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Resources · event · 2025 · Oʻahu

2025 Oʻahu Weed Control and Restoration Workshop

Priority ONE (Oʻahu Native Ecosystems) Working Group

Presentations, restoration breakout discussions, and an herbicide trial design activity — with slides, audience questions, posters, and the worksheet.

Organised by

Waiʻanae Mountains Watershed Partnership · DOFAW Native Ecosystem Protection and Management · Kualoa Ranch · Army Natural Resources Program Oʻahu · Ecosystems Extension Program

AridExtension — knowledge exchangeVery wet
NarrativeIndex
8 sections in order
§ Overview

This workshop was brought to you by the Priority ONE (Oʻahu Native Ecosystems) Working Group. Members of the organizing team represented the Waiʻanae Mountains Watershed Partnership, DOFAW's Native Ecosystem Protection and Management, Kualoa Ranch, the Army Natural Resources Program Oʻahu, and the Ecosystems Extension Program. The agenda was also developed with input from the Koʻolau Mountains Watershed Partnership.

Mahalo to those of you who completed our pre-workshop surveys — your input contributed to development of the workshop goals and content. Mahalo nunui to PCSU for sponsoring the venue.

The workshop featured a set of presentations, restoration topic breakout group discussions, and an activity geared towards increasing herbicide label fluency and setting up herbicide trials. Below is a brief overview of these sessions.

The three sessions

Invited presenters gave updates about LFA on Oʻahu (OISC), coqui frog on Oʻahu (DOFAW and partners), biocontrol development for Natural Area weeds (USDA-FS), and an overview of the inaugural meeting of the Hawaiʻi Drone Hui.

Breakout discussions centered on three restoration topics: CRB in restoration sites; nursery germination — successful methods, challenging species and trials for about 24 species; and seed-based restoration trials.

The herbicide trial activity walked groups through setting up a trial for one of nine target species, following a worksheet structured on the process presented by DOFAW-NEPM.

§ Presentations

Click through to watch each presentation or view the slides. Questions from the audience are recorded under each session — expand any question to see the answer given on the day.

LFA Update

Erin Bishop (OISC)

Slides (PDF)

Overview of Little Fire Ant status across the state and on Oʻahu, LFA biology, human–LFA interactions that facilitate invasion, and control strategies including monitoring, detection, and treatments.

From the floor · 7 questions
What is the timeframe for eradication?
Treatments every 6 weeks, for 12 months.
How do you treat in trees?
Toxicant (granular) on the ground, spray growth inhibitor (liquid) in trees.
If your greenhouse is LFA free, how often do you recommend testing? Monthly? Is quarterly sufficient?
Testing quarterly is sufficient. If you are LFA free you can even test annually.
In a nursery, what is the spacing of sample sticks/vials?
Every 10 steps.
Is there an LFA certification for nurseries?
No.
Is there language for contracts when buying plants from nurseries?
Yes — reach out to OISC for language and SOPs that will ensure folks test for LFA, or have OISC check your existing language.
What is the main vector?
Plants and landscaping. Large landscaping projects can spread ants very quickly. Not all nurseries have LFA, but those with detections are working with HDOA. A nursery having no past detection does NOT mean it is LFA free — consistent testing is needed to be confident. Quarantine and test plants from nurseries.

Coqui Frog Update

Ryan Chang (DOFAW), Jessica Miura (HDOA), Robbie Snyder (OISC), Kimeona Kane (Waimānalo Lineal Descendent, Waimānalo Neighborhood Board), Taylor Campbell (Waimānalo Agriculture Association), Timo Sullivan (Aloha ʻĀina Drones)

Slides (PDF)

Overview of the coqui frog invasion on Oʻahu, the history of control efforts, the Waimānalo community initiative, collaboration between OISC, DOFAW, HDOA and affected communities, and the application of innovative drone methodologies for survey and control with Aloha ʻĀina Drones.

From the floor · 1 question
How do you catch coqui?
With a long tube. Listen for the frog, position the tube opening in front of it and the frog will jump in. Tubes are getting harder to find as fluorescent lights are phased out. We also need plastic bottles to store caught frogs — give us your Gatorade bottles.

Biocontrol Update

Tracy Johnson (USDA-FS)

Status of biocontrol agents under development for Natural Area weeds.

  • An assortment of melastomes — Chaetogastra (previously Tibouchina), Miconia calvescens (miconia) and Miconia crenata (clidemia)
  • Falcataria moluccana (albizia)
  • Hedychium gardnerianum (Himalayan ginger)
  • Rubus spp.
  • Schinus terebinthifolius (Christmas berry)
  • Chromolaena odorata (devilweed)

Hawaiʻi Drone Hui Overview

Dan Jenkins (UH Mānoa, CTAHR)

Slides (PDF)

An overview of the inaugural Hawaiʻi Drone Hui meeting.

  • Background — history and trends in aerial application of pesticides
  • The existing (and upcoming) regulatory framework
  • Innovative applications for conservation and natural resource management in Hawaiʻi
From the floor · 1 question
What are the challenges to using drones that were discussed at the Drone Hui meeting?
Regulations that limit flights to line of sight; interaction with piloted aviation; operating at night — automated flights have proven a good workaround, and if you can fly in daytime you can fly at night; some targets are easier than others, with low-to-the-ground targets harder; variety in terrain and elevation of use; and sites have to be prepped.

Additional questions?

