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Potential risks, costs and benefits of reducing the abundance and biomass of moth plant using biological control, and of introducing the moth plant rust, Puccinia araujiae

Potential beneficial effects

Beneficial effects for the environment

Source of potential benefit Comments
Maintenance of habitats
Reduced competition from moth plant leads to increased survival and diversity of native and other desirable plants in affected habitats. This is major expected benefit of the biological control programme. Moth plant scrambles over short stature native vegetation in many habitats, killing plants, replacing vegetation and halting regeneration. Moth plant overtops taller plants in forest margins, and can break down trees. Successful biological control will reduce those adverse effects wherever the weed occurs, acting far beyond the reach of existing management efforts. Control will reduce the future development of adverse effects of the weed as it spreads.
Reduced cover for pests on dunes Back dunes support heavy moth plant infestations that harbour rabbits and predators of shore-nesting birds, such as mustelids. Successful biological control would reduce the effects of predators and pests by reducing cover.
Sustainability of flora and fauna
Reduced competition with native seedlings including vines Moth plant scrambles over the ground and short stature native vegetation in many habitats, killing plants, replacing vegetation and halting regeneration. Successful biological control will reduce competition wherever the weed occurs.
Reduced mortality of seedlings and improved succession of vegetation Ditto
Reduced incidence of trapping by flowers of valued insects such as bees As part of its pollination strategy, moth plant flowers traps some foraging insects by the proboscis. Some die, reducing the number of pollinators in the environment. This probably does not significantly reduce overall pollination services.
Reduced damage to underlying foliage from spraying Moth plant commonly grows like a curtain using valued vegetation as a framework. Spraying this moth plant damages both. Successful biological control will reduce the need for such spraying.
Improved access to underlying resources for birds Moth plant curtains hide flowers and fruits on underlying vegetation. Benefit limited because probably not a significant proportion of overall resource.
Ecosystem processes
Benefits to parasitoid, predator and disease relationships in trophic webs Increased plant diversity as moth plant monocultures break up will increase the diversity and complexity of trophic webs, but effects will vary locally, spatially and temporally. Moth plant monocultures are not yet common, so this benefit (though real) is not regarded as significant.
Increased nutrient turnover in the soil beneficially affects natural nutrient cycles, increasing the growth rate and survival of valued forest seedlings. Leaf destruction will increase turnover under moth plant infestations, slightly enriching soil and aiding establishment of alternative vegetation. Effects limited to soil beneath the weed, and is temporary. Replacement vegetation will also aid cycling so net benefit obscure and probably not large
Reduced contamination of air, soil and water from reduced moth plant spraying Although a likely real local benefit of successful biological control, infested sites make only a small part of overall estate.
Intrinsic value of ecosystems
Improved look and feel of native bush for visitors Successful control limits the development or reduces the occurrence of unsightly monocultures of moth plant. Not a widespread effect
Increased C accumulation in affected trees Reduced shading following control increases tree health, but benefit limited because the number of severely affected trees currently limited.
Further spread south following climate change avoided Successful control will reduce seed production and the development of new serious infestations
Inherent genetic diversity in New Zealand
Loss of endangered species slowed. Not significant. No species known to be at risk primarily because of moth plant.
New Zealand's biodiversity is increased Nor significant. Species increases by one.
Reduced cover by moth plant improves cross-pollination Not significant. Moth plant curtains unlikely to be limiting cross-pollination at present.
Reduced cover by moth plant improves availability of nest spaces for birds Not significant. Moth plant curtains unlikely to be limiting cross-pollination at present.

Beneficial effects for Human health and safety

Source of potential benefit Comments
Reduced abundance of moth plant reduces incidence of skin burn by latex and allergic effects This benefit is likely, but NZ Poisons Centre reports few such allergic reactions nationally (this report)
Reduced abundance of moth plant reduces incidence of human poisoning This benefit is likely, but NZ Poisons Centre reports that incidents are relatively rare and are not severe.
Reduced frequency of control operations, lowers the incidence occupational health issues for gardeners and conservation workers No significant benefit. Current situation unknown, but such benefits are likely to be rare nationally.
Reduced importance of moth plant reduces use and adverse effects of herbicide A real but not a significant benefit. Herbicide use against moth plant in New Zealand is not currently extensive or notably hazardous.

