Plant-parasitic nematodes are ubiquitous in agricultural soils. In nematode suppres-sive soils, at the end of a growing season, only a very small fraction of the eggs that lie dormant, somewhat less than 10%, will fulfill their life-cycle and reproduce the next generation (Kerry and Crump 1977). This reduction in reproductive capacity of the plant-parasitic nematodes has been attributed to a whole diverse spectrum of microbial control agents such as Dactylella oviparasitica, Hirsutella rhossiliensis, Fusarium spp, Pochonia chlamydosporia or Trichoderma, and other groups of bacteria such as Bacillus spp., Pasteuria penetrans and Pseudomonas aureofaciens. Therefore, it is the phenomenon of nematode suppressive soils associated with many crops that has been the motivating force behind the research on biological control of nematodes (e.g. see Chap. 10). The goals of this research has been to understand the mechanisms of this phenomenon in order to develop environmentally benign strategies to manage these pests either through agronomic practices, or through the development of commercial products that can be applied. Biological control of plant-parasitic nematode pests would therefore seem, on the face of it, to be relatively straight forward and attainable. However, the reality has proven to be more difficult and if nematode suppression was easily understandable and applicable, biological control would already be a robust crop protection technology.
The wide range of different microbial entities associated with nematode suppression offer a spacious array of different approaches and control options. Each organism will have its advantages and disadvantages, for example candidates that can be cultured very easily in vitro have advantages over those that are obligate pathogens that cannot, and again when it comes to other aspects of development such as formulation, storage and application, each organism will have its advantages and disadvantages. To date, there are already a number of products on the market (Table 12.1) and even this small amount outnumbers the number of new commercial nematicides and there are other potential organisms that are being developed (Hallmann et al. 2009). Most biological control products for nema-todes so far exist as a liquid or wettable powder formulations applied in furrow or through drip irrigation systems and one of the major drawbacks to these inun-dative practices is the volume of soil needed to be treated in order to protect root systems. It is important to protect plants from nematodes while they are establishing themselves in the soil and it has been estimated that around 2,500 t/ha of soil in the upper 25 cm usually needs to be treated to obtain effective control (Sikora et al. 2008). It is therefore perhaps not surprising that biological control of nema-todes has concentrated on high value crops and niche markets, for example the development of EconemTM, a formulation of Pasteuria usage by Pasteuria Biosciences LLC, to control sting nematode (Belonolaimus longicaudatus) which is a problem on the greens of golf courses.
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