Once nematodes are established in the soil their eradication is very difficult. The objective of the management strategies is to increase crop yield by reducing the nematode population on soil and, consequently, limiting the damage to a level economically acceptable (Coyne et al., 2009).
In the past century, nematicides were used to minimize crop losses caused by RKN.
However, the adverse impacts on the environment and human health have reduced their use resulting on the elimination of methyl bromide and others compounds from the market. Nevertheless, nematicides continue to be an alternative for nematode control as part of integrated management programmes, and currently approximately 250,000 t of active compounds are used each year in the world to control nematodes in soil (Haydock et al., 2006). Furthermore, for economically important high-value crops, nematicides are the only alternative, often used to prevent infection of established plants. It is a fast way to nematode management though normally implies a re-treatment each year if plants grown are susceptible to RKN (Karsen & Moens, 2006).
The increasing concern of producers and consumers about the risks posed by these chemicals has stimulated research to the development of “natural” nematicides, derived from plant extracts and microorganisms. Non-chemical pest management alternatives are environmentally friendly and cause no risks to humans or animals (Haydock et al., 2006).
Root-knot nematodes move only a few meters annually in the soil, but they can be disseminated to different regions through human activities, transport of infected plants and soil adhering to farm implements and in water irrigation. National and international quarantine measures were established to decrease the risk of spread and introduction of a new species into a region where it does not exist (Moens et al., 2009). The use and transport of clean, healthy, nematode-free planting material is a prerequisite for limiting spread of nematodes. For example, M. chitwoodi and M. fallax, two economically important species, due to the high impact on potato, tomato and carrots production and restricted distribution have been included in the list of quarantine species. This status implies an inspection of symptoms of the host plants in the field and in potato tubers or carrots, in order to increase the probability of detection, before they are certificated and authorized to transport (EPPO/OEPP, 2004).
Crop rotation and growing of resistant cultivars are ecologically healthy, effective and widely used strategies for nematode control. In crop rotation fallow periods or non-hosts, resistant or immune plants to RKN species are rotated with susceptible crops, this approach requires the knowledge about the host status of a large number of plants. For some species with a narrow host range is easy but for other important species, with a wide host range, this strategy has its limitation. Also, in soils with more than one Meloidogyne species, this approach can lead to a selection and increase the population of particular species as a non-host plant for one RKN species may be a host to another species present in the same field. Nematode management by crop rotation should be performed locally and depend on the nematode species found in the field.
Presence of different pests and diseases, soil fertility, presence of weeds, that can be alternative hosts and serve as nematode reservoirs, and the absence/presence of market for the new crop are other parameters to take into account when devising an integrated nematode management strategy (Whitehead, 1997; Halbrendt & La Mondia, 2004). On periods of fallow, the nematode population decrease in the soil due to the lack of susceptible plants and during this period of time there is an increase of the natural flora of non-host plants. Maintaining soil without vegetation is disadvantageous, because it increases the possibility of erosion and loss of soil fertility (Halbrendt & La Mondia, 2004).
The expression of plant resistance is characterized by suppression of nematode development and reproduction, which include programmed cell death and tissue necrosis around the nematode head. In some host plants, as carrot, clover, coffee,
common bean, cotton, cowpea, grape, groundnut, lima bean, lucerne, pepper, potato, Prunus, soybean, sugar beet, sweet potato, tobacco, tomato and wheat, multiple resistance genes have been identified but only some are available in cultivated crops. In wild tomato, for example, nine genes that confer resistance to Meloidogyne spp. were identified, but only the Mi-1 gene is available in cultivated tomato (Williamson & Roberts, 2009). Some natural and laboratory-selected Meloidogyne isolates, by repeated exposure, can overcome nematode resistance genes and constitute a threat to this strategy of control. Some isolates of M. arenaria, M. incognita and M. javanica, one isolate of M. chitwoodi and species such as M. enterolobii (=M. mayaguensis), M. exigua, M. floridensis and M. hapla can overcome Mi-mediated resistance (Roberts et al., 1990; Kaloshian et al., 1996; Brown et al., 1997;
Williamson, 1999; Ornat et al., 2001; Molinari & Caradonna, 2003; Karajeh et al., 2005;
Tzortzakakis et al., 2005; Brito et al., 2007; Silva et al., 2008). Incorporation of resistant plants in rotation practices can help to preserve the durability of resistance in the field preventing the selection of virulent nematode populations, reduce the population of RKN and increase the yield of the next crop (Rich & Olson, 2004; Verdejo-Lucas &
Sorribas, 2008; Talavera et al., 2009).
Combining the use of resistant cultivars and crop rotation can contribute to control RKN and provide a cost-effective and environmentally safe method for managing plant-parasitic nematodes (Roberts, 1992). Others practice more restrictive and specialized have been used: time of planting and harvesting, removal or destruction of infected host plants, flooding, biofumigation, solarization, heat treatment, steaming, use of allelopathic plants that release nematicidal compounds into the rhizosphere, trap crops, green manure and soil amendments and biological control with nematophagous fungi and bacteria. All these practices of nematode management, when available, should be considered as strategies to be use in an integrated management programme (Sasser, 1971; Halbrendt & La Mondia, 2004).