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Building Weed Control Profiles

Species profiles exist for many invasive species in Hawaiʻi. Examples of such resources include the DLNR HISC Invasive Species Profiles, the Hawaiʻi Weed Risk Assessments, and Plant Pono. These profiles largely communicate distribution, current invasion status, invasiveness, invasion traits, etc. Here, we highlight details to inform control methods and management strategies (e.g., distribution, dispersal mechanism, etc.). Use the side-bar menu to see all the topics featured here and navigate between topics. Currently, the information on this page reflects discussions at the 2024 Hawaiʻi Island Weed Control Forum. These profiles are a work in progress, they will continue to be built by incorporating information and references to grey and published literature regarding each topic--if you have similar or different experiences, let us know. You can reach us at EcosystemsExtensionHI @ gmail.com, we look forward to working with you to incorporate your experiences into this effort.

Australian Tree Fern (ATF)
Cyathea cooperi

What we know
What we need to know

Distribution

  • All over Kaumana, Volcano area

  • HISC Species Profile: "Spreading from landscaped areas in Volcano, Laupahoehoe, Kona and other areas."

  • What is distribution and density across Hawaiʻi Island?

Ecology

  • Spores are wind dispersed, animal and people dispersed

  • What is the rate of its spread?

Treatment

  • Manually control--need to be consistent

    • Be sure to remove apical meristem, macerate or set it above ground--avoiding contact with the soil, so it cannot resprout (Mootoka et al., 2003)

    • cut fronds off first to minimize disturbing/spreading spores (Mootoka et al., 2003)

  • HBT works with imazapyr

  • 2% polaris +2% round up works

  • from Mootoka et al., 2003:

  • susceptible to dicamba and 2,4-D sprayed directly on the stem terminals​​

  •  triclopyr not as effective​

  • unclear if resprouting of felled ferns is possible in high-rainfall sites (Mootoka et al., 2003)

External Factors

  • They are still selling it at Home Depot–yesterday 

  • Much of public mistakes it for hāpuʻu (in yard landscaping)

  • Plant Pono Species Profile

  • How to keep them from being sold

  • Laws to prevent the plant from being a landscape option

  • What can Watershed Partnerships do to help?

Motooka et al. (2003). Weeds of Hawai‘i’s Pastures and Natural Areas; An Identification and Management Guide College of Tropical Agriculture and Human Resources, University of Hawaiʻi at Mānoa (https://www.ctahr.hawaii.edu/invweed/WeedsHI/W_Sphaeropteris_cooperi.pdf)

Strawberry guava
Psidium cattleyanum

What we know
What we need to know

Ecology

  • Every part is a propagule (resprouts readily)

  • Allelopathic–kills other plants

Treatment

  • When cutting down in very wet areas, need to treat both ends with herbicide

  • Circumference cut at base and G4 application–leave standing to die/dry

  • Methods for composting to prevent or manage regrowth--not everyone has chipper access, wants to, or can use herbicide

Biocontrol

  • How can we help get more Tectococcus out into forests? Community program for property owners? Volunteer work? Training programs?

  • State needs to grow access to Tecto 

  • Does T. ovatus affect different varieties differently? [Yes, ask Tracy for more info]

Other

  • Abundant and good for mulch

  • Can be good building material–if treated

  • Makes good firewood/bbq

  • Natural fences

  • Great for lomi lomi sticks

  • Fruit excellent for jelly and jam

  • 90% of fruit fly populations originate from strawberry guava

  • Major agricultural pest because of fruit flies

Tree tobacco
Nicotiana glauca

What we know
Ecology

  • Likes disturbances (fires, cattle, goats, dozing)

  • Post-disturbance, it gets less overtime as other weed species move in

  • Need to treat it less than 1 meter so it does not impact the ōkaʻi (less)

  • Seeds get into animal fur and is spread around

Treatment

  • Hand-pulling can be problematic if sprouts from the root if not all is pulled

Other

  • Sucks, when break one truck

What we need to know

  • How much ʻaiea do we need to have to have a meaningful impact on Blackburn Sphinx Moth populations?

