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). 

Monday, March 24, 2014

Rainbow Shower Tree

Rainbow shower trees (Cassia x nealiae), native to southern region of Asia, are the beautiful multicolored trees along Bayfront in Downtown Hilo. The rainbow is actually a hybrid between the golden shower (Cassia fistula) and the pink shower (Cassia javanica). There are different varieties, each with a different array of stunning color combinations: orange, pink, white, peach and sherbets.

The tree itself is fast growing, can reach up to 65 feet high and spreads out its branches like an umbrella. It is fairly drought tolerant but grows best in a hot tropical or subtropical climate.  Trees can be propagated by air layering or grafting.

In addition to the trees lining Kamehameha Avenue along Hilo Bay, rainbow shower trees are growing at Liliuokalani Park.  Besides these, a few other types exist in Hilo:

The white shower tree, producing creamy white blossoms with a hint of yellow, can also be found in Downtown Hilo.

The pink shower tree producing large showy pink flower clusters can be found on the Hawaii Community College Campus.

The golden shower tree produces brilliant yellow flowers and can be seen at the Kawamoto Swim Stadium and near Mo’oheau County Park.

Monday, March 17, 2014


The neem tree (Azadirachta indica) is a fast growing shade tree native to Southeast Asia and India. Compounds (Azadirachtin) extracted from the seed have been found to possess pesticidal qualities; the greatest concentrations of these substances are found in the seed.

Also extracted from the seed kernel is the oil. Neem oil, like other horticultural oils, works by suffocating the insect, coating its body and blocking the breathing openings. Products are available which contain neem oil alone or with azadirachtin.  In tests involving the control of aphids, products containing both had a greater efficacy than either ingredient alone.  Neem oil can also prevent the germination of some fungal spores such as powdery mildew. 

Azadirachin, the active ingredient in many neem products, actually consists of more than 25 closely related compounds.  This ingredient works in several ways. 1. It can act as a feeding deterrent against a number of insect pests. 2. It can disrupt the molting process so that the immature larvae do not develop into adults.  3. Some insect larvae may also be killed by direct contact with the spray. 4.  Adult insects are normally not killed but mating may be disrupted. 5. Azadirachtin also has a repellent effect on certain insects and mites. Insect pests affected by azadirachtin include aphids, beetles, caterpillars, lace bugs, leafhoppers, leafminers, mealybugs, psyllids, thrips and whiteflies.  Generally, neem will have less of a detrimental effect on beneficial insects (parasites/predators) compared to the broad spectrum pesticides.
Multiple applications of neem are generally recommended. Frequent spraying is more effective because neem does not persist on plant surfaces. Like other botanical insecticides, it is quickly broken down by sunlight and washed away by rain. For smaller plants, neem seems to work well as a soil drench; the product is absorbed by the roots and translocated systemically throughout the plant.

Another product sold as a fertilizer is neem cakes. They are the residual seed meal remaining after extraction of oil from seeds. 

Monday, March 10, 2014

Parasitic Plants

Cassytha filiformis is a parasitic, leafless, flowering plant fairly common in the beach environment. It is often noticed as yellow blotches growing near the sea coasts. There is also another group of parasitic plants in the genus Cuscuta, known as dodder. These parasites infest a broad range of plants throughout Hawaii as well as tropical areas worldwide.  They appear as small orange colored strands growing over the host plant.

Although these parasites have some green coloration (often masked by the orange color), which indicates that photosynthesis does occur, they are entirely dependent on other plants for their nutrition, water and even physical support.  They vine around their host and produce adhesive structures called haustoria which penetrate the outer layer of cells of the host and extract water and nutrients from the plants phloem and xylem tissue. The host is slowly being depleted of its nutrients and water, while the parasite garnishes nutrients to grow, flower and produce seed.

Some common names for this parasitic plant in Hawaiian are kauna’oa pehu, malolo and pololo. It can often be seen parasitizing tree heliotrope, beach naupaka, ohi’a, noni and screw pine as well as fruit producing trees like citrus, mango, avocado and nutmeg. The seeds can be transported great distances by ocean currents, tidal waves, birds, strong winds, even hurricanes, and by humans.

Heavy infestations can smother host plants causing a decline and even death of the host. C. filiformis is a threat to lowland reforestation projects. It is damaging and capable of killing native, endemic and naturalized coastal and woody plants.

There are some benefits to this group of plants.  Traditionally it has been used in Hawaiian ceremonies - worn as ornamentation and in decorative garlands or lei. It is valued for its diverse healing applications; in Fiji it is used to treat jellyfish stings and as a food source.
·        Manually remove parasitic plants, especially before seed production.
·        Fire has been used to rid an area of the parasite, but will of course kill or at least damage the host also. The same is true for herbicides which may be effective, but can also damage the host.
·        C. filiformis is intolerant of shade.
·         Grazing sheep will feed on this pest.

Photos by Forest and Kim Starr

Monday, March 3, 2014

Scarring of Gladiola Blooms

The gladiolas which are pictured are infested with an insect called thrips, the major pest for these blooms. Thrips are tiny, slender black insects, about 1/25 of an inch long, obviously, difficult to see with the naked eye.  Thrips cause white streaking on the leaves and blooms. Flowers can also be misshapen, discolored and occasionally will fail to open. 

Thrips feed by puncturing the plant tissue and sucking out the cell contents.  Preferring to feed on rapidly growing tissue, thrips often cause stunting.  These insects are the culprits which also cause silvery to brownish scarring on avocado and citrus fruit surface, but this cosmetic damage does not harm the internal fruit quality.

Horticultural oils, azadirachtin (Safer BioNeem), neem oil and insecticidal soaps can be somewhat effective for the temporary reduction of the number of thrips if applied when damage first appears. Sprays must be applied to thoroughly cover susceptible areas of the plant including new leaf growth and buds.  Note: these insecticides only kill newly hatched thrips and recently emerged adults, thus repeat applications are required, usually 5 to 10 days apart depending on the temperature.  In the future, moving the location of the gladiola bed each year will discourage the spread of thrips.

Avoid the use of insecticides such as malathion and carbaryl, because they are highly toxic to natural enemies and can cause dramatic increases in spider mite populations and are generally not effective against most thrips.