| Popis: |
Crop losses are influenced by several factors including the pathogenicity of the species of nematode involved, the nematode population density at planting, the susceptibility and tolerance of the host, and a range of environmental factors (Trudgill and Phillips 1997). Because of this, available models only estimate yield losses as proportions of the nematode-free yield. Estimating threshold levels further involves various economic calculations. Consequently, predicting yield losses and calculating economic thresholds for most nematode/crop problems is not yet possible. What is needed is more field-based information on the relationship between nematode population densities and crop performance, and various approaches to obtaining such data are described. Measuring the population density, especially of Meloidogyne species, is a major problem which needs addressing. Better loss estimates are needed for most crops, but good estimates are costly in time and money. Detailed surveys and accurate damage threshold relationships are essential for strengthening expert opinion for generating loss estimates, which is currently the most feasible way to approach this vast and complex topic. Costs of nematode management practices and quarantine and regulatory penalties also should be included more often in generating loss information in the future. |
