The Beautiful Vireya

Vireya are part of the rhododendron family, classified as a subgenus. They are native to Southeastern Asia - New Guinea, Borneo, Sumatra and the Philippines, growing quite often in the cooler mountainous areas. On the Big Island of Hawaii, vireya, also called tropical rhododendrons, are successfully grown from Volcano down to the coast.  There are about 300 species of vireya. Azaleas are part of this group.

Vireya grow well in the sun.  Yet locations of intense sunlight along with high afternoon temperatures should be avoided. In this case filtered sun is best. On the other hand, planting vireya in the shade will produce leggy shrubs with inferior flower production. No hot summer sun, no heavy shade.

It is important to plant vireya in soils and potting mixes that have excellent drainage. In addition to growing them in the soil, and sometimes in cracks and crevices, they can also be found growing as epiphytes. An epiphyte is a plant that grows upon another plant such as a tree, but is not a parasite on that tree.  The epiphyte derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it.

Vireya are well adapted for growing in pots and may even grow well indoors in a well-lit room. They come in a variety of beautiful, vibrant colors such as salmon, pinks, orange and yellows.

For those interested in learning more about vireya, join the Hawaii Chapter of the American Rhododendron Society or search to see if there is a chapter in your area.

Japanese Maple in the Tropics

Being a deciduous tree, the Japanese maple is indeed adapted for cold climates. Hawaii, as well as other tropical locations, does not provide the best growing environment; yet the trees will grow in these areas. I have one Japanese maple that is now 9 years old. Admittedly, it is not the most vigorous tree, and I think it is continually looking for winter. Sometimes it goes dormant in spring or even in the middle of summer, but it still grows. A question might be, how many years can it survive without experiencing a dormant period?

There are over 1000 cultivars of Japanese maple. Obviously some will adapt to tropical regions better than others. Usually, nurseries select those varieties best suited for their area.

Regardless of the climate, another problem is an insect called Chinese rose beetle. This beetle makes holes in the leaves weakening the tree. 

In the evening, when beetles are feeding, placing a cover or netting over the small trees will exclude the pest. Another choice for control is to use a systemic insecticide with the active ingredient imidacloprid. Granules can be applied to the pots and watered in. 

On this website, gardenguyhawaii.com I have a detailed report on this pest; search Chinese rose beetle in the space on the left of the screen.

Trouble with Palms

"The bottom fronds of our triangle palm started to die, and then suddenly the whole palm fell over," a friend complained.

A significant pest of Pritchardia palms is the banana moth, Opogona sacchari. The triangle palm is also attacked by this moth. It seems that the female moth targets wounded or stressed palm tissue to lay her eggs. Stresses can include drought, flooding, mechanical wounding, poor nutrition, and herbicide injury. The larvae generally feed on decaying and dead plant tissue but will feed on living tissue, too, causing extensive damage. In affected palms, larval tunneling, along with the characteristic frass (insect droppings), can often be seen. Fully developed caterpillars measure just over an inch. The adults have greyish brown wings are 3/8 to 5/8 inches long.

The main treatment is prevention: keep palms growing well; give them adequate fertilizer, and supplemental water during a drought. Gardeners also need to be careful with the weed wacker! Female moths are looking for wounds to lay their eggs. Bt (Bacillus thuringiensis), an organic insecticide, can be applied to these wounds, as well as those caused during pruning.

For more information about this pest see the CTAHR Cooperative Extension Service publication, “Banana Moth – A Potentially Fatal Pest of Pritchardia and Other Palms”, by Scot Nelson and Mark Wright.  CTAHR stands for the College of Tropical Agriculture and Human Resources at the University of Hawaii.