Global climate change: Modelling the potential responses of agro-ecosystems with special reference to crop protection

Pests and diseases reduce yields to lower levels than those that could have been potentially obtained, given the restrictions of climate, nutrients and crop varieties. Climatic change not only affects the potential yield levels, but it may also modify the effects of pests and diseases. Modelling can serve as a tool to integrate these processes, ranging from simple removal of plant material to subtle toxic and hormonal effects. Modelling can help to quantify different modes of action such as on photosynthesis, root activity, assimilate partitioning, morphology, and their interactions. As to climatic change, little is known about pests, diseases and weeds. If climatic change causes a gradual shift of agricultural regions, crops and their associated pests, diseases and weeds will migrate together, though at different rates maybe. To a limited extent, new outbreaks can be foreseen given the changed environmental conditions. Methodology is available, and some interesting results are on record. Specific changes such as an increase in the CO2 content in the air and in UV radiation are not likely to have large effects. Increasing atmospheric CO2 reduces crop nitrogen content, which may retard many pests and diseases, and change the composition of the weed flora which accompanies crops. Some cautionary remarks are made to avoid jumping to conclusions.