Impact Assessment - Dodder (Cuscuta spp.) in Victoria (Nox)

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Assessment of plant invasiveness is done by evaluating biological and ecological characteristics such as germination requirements, growth rate, competitive ability, reproduction methods and dispersal mechanisms. Assessment of plant impacts, however, is determined by the extent to which a plant affects a land manager’s environmental, economic and social resources.

The relative importance of these resources varies depending upon the value people place on them and, as such, the assessment process is subjective. For example, a farmer is likely to place a higher emphasis on the impact of a plant on production (economic resource) than its impact on areas of natural vegetation occurring on the farm. Conversely, a Landcare or Friends group would value environmental or social resources more than economic resources.

Recognising that the value of resources vary between different land tenures, plant impact assessments allow a prioritisation of resources by land managers. Assessments can apply at a local, regional or state level, and the relative values of each resource identified may differ at each level.

The impact assessment method used in the Victorian Pest Plant Prioritisation Process uses three broad resource categories: social, environmental and agricultural, each with a number of related attributes. For example, social resources include such attributes as how the plant affects human access for recreation, or if it creates a health risk due to toxicity or by producing allergens.

Question	Comments	Reference	Rating
Recreation
1. Restrict human access?	A twining parasitic annual herb with thread-like stems and no root system. It would not restrict human access.	P & C (2001)	L
2. Reduce tourism?	The plant produces a dense mass of stems coloured yellow, green or pink. Its presence is obvious and would have a major negative effect on the visual aesthetic of an area.	P & C (2001)	MH
3. Injurious to people?	The plant does not present any spines or burrs. It is not known to be toxic to humans and seedlings have been observed growing in droppings of cows, sheep, goats and kangaroos.	P & C (2001)	L
4. Damage to cultural sites?	Its presence would present a moderate visual effect. It would not have any negative impact on the structure of a site.	P & C (2001)	ML
Abiotic
5. Impact flow?	Terrestrial species.	P & C (2001)	L
6. Impact water quality?	Terrestrial species.	P & C (2001)	L
7. Increase soil erosion?	Parasitises existing plants covering them in a dense mass of stems; unlikely to affect soil erosion.	P & C (2001)	L
8. Reduce biomass?	Produces dense mats covering host plants. Replaces biomass.	P & C (2001)	ML
9. Change fire regime?	Low growing annual that does not produce significant organic material. No evidence of this plant contributing to an increase in the frequency of fire risk.		L
Community Habitat
10. Impact on composition (a) high value EVC	EVC=Riparian woodland (E); CMA=North Central; Bioreg=Goldfieds; VH CLIMATE potential. “They…affect a wide range of broad-leaved plants…[and] grow under a wide range of environmental conditions.” “Severe yield reductions occur when crops are infested.” Major displacement of forbs.	P & C (2001) Dept. of Ag. WA1	MH
(b) medium value EVC	EVC=Hillcrest herb-rich woodland (D); CMA=North Central; Bioreg=Goldfieds; VH CLIMATE potential. Impact as in 10(a) above.		MH
(c) low value EVC	Does not appear likely to occur in any low value EVC in Victoria.		L
11. Impact on structure?	“They…affect a wide range of broad-leaved plants…[and] grow under a wide range of environmental conditions.” “It is seldom found on woody plants, grasses, cereals.” It reduces crop yields severely. Potential to affect the majority of the ground and mid strata.	P & C (2001) Dept of Ag. WA	ML
12. Effect on threatened flora?
Fauna
13. Effect on threatened fauna?
14. Effect on non-threatened fauna?	It affects a wide range of broad-leaved plants, but generally does not parasitise grasses. Animals will graze the plant. May have a minor impact on the habitat of native fauna.	P & C (2001)	ML
15. Benefits fauna?	Seedlings have been found growing in kangaroo droppings. Minor food source.	P & C (2001)	MH
16. Injurious to fauna?	Cattle and horses forced to eat the plant often develop digestive upsets.	Dept. of Ag. WA	ML
Pest Animal
17. Food source to pests?	No evidence to suggest pest animals use the plant as a source of food.		L
18. Provides harbor?	An annual that forms a dense mass of stems, it may provide limited harbor for rabbits.	P & C (2001)	MH
Agriculture
19. Impact yield?	“Severe yield reductions occur when crops are infested with golden dodder.”	Dept. of Ag. WA	H
20. Impact quality?	“Infested areas are often quarantined…” “Lucerne or hay containing golden dodder seeds or plant parts may not be sold or removed from the property.” Produce rejected for sale.	P & C (2001) Dept. of Ag. WA	H
21. Affect land value?	“Severe yield reductions occur when crops are infested with golden dodder.” “Infested areas are often quarantined, causing considerable financial loss and inconvenience.” Potential negative impact on agricultural production would seriously affect land value.	P & C (2001)	H
22. Change land use?	“When dodder is removed from agricultural land, the area must be sown to resistant plants, such as cereals or pasture grasses, and not resown to susceptible crops for at least 5 years.”	P & C (2001)	M
23. Increase harvest costs?	Not viable to harvest crop. No increase in harvest costs.		L
24. Disease host/vector?	“Dodders transmit diseases in certain crops.”	P & C (2001)	H