Feel free to reach out to continue the conversation.

EcosystemsExtensionHI@gmail.com
§ CRB in restoration

This section synthesises the CRB information shared across programs. The programs represent a mix of environments spanning developed and natural areas, and manage a mix of native ecosystem restoration sites, native palm populations, or non-native palm collections. None are situated within dense urban areas, and they are often dealing with specific challenges due to access and topography.

CRB discussion

Priority ONE breakout group synthesis

From the floor · 10 questions
Will there be testing for control methods on species other than palms?
Not too many other preferred species (banana, hala, etc.) are available at the gardens, but we might explore control methods on kalo next. There are a lot of collections in the gardens.
What herbicides are you using or testing?
Merit is a granular product, but probably not a long-term solution. Drenching takes too long and is not feasible. Crown injection also consumes staff time. There is money to fund a full-time team of two for four months performing crown injections on coconut.
Have there been any trees that came back after being attacked?
No rares have come back, but one at Hoʻomaluhia regrew after being eaten by CRB.
Is it worthwhile to remove a standing dead tree?
These are often lowest priority for removal at the gardens and could take 4–5 months. It may be worth landowners doing it themselves by netting the trunk, with the goal of the slowest decay. Cutting and chipping might get everything already in the pile but would not control the eggs. Aerial treatment of imidacloprid could work; granular and vascular treatments would not.
Does a thick canopy hide palm species beneath?
CRB tend to fly high and mostly hit taller trees. At first the decision was to halt planting more loulu at the gardens, but that will be reconsidered. Decoy trees might be a good distraction.
Are there ways to systematically search the soil?
No — we usually find them while outplanting, and through moving soil around we find grubs.
What about yellow crazy ants and CRB?
Yellow crazy ants are possibly preying on CRB, though it is unclear whether they are deliberately going after them or finding them as food after the fact.
Does sun/UV deteriorate the plastic netting?
Yes. Deteriorating netting creates large piles of nets with holes and eventually microplastics. There are two types on the market to consider: polypropylene and high density polyethylene.
Notes on traps
Only pheromone traps are in use in Mākaha, and more are found all the time. The Army Natural Resources Program has set up breeding site traps, but nothing has been caught in them yet.
What is HDOA doing?
HDOA is currently making guidelines on how to manage CRB and guiding requirements for laws. One suggestion was that they also include verbiage on proper disposal of netting materials.
§ Nursery germination

A working summary table drawn from the nursery germination posters and discussion. This is a living resource — if you have similar or differing germination experiences, or other species you want to improve rates for, let us know.

During the discussion the group considered what other information would be useful in a table like this. Potting medium was suggested as an additional category. If there is another category you would find valuable, we want to hear it.

Germination summary

Table content to be transcribed from the poster set — structure and key confirmed at the workshop.

SpeciesInoaTxGerm.SP
Inoa
Hawaiian name
Germ.
Germination rate
Tx
Seed treatment
✔️
Working method — established, generally satisfactory
🔄
Trial in progress
⏳
Future trial
KR
Kualoa Ranch
NEPM
DOFAW Native Ecosystems Protection and Management
PPH
Protect and Preserve Hawaiʻi
ANRPO
Army Natural Resources Program, Oʻahu
WV
Waimea Valley
CTAHR
College of Tropical Agriculture and Human Resilience — O. Baldos and L. Watanabe

Roughly 24 species were discussed. Rows are pending transcription from the poster images above.

§ ANRPO seed sow trials

ANRPO seed sow trials

SpeciesInoaTimePlotsTxInitial countFinal count
Inoa
Hawaiian name
Time
Duration of trial
Plots
Number of plots
Tx
How seeds were treated before sowing
Initial count
Number of seedlings at first non-zero observation
Final count
Number of seedlings at last check
SL
Seed Lab

Rows pending transcription from the ANRPO direct seeding materials.

§ Herbicide trial activity

These species have information gaps in the Weed Control Matrix, and/or were indicated as species of interest through the pre-workshop survey. Each group worked through a worksheet structured around the key steps to setting up an herbicide trial.

Two different types of trial were addressed: control method (which herbicide at what application rate) and control strategy (where the herbicide is known, but other management considerations remain — return rate, pairing control with other actions, and so on).

Species addressed in breakout groups

  • Rubus argutus
  • Spathodea campanulata
  • Ficus spp.
  • Trema orientalis
  • Syzygium cumini
  • Cinnamomum burmannii
  • Citharexylum spp.
  • Megathyrsus maximus
  • Cenchrus ciliaris
The worksheet steps

Identify the problem — species, management challenge, management goal. Research — review existing literature, use existing resources such as the Weed Control Matrix, ask around, and gather takeaways. Describe the plant — monocot or dicot, herbaceous or woody, annual or perennial, clonal. Hypothesise. Record land type, which correlates to site type on the herbicide label and informs maximum use rates. Define treatments by trial number, herbicide or cocktail, and concentration. Set monitoring protocols — frequency, duration, and metrics matched to application method.

§ Follow up

Follow up

Our intention is that this documentation can help extend the reach of these conversations, or initiate new ones. Let us know what you are thinking, if your experience matches or diverges from what is shared here, or if you want to talk to any of these programs and practitioners in more depth.

Do you see an error — a typo, or a misrepresentation of what you shared? We want to fix it.

EcosystemsExtensionHI@gmail.comlportner@hawaii.edu