A New Invasive Species – Hala Scale
By Glenn I. Teves, County Extension Agent, UH CTAHR
“Pala ka hala, momona ka wana” is a saying connecting activities on the land with those in the ocean. In this case, when the hala fruits are ripe, the sea urchin or wana is fat and ready to eat. Now, hala will need to overcome a new nemesis that may not allow its fruits to ripen.
In 1995, the Hala Scale was discovered in a shipment of hala plants from the South Pacific to Hana, Maui. From there, it quickly spread to other islands. It was recently confirmed on Molokai in Puko`o and is believed to have been on the island for more than five years. The Hala Scale (Thysanococcus pandani) causes yellowing of and serious damage to Hala (Pandanus tectorius), resulting in leaf deformation, shortening of leaves, prop roots forming in unusual places, fruit deformation and loss of plant vigor. This pest is considered a major pest of Hala and is expected to cause serious damage especially to older, weaker, more susceptible plants by sucking on the sap of plants. Long-term effects of scale attack on hala populations are likely to be severe, but only time will tell. At this point in time, many hala plants throughout the islands look sickly from this pest. The South Pacific island of Rarotonga, in the Cook Islands, apparently lost its Hala in the 1920s from a similar accidental insect introduction.
An insect becomes a pest when its natural enemies are not present. When many of these pests reach Hawaii, they may not have natural enemies here, and this allows their populations to explode. However, there are many predators of other scale species already established in Hawaii, especially Coccinellids or Lady Bugs, and some of them many zero in on the Hala Scale. Others include tiny wasps that may parasitize adult scales and eggs, but the challenge is that many dislike salt air and windy conditions where Hala is found. Many scales are controlled with horticultural oils such as Safer’s Soap or Sunspray Superfine Oil which can suffocate them by clogging their breathing holes or spiracles.
Hala, also known as Pandanus or Screwpine, is an important canoe plant brought by the early Polynesians to Hawaii, and is used to weave cordage, thatching, mats, bags, bedding and decoration, and fruits are also eaten. It also has cultural uses as well. In Southeast Asia, leaves are used in curry dishes and also to flavor rice. Hala leaves contain a compound similar to Basmati rice, considered a delicacy in many parts of the world. Fruits are also consumed and made into drinks. The Micronesian varieties are noted for their great tasting fruits. The plant is dioecious; there are male and female trees. There are over 600 species of hala, and on many atolls, its importance is second only to coconuts.