Beneficial effects on the relationship of Māori and their culture and traditions with the environment (see separate assessment)

Beneficial effects on society and communities

Source of potential benefit Comments
Successful biological control reduces costs of  moth plant management to regional and territorial authorities A significant benefit (this report)
Successful control reduces the need for moth plant control operations, leading to better targeting of community resources and use of conservation volunteers. A significant benefit.  Many community projects focus on moth plant control; see commentary in this report
Reduced abundance of moth plant reduces nuisance value to householders (including safe disposal, damage to clothes, skin irritation), reducing time allocated to control, and reducing non-target damage from backyard herbicide application. Lifestyle benefits to householders are real; see this report.
Successful control leads to fewer instances of dermal allergies in dogs. A likely benefit, but NZ Poisons Centre reports that cases are not frequent

Beneficial effects on the market economy

Source of potential benefit Comments
Reduced control costs to businesses required to control moth plant (shelterbelts frames, other) Control would mitigate costs to businesses of complying with RPMS, as well as production costs to shelterbelts and cropping frames
Reduced control costs to infrastructure managers required to control moth plant Biological control could mitigate costs to infrastructure companies such as Ontrack and Transit (Hill 2011)
Reduced control costs/increased production in forests Not a significant effect. Moth plant is not seen as a limitation to forestry (Hill 2011)
Reduced contamination of export fruit by pappus hairs and seeds Contamination of kiwifruit by seeds is an issue for kiwifruit exporters requiring control by growers
Reduced machinery maintenance costs for contractors, reduced tangling of machinery trimming shelterbelts Not likely to be a significant
Damage to tweedia leads to greater sales in nurseries Web search indicates that tweedia is an old fashioned garden species that is not widely available in garden centres and so is not a major revenue earner for nurseries
Management of control agents creates business opportunities for Landcare Research A real effect, but a small contribution to Landcare Research revenue

Potential adverse effects

Adverse effects on the environment

Source of potential adverse effect Comments
Maintenance of habitats
Value of moth plant as a nurse crop adversely affected Not significant. Weed not widely acknowledged as a nurse crop
Reduced ability of moth plant to stabilise cliffs Not significant. Weed not widely acknowledged as a stabiliser
Reduced protection of dunes from wind and water erosion Not significant. Weed not widely acknowledged as protection against erosion. Moth plant control likely to be gradual, with natural replacement of vegetation.
Sustainability of flora and fauna
Attack by newly established moth plant rust significantlyreduces native plant populations. Experimentation indicates no such effect is likely. Native plants are not at risk
Sub-lethal attack by the moth plant rust reduces leaf area, leading to reduced efficacy of herbicides, and higher rates of herbicide application. Even if this theoretical effect was real, herbicide is applied to only a small proportion of moth plant nationally. No significant effect nationally
Reduced habitat quality for some native fauna. Not significant. Replacement vegetation will also support invertebrate fauna. No fauna of special significance found on moth plant in surveys (Waipara et al. 2006).
Ecosystem processes
Food web interactions are adversely affected by the introduction of moth plant rust. Adverse effects are conceivable but not expected. Increased plant diversity as moth plants monocultures break up will increase the diversity and complexity of trophic webs, but effects will vary locally, spatially and temporally.
The process of control increases nutrient turnover in the litter, adversely affecting nutrient cycles. Le Accelerated leaf fall may increase turnover under moth plant infestations, slightly enriching soil and aiding establishment of alternative vegetation. Effects limited to soil beneath the weed, and temporary.
Intrinsic value of ecosystems
No significant effects have been identified  
Inherent genetic diversity
Indirect competition causes extinction of native rusts Not a significant risk. No indication that vulnerable or endangered species are associated with moth plant infestations (Waipara et al. 2006), and any measurable indirect competition would be restricted to the immediate vicinity of the host plant.
Rust hybridises with native Puccinia species Not a significant risk.

Adverse effects on  human health and safety

Source of potential adverse effect Comments
Rust generates allergic response No significant risk. Literature search reveals no such cases
Rust requires spraying with adverse effects to humans No significant risk. No undesirable attack on non-target plants is expected.

Adverse effects on the relationship of Māori and their culture and traditions with the environment (addressed in separate section)

Adverse effects on society and communities

Source of potential adverse effect Comments
Less moth plant foliage available to feed monarch butterflies. No significant risk. Moth plant foliage unlikely to become rare.
Attack by newly established moth plant rust significantly reduces the usefulness of the ornamental tweedia. Not tested. Damage to tweedia in New Zealand gardens is possible
Fear and distrust of exotic diseases and their possible non-target effects. Firmly held opinion in a proportion of the population.
Control reduces the aesthetic values of moth plant No significant risk. Moth plant is not valued by the public.

Adverse effects on the market economy

Source of potential adverse effect Comments
Successful biological control reduces revenue for contractors and suppliers Not a significant effect. Revenues directly related to moth plant management are not a key revenue source for many or any contractors or supplies.