Biocontrol battle waged against Strawberry Guava

The state wants to release a Brazilian scale insect to help in the control of the invasive strawberry guava tree that is crowding out native plants on Maui and other parts of the state.

Officials with the West Maui Mountains Partnership (WMMP) say strawberry guava has become a dominant species in roughly 2-5 thousand acres of the West Maui Forest Reserve and adjacent conservation lands since its introduction to the islands in 1825.

The action is proposed by the Hawaii Department of Agriculture to mitigate the impacts of the strawberry guava on native forests, the water supply and agriculture.

Maps from the Draft Environmental Assessment show the estimated potential range of Strawberry Guava infestations across the state. Click to enlarge image. Courtesy State of Hawaii, Office of Environmental Quality Control.

“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,” said Christopher Brosius, the coordinator for the WMMP program explained in the report.

“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,” said Brosius.

Brosius said during his work, he has witnessed first-hand how strawberry guava can displace native watersheds, endangered species habitats, and render vast sections of land susceptible to erosion.

State Wildlife Biologist Dr. Fern Duvall of Maui was quoted in the report saying, “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,” said Duval.

Strawberry guava (dark green) amid 'ohi'a (light green/gray) in Wao Kele o Puna. Image courtesy DEA, Hawaii Office of Environmental Quality Control.

The U.S. Forest Service reported a similar response from Haleakala National Park officials.  “The National Park Service and other land managers in Hawai‘i need more tools to prevent strawberry guava from invading and displacing native forests,” said Steve Anderson, Program Manager fro Vegetation at Haleakala National Park.

“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,” said Anderson who argues that mechanical and chemical control cannot keep up with the invasion.

The impacts have also been reported on the island of Lanai by Jay Penniman, the Maui District Endangered Species Research Specialist for the State Department of Land and Natural Resources.

“I see strawberry guava as the most significant threat to the continued viability of the Hawaiian petrel colony on Lana‘i,” said Penniman.

“We need every available tool if we are to preserve Lana‘ihale as a petrel colony and as a watershed. The scope of the problem is so great that without biocontrol to add to our tool bag we face a nearly impossible task of habitat restoration,” said Penniman in the report.

A draft Environmental Assessment has been prepared and is open for public comment for a full month beginning today and ending on July 23, 2010.  The complete report is available at the following link:  http://oeqc.doh.hawaii.gov/Shared%20Documents/EA_and_EIS_Online_Library/Statewide/2010s/2010-06-23-ST-DEA-Biocontrol-Strawberry-Guava.pdf