Monday, April 14, 2014

Trouble with Palms

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

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. 

Monday, April 7, 2014

Stink Bug

 A wide range of fruit and vegetables, as well as leaves and flowers, are susceptible to the Southern Green Stink bug, nezara viridula. In some countries it is called the green vegetable bug.  

Damage is achieved by inserting their needle-like mouth part into the plant tissue and sucking out the plant juices. Some stink bugs can cause wart-like growths as the plant reacts to the piercing. Although the green color of the pests blends with the foliage making them difficult to find, bugs can be visible feeding in the garden on beans, cabbage, peppers, tomatoes, okra or in the trees on such fruit as mangoes and macadamia nuts. The adults are active fliers, and when disturbed, will fly away or fall towards the ground.

Control is sometimes difficult. Horticultural oils, including Neem oil, work well, but the solution needs to contact the insect. (Read more about Neem on this website.) To spray when the insect is not there will do no good. Oil, as well as soap, is a contact insecticide. Harsher chemicals like Sevin and Orthene will also control this pest. Yet in many areas biological control is effective, and chemical control is seldom necessary. 

In Hawaii, introduced parasites (good guys) are well established and are generally effective. Predators include spiders and the big headed ant. The ants prey upon the eggs and immature stages of the stink bug, taking them back to their nests. The stink bug is so named because of the strong odor emitted from scent glands when disturbed. 

Monday, March 31, 2014

Growing Cotton in Hawaii

Cotton is actually a perennial shrub, but growers often cultivate the plants as annuals.  In Hawaii, the cotton plant, Gossypium tomentosum, or Ma’o in Hawaiian, is a perennial shrub lasting about 3-5 years, depending on growing conditions. This is not the commercial cotton that is grown in other parts of the world. (G. hirsutum is used in about 90% of the industry)

The native Hawaiian cotton, however, is used in breeding programs which has resulted in commercial hybrids which are less attractive to insect pests.

Ma Ľo can be found growing in coastal plains and dry forests primarily on the leeward sides of the main Hawaiian Islands.  Ma’o naturally grows in hot, dry, windy coastal areas tolerating the salty spray. Conversely, it does not do well in locations with continuous high rainfall and in waterlogged soil.
Periodic pruning is necessary to control the height, to keep the shrub full and to prevent low lying branches from spreading.

In 1838, a commercial cotton industry was actually started in Kailua on the Big Island. Although it lasted for about a century, cotton never became an important trade item. Even though the fibers were used by early Hawaiians for stuffing pillows, the cotton was not used as a fabric.  For more information on Ma’o, see the website for native plants in Hawaii at

There is also a CTAHR publication entitled, “Ma’o (Hawaiian Cotton).