradise, including for plants.


While there are few poisonous native plants, some common exotic landscape plants are toxic, such as oleander, crotons and angel trumpets. Some people can experience skin reactions like exposure to poison ivy from cashew and mango trees.

There is another kind of peril that isn’t quite so obvious.

Many of the plant diseases we have today in Hawaii did not exist before humans arrived. Once here, they are not easy to control. The best disease prevention measure you can take with ornamental plants, fruits and vegetables is to start with healthy disease-resistant plants.

According to University of Hawaii plant pathologists, once a plant becomes badly diseased, it is difficult to nurse back to health. For this reason, every effort should be made to prevent introduction of disease-causing organisms on plant material or in soil. Identifying the cause is vital to knowing the proper cure.

Good cultural and sanitation practices will help prevent trouble, such as removing diseased parts including leaves or branches as soon as they appear infected. Treat pruning wounds with a specially prepared material to stop entrance of wood-decaying organisms and wood-feeding insects.

For treatment of fungal diseases, fungicide applications should begin when disease development first appears and continue as recommended by the manufacturer.

Algae commonly grow on the surface of soil that is moist for periods of time. This is very common during the rainy season. These minute green plants often develop in such profusion that they form a rather thick, greenish to blackish mat. Growth of such magnitude in turf is detrimental to the grass because algae actively compete with the grass for space and nutrients.

In addition, if the algae mat dries, it forms a crust that hinders or prevents the movement of water into the soil.

The same conditions that favor the growth of algae also favor the growth of fungi that cause turf grass diseases. In fact, a close association has been noted between frequent disease outbreaks and the presence of algae. Therefore it is desirable to control both problems with one practice.

Reducing the moisture level would be the ideal method; however, in many situations, this is not possible. Other control measures must be used. The use of fungicides that are effective against turf diseases and algae is an efficient method of control.

Your local garden supply or nursery can assist you on the correct material to use. You also can call the Master Gardener hotline at the UH College of Tropical Agriculture. In Hilo, the main number is 981-5199. In Kona, the main number is 322-4893.

Prevention of disease-causing organisms is vital and includes keeping them out of Hawaii. Some folks get unhappy when they can’t bring certain plants or seeds into Hawaii, or if they can they have to go through all kinds of red tape, fumigation or extended quarantines to get the plants through.

A few folks figure it is a bother to get permits and go through the proper procedure to bring plants to Hawaii. They smuggle a few plants thinking it won’t make any difference.


This attitude couldn’t be further from the truth or more dangerous. If it weren’t for people bringing in disease- and insect-infested plant materials, our islands would not be plagued with such creatures as fruit flies, burrowing nematodes or many other pests that damage food crops as well as ornamentals.

We should support our state and federal agricultural quarantines. Importing plants illegally could bring a devastating disease to Hawaii. By following the law, hundreds of new plant introductions are being made each year. These can enrich our lives without bringing with them unwanted insects and diseases that could bring disaster to our economy.

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