In spite of the impact of multilateral trade agreements and phytosanitary regulations, interceptions of regulated nematodes do occur, such as on infested container-grown plants or in potato tubers. On such occasions the consignment may be destroyed, returned to origin, diverted to a different end use (such as consumption), or diverted to another country to prevent the spread of pests, as invariably no effective treatment or other control exists. A few cultural methods may be employed where the nematode species have been identified as low risk. For example, root washing may be an option in the case of ectoparasitic species, but this may damage the plants.
It is difficult to eradicate a nematode species of particular economic importance when an outbreak has occurred on a crop or range of crops. Suppression (i.e. the application of phytosanitary measures to reduce the pest population) or containment (i.e. the application of phytosanitary measures in and around an infested area to prevent spread of a pest) may be more feasible and such campaigns may be cost- effective. In particular they set an example to the agricultural and horticultural indus- tries of the principles of pest control. On occasions, the benefits may be difficult to justify in monetary terms but there may be other environmental concerns or advan- tages to the trade in general. Cost:benefit analyses rely heavily on the availability and
quality of data but the problem with most nematode species is that little is known about their economic effects.
It remains in national and international interests to restrict the spread of harmful organisms and so minimize their impact on trade, industries and the environment.
The following examples explain how certain nematode species are being suppressed and contained by three different phytosanitary programmes and the associated cost:benefits.
12.9.1. Phytosanitary suppression programmes forRadopholus similis in the USA
The programme to suppress and prevent further spread of the citrus race of R. similis in Florida is very important because of the phytosanitary legislation involving this nematode in many countries worldwide (see Section 12.5). In the early 1950s, a seri- ous decline of citrus orchards appeared, primarily in central Florida. In 1953, it was discovered that R. similis was the causal agent of the problem, known as spreading decline. Nematode-infested propagative material from Florida nurseries infested with bothR. similis and T. semipenetrans had been disseminated into Florida’s new and old citrus-growing areas where these nematodes were not native.
The management strategies implemented in the affected areas included surveys to delimit these infested areas, tree removal followed by soil chemical treatment (nick- named ‘push and treat’) and isolation of orchards with chemical-treated buffer zones (barriers) around the infested areas. Concomitantly with the ‘push and treat’ pro- gramme, a citrus nursery certification programme was established, which required nursery stock to be grown under rigorous sanitation programmes to ensure that com- mercial citrus seedlings were free of R. similis and T. semipenetrans.
The combination of the initial suppression programme (push and treat), the bar- rier programme to isolate the infested orchards and the citrus nursery certification resulted in a reduction of nematode-infested hectares from 3798 ha in the 1950s to 1538 ha in 1984. The number of citrus nurseries infested by R. similis declined drasti- cally from 278 in the 1950s to none from 1970 until now. Recent studies indicate that R. similis would have spread at least to an additional 18,000 ha without implementa- tion of the phytosanitary programmes. The benefit of preventing the spread of R. similis to such an area of land potentially susceptible to the spreading decline was estimated at about US$1.4 billion (€1.05 billion) for a 35-year period. The cost of the suppression programmes was about US$100 million (€75.2 million) or 7% of the benefit value (Lehman, 2004).
The eradication approach of ‘push and treat’ was discontinued in the 1980s because of the serious environmental consequences resulting from the excessive use of fumigant nematicides. The citrus nursery nematode programme, which was initi- ated 50 years ago, has continued and the benefits growers received in 2000 was estimated to be US$17 million (€12.8 million) for R. similis and US$33 million (€24.8 million) for T. semipenetrans. The cost to the citrus industry of implementing the citrus certification programme was US$75,000 (€56,390) (Lehman, 2004).
The direct damage that R. similis causes to the citrus industry in Florida has had a rippling indirect and adverse effect on the ornamental industry of Florida; unfortu- nately, both the banana and citrus races of R. similis (see Chapter 5) are able to infest
and reproduce on many ornamentals in many different families including plants in the Araceae, Laurantaceae, Marantaceae, Musaceae (which includes banana), Palmae and Strelitziceae, although the banana race does not attack citrus plants (Rutaceae).