  • Do mice spread the seeds?

  • What is its relationship to fire?

  • Genetic difference in Tree Tobacco eating sphinx moth vs ʻaiea eating sphinx moth

  • How long do seeds last in the soil?

Gorse
Ulex europeanus

Distribution

Ecology

Treatment

What we know
What we need to know

  • How far down the Wailuku is it? 

  • How high up the river bank?

  • What is it current distribution and density?

  • 400+ year seed life

  • seeds carried by waterways (e.g., Wailuku down to Kaumana)

  • What is the seed bank longevity?

  • Seed bank survey

  • Spray when young

  • spray often--need consistency 

  • remove seed bank with spraying post-germination

  • Can be shaded out in long-term at older life stages

  • 2% Garlon 3A + silicone surfactant 

  • .25% Milestone + silicone surfactant

  • Can we go back to burning it--to induce seed germination pre-control?

  • Can we utilize cattle/ungulates to graze/keep down new growth in controlled/managed areas?

  • Results from control trials on Mauna Kea (DDHL)

  • What is most efficient control method given biomass

Other

  • Thorns make it a good natural barrier to keep people out

  • Are there other uses for it? E.g., made into wine, flowers harvested for lei or perfume

Homolanthus populifolius

Distribution

Ecology

Treatment

Other

What we know

  • Present in Manukā NAR

  • spreading north, South Kona, Kāpua

  • WRA info

What we need to know

  • What is the distribution in Hawaiʻi/on island?

  • Where is it and where should we address it as an eradication target?

  • Impacts seem to be underestimated

  • What is seed longevity?

  • What is fecundity/seed production numbers?

  • What are treatment methods? 

  • Efficacy of foliar vs hack and squirt?

  • Common names include Bleeding Heart, Queensland poplar

  • Bleeding heart is also common name for plants in the genus Dicentra, herbaceous perennials native to North America and not found in Hawaiʻi

Faya tree
Myrica faya

What we know

Distribution

  • Also present on Oʻahu in the Waiʻanae mountains​

Ecology

Treatment

  • cut stump with 50% Garlon4 + water

  • cutting stump is labor intensive

    • requires chainsaw​

Control strategy

Other

  • One of IUCNs list of world's 100 worst invasive

  • We live on an island-nothing is impossible, while it seems that Faya is out of control and a lost cause, we just need funding, state support and manpower

What we need to know

  • What is its status statewide?

  • ​What is the progression of invasion in Hāmākua?

  • Does it have elevational limits?

  • Does vog affect Faya?

  • How long do they live?

  • Is it possible to control its spread by birds? How? Is clipping bird wings an option?

  • Is Faya flammable? What are its fire traits?

  • Are there more efficient treatment options?

    • IPA?​

    • Aerial spray?

    • Biocontrol?

  • Not eradicable, but still containable: How and where?

  • Need to engage Volcano Golf Course to help eradicate/control there

  • How much money is the government willing to invest in the environment?

  • What partnerships are needed (and where) to make the biggest/most valuable impact if eradication isn't possible?

Rubus spp.

What we know

Distribution

Ecology

  • Bird-dispersed

  • stems can get up to 8" in diameter at base

Treatment

  • Rubus ellipticus: 

    • ​cut-stump with clippers/handsaw and

    • 25% G4 

    • treat both ends as stems can re-reoot

  • Rhizominous--control sometimes needs repeat treatments​

  • Cutting without harbiciding leads to multiple regrowth off of root system

  • Can be hard to get to base

What we need to know

  • How many species are in Hawaiʻi?

  • How many of those species should we be worried about?

  • What is seed bank longevity?

  • What birds are dispersing it?

  • How far are birds moving it?

  • What are best practices for homeowner control? [BIISC working on this]

  • Are there better herbicide mixes?

  • Is Milestone effective?

