Department of Agriculture

HONOLULU – The final environmental assessment (EA) allowing the release of a biological control for the invasive strawberry guava was published today by the Department of Health’s Office of Environmental Quality Control (OEQC).  Strawberry guava is a non-native plant that is invading and threatening Hawai`i’s native forests and has already overtaken hundreds of thousands of acres in Hawai`i.

The U.S. Forest Service has been testing potential natural control insects for strawberry guava for more than 15 years and has determined that the Tectococcus ovatus (T. ovatus), a small scale insect, provides natural control of the strawberry guava and will not harm any other native or beneficial plants or insects.  Even with the release of the biological control insect, strawberry guava will still be able to grow, but will be naturally controlled and will be less invasive to the forest. The insect does not harm other plants, even those closely related like the common guava.  The full EA may be found at the OEQC website at: oeqc.doh.hawaii.gov/

“This action needs to be taken,” said Russell S. Kokubun, Chairperson of the Hawai`i Department of Agriculture. “The native forest cannot protect itself from invasive strawberry guava and while most people are not able to see how bad it is, survey maps show the massive damage the forests have already suffered due to this invasive plant. Saving the native forest ecosystem is far more important in terms of protecting unique resources for future generations,” Kokubun added.

In 2005, the U.S. Forest Service first presented to the public the proposed release of the biocontrol insect. However, opposition from individuals and some pig hunters delayed the project.  More outreach was done to try to relay the seriousness of the threat and those who initially had concerns are being informed of the finalization of the EA which indicates that there is a finding of no significant adverse impact.

After 30 days of the OEQC notice, HDOA plans to do an initial release at one site on Hawai`i Island where progress will be monitored by the US Forest Service and individuals may be able to see the results.  Subsequent releases will follow.

“We hope that people understand that release of this biological control insect will not kill all strawberry guava,” said Tracy Johnson, lead researcher for the US Forest Service in Hilo. “There will still be a lot of strawberry guava around.  Slowing its reproduction and invasiveness will help restore the balance in favor of the native forest plants like `ohia.”

Government agencies and many environmental organizations are strongly supportive of this action including: The US Forest Service, US Fish & Wildlife Service, Hawai`i Department of Land and Natural Resources, Hawai`i Department of Agriculture, University of Hawai`i College of Tropical Agriculture and Human Resources, the Office of Hawaiian Affairs, Hawai`i Invasive Species Council (including the Invasive Species Committees on Maui, Hawai`i Island, O`ahu and Kaua`i), The Coordinate Group on Alien Pest Species, The Nature Conservancy and the Maui Department of Water Supply.

Strawberry guava (Psidium cattleianum, Myrtaceae) was introduced to Hawai`i in 1825 and has since advanced through Hawai`i’s native forests. Mechanical removal is extremely difficult in remote forest areas. The species has also adversely affected Hawai`i’s watersheds.  A University of Hawai`i study shows that strawberry-guava-infested forests lose 27 percent more water than native ohia forests.  USDA also reports that the millions of pounds of dropped fruit are a primary source of oriental fruit flies which invade Hawai`i agriculture crops and cost Hawai`i millions of dollars annually in quarantine treatment and control efforts.

T. ovatus is a tiny scale insect that is native to Brazil where strawberry guava came from.  The insect lives most of its life inside the strawberry guava leaves, causing leaf galls or bumps, which reduces the vigor of the plant, but does not kill it. The damage is similar to galls frequently found on `ohia which are caused by native insects.

Hawai’i researchers have been world leaders in the successful use of biological control of plant pests and diseases.  Since 1975, 51 biocontrol species have been introduced to Hawai`i without any unintended adverse effects.  Some of the targeted weeds include clidemia (Koster’s curse), banana poka, ivy gourd, panini cactus.  These previously invasive plants can still be found in Hawai`i, but naturally controlled at a level where they are not invasive. Biological control has also been successfully used to save the native wiliwili trees from the erythrina gall wasp and to control the stinging nettle caterpillar.

More extensive information is also available on the US Forest Service website at: https://www.fs.fed.us/psw/programs/ipif/strawberryguava/

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View survey maps of strawberry guava infestation areas

View a FAQ sheet prepared by the US Forest Service

 

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The following are a few quotes contained in the EA:

 

Experiences of Land Managers and Field Biologists

 

Many land managers and working biologists around the State deal with strawberry guava’s threat to the endangered plants, animals and ecosystems in their care on a daily basis. Their experiences provide perspective on the ubiquity and magnitude of the problem, as illustrated in these quotes compiled by the U.S. Forest Service:

 

“I am a State wildlife biologist for Maui Nui District – I see every day I am in the field doing work in the mountains of Lana‘i, Moloka‘i, or Maui the tremendously urgent need for biocontrol of strawberry guava. I am certain it is one of the very worst of habitat altering, invasive weeds to ever get a foothold in Hawai‘i.”

Dr. Fern P. Duvall, State Wildlife Biologist

 

“The National Park Service and other land managers in Hawai‘i need more tools to prevent strawberry guava from invading and displacing native forests as densities increase into P. cattleianum monocultures. Considerable effort in mechanical and chemical control has been expended by Hawai‘i land managers over the last 20 plus years and still the invasion footprint and native species displacing monoculture formations of strawberry guava are increasing.  Mechanical and chemical control can not keep up with the invasion of P. cattleianum.”

