Defoliated trees are an all too familiar site lately. The cause is not our Hawaiian winter, but the latest invasive pest, the Erythrina Gall Wasp. Chances are you won't see the wasp (about 1-1.5 mm), but the damage you will see is devastating.
You will first notice crumpled leaves with bumps or "galls" on your coral and wili wili trees. Coral trees are prized in the landscape for their majestic shape and bright red flowers. Vertical Wili Wili are ideal windbreaks or screening trees that grow quickly in tight spaces. The State of Hawaii is concerned that both will be decimated in the next few years.
After the first discovery of the gall wasp here in 2005, experts recommended removal of galled leaves and treatment with systemic pesticides that would enter the plants system. The results have not been consistent. As it may take a systemic pesticide days or weeks to translocate throughout the plant, often the new leaves were susceptible to immediate wasp attack. When those remaining leaves were killed off, the tree can not photosynthesize and the plant will weaken and die.
These Vertical wili wili once screened this utility wall. After infestation, they were cut back, but did not recover. (Photo by Performance Landscapes).
The state is now collecting native wili wili seeds and researching biological predators to kill off the wasp. This is not the first, nor will it be the last attack on our vegetation. Like the recent housing demand from out of state buyers, our great climate can attract and play host to many invasive plants and animals. Many invasive species evolved in harsher climates and thus overtake the local flora and fauna.
A row of newly planted Coral Trees, Erythrina variegata, completely devastated. (Photo by Performance Landscapes)
Biological control has worked before. Ironically, a parasitic wasp was chosen to combat the whitefly plague of the early eighties. Many recall when Kahala Avenue looked like it was snowing with whiteflies and their dust. The wasp effectively has reduced the whitefly population and kept it in check. Another wasp of the Eurytoma species has been located in Africa by state entomologist, Mohsen Ramadan to test against the Erythrina wasp as well.
We are still in combat with the new "Giant Whitefly" identified in 2002, and the Sago Palm Scale infestation that started in 1998. Pesticides help, but only go so far.
Healthy Sago Palm (Cycas revoluta). (Photo by Performance Landscapes)
Infested Sago Palm (Cycas revoluta). (Photo by Performance Landscapes)
Biological controls are generally more effective since the predator remains in the environment to control the pest. As you can imagine, rigorous testing protocol must be followed before the control is released in Hawaii. The last thing we need is a predator that attacks native or beneficial insects, or turns into a pest itself. Remember mynah birds were introduced to eat bugs and mongoose to eat rats. In those days, Hawaii was the testing ground.
The Strawberry Guava (Psidium cattleianum) is a popular landscape plant susceptible to the microbial disease known as rust. The strawberry guava is itself considered by many as an invasive species to the native Hawaiian landscape. (Photo by Performance Landscapes)
This continual struggle with landscape and agricultural invaders reinforces what we already know. Hawaii's desirable and fragile environment that is attractive to all! Let's appreciate what we have, and work to keep it beautiful.
For more information, go to the Department of Agriculture New Pest Advisories Page.
If you have pest problems, contact a local landscape or pest control professional.
