1 Appendix 2 Appendix 2. Suitability of Gargaphia decoris as a biocontrol agent for woolly nightshade in New Zealand 1. The woolly nightshade problem in New Zealand 2. Scope for biological control in New Zealand 3. Biological control against woolly nightshade in South Africa 4. Determination of the host range of Gargaphia decoris 5. Post-release effects on woolly nightshade in South Africa 6. References 1. The woolly nightshade problem in New Zealand Distribution The native range of Solanum mauritianum (woolly nightshade) is Argentina, Uruguay, Paraguay and southern Brazil. It is naturalised widely in the Pacific, Indian Ocean islands, India and several southern African countries, and is considered to be an agricultural and environmental weed in New Zealand, South Africa and Australia (ISSG 2006). It has been naturalised in New Zealand since about 1880. It is now abundant in all areas from Taupo northward, but is still uncommon in the Gisborne, Wellington and Tasman regions. It is present in Tasman and Nelson but is not yet regarded as a weed in the remainder of the South Island. Woolly nightshade thrives throughout the northern parts of the Waikato Region and can be common in other areas. Dense stands occur in the Port Waikato area and on the Coromandel Peninsula. Plants inhabit bush margins, gardens, roadsides, ungrazed wasteland areas, wetlands, and banks of streams. A consistent theme of consultation (Appendix 1) was that woolly nightshade has not yet occupied its available habitat either latitudinally or within its existing range. Woolly nightshade appears to be extending its range southwards and becoming more common (Rahman & Popay 2001). Stanley (2003) records 54,000 of woolly nightshade in the Bay of Plenty Region, but states that 270,000 ha are at risk of invasion. It occupies 245,000 ha in the Auckland Region, but its available habitat is thought to be 345,000 ha (J. Craw ARC pers. comm., Appendix 1). In total, woolly nightshade is thought to occupy 453,000 ha of the Auckland, Waikato and Bay of Plenty regions (Appendix 1). Biology The biology and ecology of woolly nightshade is well reviewed by Stanley (2003). It is a lowland tree that grows to around 10 m tall, to a stem diameter of 15 cm. Leaves are ovate and entire, 10–25 cm long and 5–10 cm wide, green above and whitish below, and covered with hairs. Leaves have a pungent smell redolent of kerosene. It is moderately tolerant to frost, shade and drought, but requires medium to high soil fertility. Berries are globose, dull yellow, and approximately 1 cm in diameter. Each fruit contains many seeds, and a single plant can produce up to 10 000 seeds annually. Most fruits fall beneath the tree, but the seeds of woolly nightshade are thought to be dispersed widely by birds and possums. Silvereyes and kereru (Hemiphaga novaeseelandiae) have been observed feeding on its fruit (in Stanley 2003), and it seems likely that exotic species such as blackbirds would also carry seeds. A pilot 2 Appendix 2 study by Stanley (2003) suggested that seeds remain viable in the soil for only a few years, but this varies between sites, and longevity may be long at some sites. Seedlings established in summer can bear flowers by autumn (NZPCN 2008). Woolly nightshade tolerates moderate shade, moderate drought (once established) and moderate frost to –5oC (Stanley 2003). Pest characteristics Woolly nightshade is said to be poisonous, although reported incidences of actual poisoning in New Zealand are very difficult to find. Stanley (2003) reviews this evidence. The dust from the leaf hairs causes respiratory problems if exposure is prolonged, and handling the plants may cause skin irritation and nausea. The green berries contain toxins that could be poisonous, especially to children, although such poisonings have not been recorded. Woolly nightshade is an aggressively invasive and very fast growing plant. Most fruits fall beneath the tree, but plants fruit prolifically from the first year of establishment and viable seed is spread widely by birds. Once a seed source has established, seedlings from it can therefore establish over a wide area. Seedlings establish very quickly and can soon dominate poorly managed and neglected land. In New Zealand it seldom establishes in dense vegetation, but areas particularly at risk include native forest margins, scrub and shrubland areas including prime sites for native forest regeneration, amenity areas such as reserves, shelterbelts and farm woodlots, hill country grazing land, young pine plantations, woodlots, shelterbelts, waste spaces and open areas around urban gardens. Dense stands can overtake pasture, especially in hill country, and impede livestock movement. Woolly nightshade can quickly establish large, dominant stands of plants