Steve Anderson, Program Manager for Vegetation, Haleakala National Park.

 

“Here in West Maui I have witnessed first hand how strawberry guava (Psidium cattleianum) can displace native watersheds with single species monotypic stands, displace endangered species habitats, render vast sections of land susceptible to erosion, exhibit broad habitat preferences, spread to the most inaccessible areas, and advance steadily from low elevations toward the pristine forested core of our lands.  Since its introduction to the islands in 1825, strawberry guava has grown to become a dominant species within roughly 2-5 thousand acres of West Maui’s Forest Reserve and adjacent conservation lands.  Currently strawberry guava is abundant in many places in West Maui up to 2,000 feet elevation, has strong satellite populations up to 3000 feet and is know to exist over 4,000 feet in elevation. The summit of the West Maui Mountains at Pu‘u Kukui stands at 5,788 feet and strawberry guava has been known to grow in elevations in excess of that on other islands.  Given enough time and left unchecked it seems entirely possible that strawberry guava could consume vast expanses of the watershed.  It seems further evident in my experience that this is also true statewide.

Christopher Brosius, West Maui Mountains Watershed Partnership Coordinator

 

 

“Much of my work in the past decade has been trying to foster the development of a sustainable koa forest industry in Hawai‘i.  The koa forest at lower elevations in East Hawai‘i is being rapidly invaded by strawberry guava.  Currently, harvesting of koa in these forests is unsustainable, because dense strawberry guava regeneration overwhelms the koa regeneration.  Although it has been well documented that in natural forests koa can regenerate healthy stands naturally following disturbances and harvests, harvesting in forests invaded by strawberry guava just leads to thickets of the weed.  There is too much guava to practically control by chemical or mechanical means.  Biocontrol is the only solution.  I am working with several large private landowners currently who would like to begin sustainable forestry projects in low-elevation koa forests in East Hawai‘i, but the stumbling block is the presence of the strawberry guava.”

Dr. J.B. Friday, Forester, UH Manoa

 

“As a technician in conservation efforts throughout the Hawaiian Islands for the past ten years, I have spent countless hours cutting and applying herbicide to strawberry guava growing in endangered species habitat.  In the Ko‘olau Mountains, where our agency was responsible for the protection of a number of highly endangered, rare, endemic plants, we were extremely discouraged by the waiawī’s ability to resprout from cut saplings.  We would helicopter into remote areas, spend three days camping, spending the entire time “killing” waiawī –but when we returned to follow up, it was like we had done nothing! The large piles of cut stems sprouted roots and new growth, and the forest floor was a carpet of keiki waiawī!  We spent thousands of dollars, used gallons of polluting herbicides, and were unable to maintain even a stand-off with this invasive weed. Endangered plants are unable to coexist with this weed–in the darkness under a stand of strawberry guava, NOTHING else grows.”

Springer Kaye, UH Hilo TCBES graduate program

 

“I regard strawberry guava as perhaps having done more destruction to endemic forest species in the state of Hawai‘i over the past century than any other invasive plant. We on Maui are so committed to stopping the as yet very limited invasion of Miconia calvescens.  We recognize, however, that strawberry guava has very similar impacts to miconia but is far beyond mechanical and chemical control and is much more widespread than miconia and still spreading.”

Dr. Lloyd Loope, USGS Pacific Island Ecosystems Research Center Haleakala Field Station

 

“My own experience and publications have shown that strawberry guava is a highly invasive species that is actively excluding native species and is altering the way that Hawaiian forests function.  I am finding strong evidence that the shade produced by strawberry guava and other species is impeding native species regeneration.  I believe the consequences of inaction will lead to wholesale transformation of Hawai‘i’s low and mid-elevation wet forests into alien-dominated forests that function very differently in terms of providing nutrients, water, and other ecosystem services.  This alteration of function will lead to greater invasion of plants and animals in Hawai‘i’s forests and a loss of native biodiversity.”

Dr. Rebecca Ostertag, Ecologist, UH Hilo

 

“In the past three decades I have seen Psidium cattleianum go from being a serious invasive to becoming a biological catastrophe for ‘ohi‘a forests.  They have gone from being rampant invaders, to completely replacing native forest, including the forest floor, the understory, and soon will replace the dwindling canopy in many areas.  I don’t see much future for wet forests, where strawberry guavas have invaded, unless there is some sort of control.”

David Paul, President Big Island Native Plant Society

 

“The goal of our partnership is the protection of forested watershed on Kohala Mountain. Strawberry guava (Psidium cattleianum) is one of our priority weeds…We have seen the speedy spread of this weedy tree not only near areas of human disturbance, but also into the forest, where it is able to establish in closed canopy forest areas far from people.  In these environments, it has the capacity to completely overtake native trees and to change the structure and function of the native habitat.  Additionally, it is expensive and difficult to control with mechanical and chemical means.”

Melora Purell, Coordinator, Kohala Watershed Partnership

 

“My observations over the last 38 years indicates the dying out of native forests in many areas of O‘ahu due to the continued spread of strawberry guava and other weeds, among other factors…Strawberry guava leaf litter also is extremely poor habitat for the native terrestrial snail species.  Wherever strawberry guava has spread, the native terrestrial snails have declined or died out.”

Dr. Daniel Chung, Biologist, former Nature Conservancy and Bishop Museum