The absence of reliable morphological and molecular identification tools to distin- guish between the races has resulted in a ban on all infected plant shipments from Florida by all the citrus-producing states in the USA and by many countries in order to protect their banana, citrus and ornamental interests. For the same reason this ban has also applied to other tropical states such as Hawaii and other countries (regard- less of the race they have).
A financial disaster for the ornamental industry in Florida has been averted by the adoption of a nematode certification programme in the ornamental industry similar to that described earlier for citrus nurseries. Florida ornamental nurseries implement nematode eradication programmes using strict phytosanitary practices in order to export ornamentals to national and international markets. These pro- grammes include the use of approved growing media such as sterile peat, clean sand, sawdust or wood shavings, or biologically inert fillers such as perlite or vermiculite.
Clean propagative material is grown in these media and kept in clean containers not in contact with the ground, which may be inhabited by prohibited pests and patho- gens. Other common sanitation requirements include clean irrigation water, weed control, appropriate sloping of the ground to avoid flooding of the nurseries, and construction of cement slabs or benches to protect the containers and growing media. Nurseries are periodically (usually annually) inspected and sampled by offic- ers of the Florida Department of Agriculture and Consumer Services, and if prohib- ited nematodes are found the nursery is suspended from shipping plants until the production line is clean. Such phytosanitary programmes are expensive and are justi- fied only by the high market values of ornamentals (more than US$1 billion (€0.75 billion) in Florida).
12.9.2. Nematode phytosanitary exclusion programme for cotton and vegetables
As in some other states of the USA, plant health officials in California conduct inspec- tions at the state’s border stations to verify that agricultural commodities are free from its state-regulated pests, including nematode pests. Here the cost of excluding non- indigenous nematode pests has been estimated to be 3% of the potential crop loss value these nematodes would cause if accidentally introduced into the state. For the year 2000, this potential crop loss value was estimated to be US$600 million (€450 million).
In particular, the benefits of excluding the reniform nematode, R. reniformis, from the California cotton industry (valued at US$1 billion (€0.75 billion)) are estimated at US$7.2 million (€5.4 million). These benefits were calculated by assuming similar crop losses (7%) to those that have occurred in other US states. Similar benefits are achieved for the California melon and vegetable industry, valued at US$4 billion (€3 billion), because this pest causes 10% crop losses to cantaloupe and snap bean elsewhere. The annual cost of the certification programmes implemented in Florida to exclude California’s state-regulated nematodes from California is US$100,000 (€75,190), which represents only about 1.3% of the losses that the California cotton industry would expect annually if R. reniformis became established in their cotton fields.
12.9.3. Eradication programmes for Globodera rostochiensis andG. pallida in the USA
The first regulatory measures against G. rostochiensis in New York were imple- mented at state level in 1944. Stringent phytosanitary programmes were established by the Golden Nematode Act, promulgated in the USA in 1948; these have prevented the spread of G. rostochiensis within and outside the state of New York since that time. In 2012, APHIS removed some of the regulated areas in this state. The use of seed potatoes originating from states where G. rostochiensis has not been found has been critical in preventing the spread of this nematode in the USA. An outbreak of G. pallida occurred in 2006 in Idaho, where exclusionary measures were also enacted at a cost of US$58.8 million (€44.2 million) from 2006 to 2012 (Skantar et al., 2007;
Anon, 2011; and data kindly provided by Jonathan M. Jones, National Program Manager, USDA-APHIS-PPQ, 2012). Considering that PCN species can suppress potato yields by more than 10%, the benefits of excluding these nematodes from potato-growing areas in the USA are estimated to be US$300 million (€225 million) annually at 1995 values. These benefits are far greater than the US$445,000 costs (€334,595) (1996 data) required for preventing the spread of G. rostochiensis in and outside New York (Dwinell and Lehman, 2004).