beneath which little else will grow, impacting plants and animals, and changing ecosystem structure. Invertebrate communities can be modified (in Stanley 2003). It has been observed that dense woolly nightshade infestations commonly lack understorey plants. This may be because of allelopathic effects (Florentine & Westbrook 2003; van den Bosch et al. 2004), or simply because shading from the large leaves of woolly nightshade preclude successful germination of seedlings. Whatever the reason, while a continuous canopy of woolly nightshade exists, no regeneration of native vegetation can occur in forest margins and gaps. Woolly nightshade produces large numbers of seeds, which have 95% viability. Three-year-old plants have been recorded bearing 10 000 seeds. Seed is spread by birds, but most falls close to the parent. Although woolly nightshade is relatively short lived, the seed bank ensures that woolly nightshade has a strong tendency to replace itself (Bruce Clarkson, pers. comm.). Where it becomes a dominant land cover, the productivity of the land may be severely reduced, and cultural and traditional values associated with a significant area may also be damaged. Affected parties include private land occupiers, groups responsible for managing significant areas, reserves and roadsides and the general community, which may access significant areas for recreational activities. Current regulatory requirements It is illegal to sell, propagate, or distribute any parts of woolly nightshade in New Zealand (NPPA 2008). Regional Pest Management Strategies (RPMS) govern how woolly nightshade management is conducted, and strategies vary between the regions in which it grows. 3 Appendix 2 For example, it is not listed in the pest management strategy for Tasman–Nelson at all, and while woolly nightshade is abundant in Taranaki, the regional council has no rule requiring its destruction; any control is voluntary. Greater Wellington Regional Council ensures that woolly nightshade is totally controlled at all known sites with a view to eventual eradication from the region. It is currently limited to 14 sites, 12 of which have been inactive for several years. Eradication of woolly nightshade from this region is possible (Greater Wellington Regional Council 2008). The weed has limited distribution in Gisborne, and eventual eradication is planned there also. Currently it is landholders’ responsibility to control all woolly nightshade plants on their land. Some regional councils require mandatory removal of all plants from properties at the expense of the occupier, or participation in organised programmes (Hawke’s Bay, Bay of Plenty, Manawatu–Wanganui, parts of Waikato, Auckland and Northland,), while others require clearance from boundaries only (parts of Waikato, Auckland and Northland). Requirements under the RPMSs bind corporate and crown land managers (including DoC and forestry companies) as well as individual occupiers. Table 1. Rules for management of woolly nightshade in regional pest management strategies, and direct costs borne by regional councils Region Treatment rule Direct annual council expenditure Northland Assistance with community $10,000 (estimate) projects Auckland 1. Occupier control, 2. boundary $260,000 clearance Waikato Mandatory control by occupier $39,600 Bay of Plenty Progressive control by occupiers $171,488 Horizons Mandatory control by occupier $16,360 Hawke’s Bay Eradication by council $20,000 Gisborne Eradication by occupier No estimate Taranaki Voluntary control by occupier No estimate Wellington Eradication by council $6,340 Tasman/Nelson Not designated pest $4,500 Current control methods Details of control methods can be found at http://www.ew.govt.nz/Environmental- information/Plant-and-animal-pests/Plant-pests/Woolly-nightshade/ Where infestations are accessible, and resources allow, woolly nightshade can be successfully controlled by conventional means. Ground disturbance often leads to seedling germination. Plants up to 60 cm tall can be pulled. Taller plants can be cut, and the stumps treated to minimise regrowth. Stanley (2003) also reviews control techniques. The benefits and costs of woolly nightshade Consultation with regional councils and tāngata whenua indicates that woolly nightshade has no known beneficial attributes or value (Appendix 1). 4 Appendix 2 Woolly nightshade causes non-monetary adverse effects to ecological values in native ecosystems, and to societal well-being in urban environments. It reduces the value of production in pastoral agriculture and forestry, and imposes monetary costs for control. Woolly nightshade has an Owens score of 24 for ‘biological success’ and ‘effect on ecosystems’ (C. West DoC pers. comm.), and Timmins and MacKenzie (1995) record it as a plant of