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Pest risk assessments for pests of quarantine concern

Pests of quarantine concern associated with table grapes from California to Western Australia were identified in the pest categorisation process (Appendix A). This chapter assesses the probability of the entry, establishment and spread of these pests and the associated potential economic, including environmental, consequences.

This review builds on previous policy for table grapes from California to the rest of Australia (AQIS 1999; AQIS 2000a; AQIS 2000b; Biosecurity Australia 2002; Biosecurity Australia 2003; Biosecurity Australia 2006).

Pest categorisation identified 14 pests of quarantine concern associated with table grapes from California to Western Australia that do not have risk management measures in the existing policy for Californian table grapes to other Australian states and territories. Table 4 .11 identifies these pests, and full details of the pest categorisation are given in Appendix A. Additional pest data are given in Appendix B.

No pest risk assessments were conducted for those pests with risk management measures already in place under the existing policy for Californian table grapes to the rest of Australia. Any existing measures for those pests will be applied to imports to Western Australia.

Assessments of risks associated with the 14 pests of quarantine concern are presented in this chapter. Pests are listed or grouped according to their taxonomic classification, consistent with Appendix A and Appendix B.

For each pest, the PRA area is defined as the state of Western Australia. The likelihood ratings given for entry, establishment and spread and the associated consequences are for Western Australia.

Pest risk assessments were completed to determine whether the risk posed by each pest exceeds Australia’s ALOP and thus whether biosecurity measures are required to manage the risk.

For some of the 14 pests identified, pest risk assessments have already been completed for other commodities or other source countries. For these pests, the likelihood of importation and/or the likelihood of distribution may be reassessed due to the differences in the commodity and growing region assessed. The likelihood of establishment and spread and the consequences the pests may cause have been based on the outcomes from the previous assessment. If previous policy has been considered, this will be stated in the introduction for the pest.

Table 4.11 – Pests of quarantine concern for table grapes from California identified in the draft review but which do not have risk management measures in the existing policy for Californian table grapes into Australia

Pest	Common name
Harmonia axyridis	Harlequin ladybug
Lygus hesperus	Western plant bug
Lygus lineolaris	Tarnished plant bug
Parthenolecanium corni	European fruit lecanium scale
Pseudococcus calceolariae	Citrophilus mealybug
Marmara gulosa	Citrus peel miner
Phomopsis viticola	Phomopsis cane and leaf spot
Strawberry latent ringspot virus
Grapevine fanleaf virus
Tomato ringspot virus
Grapevine yellow speckle viroid 1
Grapevine yellow speckle viroid 2
Hop stunt viroid
Citrus exocortis viroid

In the following pest risk assessments DAFF considered several matters that were common for most pests and pathogens. These included the possibility that:

• 
  imported Californian table grapes will contain seeds and that those seeds may germinate
  
• 
  consumers will discard Californian table grapes in environments suitable for pest or pathogen distribution to a host or for seed germination in the case of seed transmitted pathogens (including household compost)
  
• 
  a seedling from a Californian table grape seed will survive and establish and that a pathogen of quarantine concern may infect that seedling.
  

California exports both seeded and seedless table grape varieties to Australia. DAFF assumes that some viable grapevine seed from fruit consumed by the public will be discarded into natural and unmanaged environments as well as household composts. However, out of the top fourteen varieties of table grapes grown in California, only one variety, Red Globe, has seeded berries (California table grape Commission 2012d). Red Globe represents the third top variety by volume shipped from California (Anonymous 2011). As such, some seeded table grapes are expected to be exported from California to Australia, however the majority of table grapes are likely to be seedless varieties which have no risk of seed transmission of pathogens.

In general, grapevines are grown from vegetatively propagated cuttings that are grafted onto rootstock or, less commonly, self-rooted (Zohary 1996). Vineyards are not established using vines propagated from seed as these vines are likely to produce inferior berries and are unlikely to be true to type after genetic segregation (Zohary 1996). This aspect of grapevine propagation, along with the relatively long time taken to grow a productive vine from seed, will likely deter members of the public from deliberately growing grapevines from the seed of imported fruit (Olmo 1976). The wide availability of grafted vines will also reduce the incentive to grow vines from seed.

The proportion of grapevine seed that germinates depends on the cultivar, seed maturity, storage, stratification and planting conditions (Doijode 2001). Most grapevine seed is dormant and will not germinate unless it has been stratified. Successful stratification is usually achieved by storing seed at 0–5 °C for two months or longer (Ellis et al. 1985; Doijode 2001). Low germination rates of seed from fresh untreated berries or room temperature stored seed has been reported in the literature, although longer storage periods after ripening positively correlated with germination rates (Scott and Ink 1950; Singh 1961).

The timing of exports of Californian table grapes to Australia is another important consideration because discarded seed may be stratified by low temperatures in winter. Although table grapes are harvested in California from May to January (Pollack and Perez 2007), exports to Australia occur between June and November. This coincides with winter, when seed are more likely to stratify naturally in low temperatures (in some parts of Australia) and spring, when conditions are more favourable for growth of seedlings.

Germination of some untreated seed is reported to be slow and some seedlings grown from untreated seed are stunted (Scott and Ink 1950; Mamarov et al. 1958). However, grapevine seedlings sometimes occur in vineyards (Office of the Gene Technology Regulator 2003). In Europe, volunteer grapevines grow as weeds in small numbers. Most of these weedy vines are probably rootstocks that have escaped vegetatively or have grown from seed, although some may be escaped cultivars of grapevine that have grown from seed (Zohary 1996; Arrigo and Arnold 2007; Ocete et al. 2008).

Grapevine is not a common weed in Australia (Office of the Gene Technology Regulator 2003), but there are reports of grapevine growing as a weed on roadsides and in disturbed areas in NSW, Victoria and Western Australia (Richardson et al. 2006) and vines have been found near established vineyards and water-courses (Conn 2010). Grapevine has been recorded as naturalised in Western Australia (Conn 2010) and thus climatic conditions are suitable for the establishment of wild grapevines in some parts of Western Australia.

There is some risk of consumers discarding grape seed into household compost piles. One study which investigated food-related behaviours of Australians found that half of respondents composted their food waste often (Lea and Worsley 2008), but the proportion of grape seeds that are discarded as compost is not known. If conditions were right, grapevine seed could germinate, but as discussed, untreated seed has variable rates of germination. Given that most Californian table grapes are seedless, the risk of a Californian table grape seed germinating in a household compost pile is low.

The likelihood that table grape waste may be discarded close to other suitable hosts for the pests and pathogens concerned was also considered. Most households in Australia do not grow table grapes; the highest proportion occurs in Western Australia, South Australia and the Australian Capital Territory with about 1 in 10 private dwellings growing grapes (Cross and Taylor 1996). Other suitable hosts may be present in backyards, but this depends on the pest or pathogen considered and is discussed, when relevant, in the pest risk assessments below.

Given the available evidence, DAFF considers that some waste from imported table grapes will be disposed of in household compost or other natural or unmanaged environments. There is a low likelihood that this will be adjacent to a suitable host for the quarantine pests and pathogens considered. The biology of each pest and pathogen will determine how close a suitable host needs to be for distribution to occur. Also, a very small proportion of seed from imported table grapes may germinate when table grapes are discarded in compost or somewhere such as on a road side. A seedling may establish given that grapevines are known to grow wild in some parts of Australia. But given the barriers to successful seed germination discussed above, and the fact that only some Californian table grapes contain seeds, this would not be likely to occur.