Incorporating spatial pattern of harmful organisms into crop loss models

Weeds, pests and pathogens (collectively, harmful organisms) tend to have patchy spatial patterns at the field scale. The idea that this patchiness may influence the way that harmful organisms compete with, or exploit, crop plants is not new. Recently, however, increasing economic and environmental pressures have led to a requirement for more accurate use of crop protection measures. This, in turn, requires more accurate predictions of populations of harmful organisms. Against this background, there have been attempts to develop a framework for the quantification of the effect of spatial pattern of harmful organisms on crop yield. There are two main elements of this framework: models of compensatory growth by healthy plants neighbouring affected ones; and models of intra-specific competition within the harmful organism population. Methods allowing the incorporation of these elements into models of crop loss to harmful organisms are reviewed. Thus far, practical implementation of crop loss models incorporating spatial pattern of harmful organisms has not been widespread. Further emphasis on field studies is likely to bc necessary before this situation changes.