Other

  • Edible and can be tasty: eat the invasive! Make it a competition, like a fishing tournament. Also gets the community involved

Melastomes

What we know

Ecology

  • Chickens and Kale pheasants eat Clidemia berries and they don't sprout once pooped out

  • Seeds can often be polyembryonic

What we need to know

Treatment

  • Garlon 4 foliar treatments

  • Garlon 3 works too, but covers less species

  • Round up at 5% also works

  • Garlon 3a + Round up mix at 1% for roadside and trial

  • Cattle grazing/pasture rotation effective for Tibuchi

  • Methods for composting to prevent or manage regrowth--not everyone has chipper access, wants to, or can use herbicide

Control strategy

Once established, melastomes are extremely pervasive very hard to control at large scale

  • Biocontrol!

  • Do folks want a biocontrol for T. urvilleana? 

Other

  • Clidemia is a soap bush--elsewhere in the world it is often used for medicine and said to have anti fungal and antimicrobial properties

  • What are beneficial properties of Clidemia? 

    • A weed is a weed until we find a use for it​

Post-fire weed control and restoration

What we know

Invasion Ecology

  • Invasive grasses love fire

    • respond rapidly and often replaced native shrubs

  • Need to be prepared to eliminate new incipient​

Fire ecology

  • When cutting down in very wet areas, need to treat both ends with herbicide

  • Circumference cut at base and G4 application–leave standing to die/dry

Fire traits

  • ʻilima, ʻaʻaliʻi, māmane, naio and ʻuhaloa are all somewhat fire resilient

  • some mosses can come back rapidly following fire

Strategies

  • Longer weed control will have direct impacts on the number of stems and growth rate of native plants in the area

  • Weed control is needed in order to establish natives

  • Seed bank now! Prepare for fire before it happens

  • Prevention seed-collection needed and timely distribution

  • Fire break species

Other

What we need to know

  • What is the role of ungulates in shaping post-fire vegetation communities

  • What are the effects of fire on soil communities and chemistry?

    • How does that effect what species regrow?​

  • What conditions promote native shrubs/grasses post-fire?​

  • What native species have fire tolerant seeds?

  • Does pili grass have fire tolerant seeds?

  • Understanding the timing/ capitalization of bare ground available post-fire

  • Need landscape-level control techniques

    • aerial spray​

    • targeted grazing

  • How to scale up seeding/restoration for resilient native communities?​

  • At what percent cover native post-fire do we need to achieve to have meaningful longterm impacts?

    • Can we get to a certain level and then "walk away?"

  • How much wild seed collection vs seed orchard/production?​

  • Need money to conduct control

Grasses

What we know

Ecology

  • Flammable--fire fuel

  • Affected by Two-Line Spittle Bug (TLSB)

  • Effective competitors for moisture and other soil resources

  • Effective at ecosystem alteration

  • Seeing fountain grass and kikuyu hybridizing at Puʻu Waʻawaʻa

Treatment

  • When cutting down in very wet areas, need to treat both ends with herbicide

  • Circumference cut at base and G4 application–leave standing to die/dry

Management Strategies

  • ʻilima, ʻaʻaliʻi, māmane, naio and ʻuhaloa are all somewhat fire resilient

  • some mosses can come back rapidly following fire

Other

  • Longer weed control will have direct impacts on the number of stems and growth rate of native plants in the area

  • Weed control is needed in order to establish natives

  • Seed bank now! Prepare for fire before it happens

  • Prevention seed-collection needed and timely distribution

  • Fire break species

What we need to know

  • Is hybridization between fountain grass and kikuyu a problem for management?

  • What are the effects of TLSP?

    • What are its environmental conditions/elevation?​

  • Under what conditions can native grasses out-compete non-native/invasive grasses?​

  • What are the effects of fire on soil communities and chemistry?

    • How does that effect what species regrow?​

  • What conditions promote native shrubs/grasses post-fire?​

  • What native species have fire tolerant seeds?

  • Does pili grass have fire tolerant seeds?

  • Understanding the timing/ capitalization of bare ground available post-fire

  • Need landscape-level control techniques

    • aerial spray​

    • targeted grazing

  • How to scale up seeding/restoration for resilient native communities?​

  • At what percent cover native post-fire do we need to achieve to have meaningful longterm impacts?

    • Can we get to a certain level and then "walk away?"

  • How much wild seed collection vs seed orchard/production?​

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