Improve Pests and Disease Models

In natural ecosystems, and also in cultivated or forest ecosystems, climatic change is capable of disturbing the balance between the species, whether they are plant and/or animal, both in terms of the individual and the population (Loreau et al., 2001). These changes will also modify the development of weeds, diseases and parasites among crops, as well as their area of distribution. The effect of climatic changes on the development of pests and diseases could manifest itself in two main processes:

Uncultivated areas HI Sams lOdays) very earty (-iSOilays) U Lale(>10day&) early (<10 deys) | Very lute 20 days)

~] Uncultivated areas j Same

■j V«ry low< - 3DO lo IKHjiruj) U Higtift 100 w + 300 Kg/ha)

_ t-ow [<■ 3Q0 kg/ha) ■ Very High (> 300 kfjltia)

Figure 6. (a) A map of millet successful sowing dates differences between 1998 and an average 1961-1990 (from Samba et al., 2001). (b) A map of millet yields differences between 1998 and an average 1961-1990 (from Samba et al., 2001).

~] Uncultivated areas j Same

■j V«ry low< - 3DO lo IKHjiruj) U Higtift 100 w + 300 Kg/ha)

_ t-ow [<■ 3Q0 kg/ha) ■ Very High (> 300 kfjltia)

Figure 6. (a) A map of millet successful sowing dates differences between 1998 and an average 1961-1990 (from Samba et al., 2001). (b) A map of millet yields differences between 1998 and an average 1961-1990 (from Samba et al., 2001).

• A direct effect on the biological cycle of the parasites. In the event of climatic warming, certain thermophilic parasites would find even more favourable conditions in their current area of distribution and could extend this to as yet little affected areas where their hosts are present.

• An effect on host-parasite interaction and, more globally, on the complex interactions which exist in the trophic networks and which may modify the effectiveness of control using biological agents. Climatic changes will modify the development of crops, and hence might affect the phenology or resistance of plants. The synchronisation between host and parasite could thus be markedly disrupted.

Several approaches are possible in trying to estimate the impact of climatic changes on plant diseases. Using climatic concordance models, similarities between the future climate in a given area and the current climate in another area can be used to forecast sanitary risks by analogy. We can also establish predictions based on previously established empirical relations between the impact of parasites and climatic variables (Coakley and Scherm, 1996). But, faced with the complexity of the problem, it is much more efficient to use epidemiological models: epidemiological development is described in the form of a functional model where each biological process and its integration are linked to climatic parameters (Goudri-aan and Zadoks, 1995). The objective is then to couple these models to crop simulation models. However, creating these models necessitates the acquisition of various observed data and knowledge acquired by experimenting on the disease. At the present time, very few of these models are available and it is absolutely essential that progress is made in this area.

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