Ennemis des cultures agricoles au Sahel

Most climate models predict an increase in temperatures across the Sahel, but there is significant uncertainty regarding the evolution of precipitation. On average, models suggest a slight increase in annual rainfall in the central Sahel and a decrease in the west. Climate change can also affect the onset of the rainy season and lead to an increase in extreme weather events. Furthermore, these changes can have an impact on the risks associated with insect pests and diseases affecting crops. The report "Agricultural Adaptation to Climate Change in the Sahel: Expected Impacts on Pests and Diseases Afflicting Selected Crops" documents the current prevalence and impact of diseases and insect pests on 16 major crops in the region. Academic publications have identified over 100 diseases and insects that currently affect these 16 crops. The report provides a detailed profile of each disease and insect pest, including the damage they cause, their mode of transmission, their general impacts, and the environmental conditions that influence their spread. While these environmental conditions are often linked to climate, other factors such as soil moisture, shade, wind, or other vectors also play a role. The report also identifies the consequences of intra-annual phenomena when possible. Additionally, the study projects the future conditions that may impact the different diseases and insect pests. Given the significant uncertainty regarding future precipitation, the study uses two simplified climate scenarios for 2025 – hot and humid, and hot and dry – to make preliminary projections about the potential effects of climate change on the risk factors of these pests and diseases. Non-climatic changes will also have consequences on the risks of pests and diseases in the Sahel. Farmers will likely adopt new techniques to manage pests and diseases, and adopt new varieties with different levels of resistance to these pests. The expansion to other regions may also influence these risks. The cotton plant is one of the fiber crops affected by insect pests in the Sahel. The cotton aphid, Aphis gossypii, is a significant pest of cotton crops. The aphid causes damage to the leaves, which can lead to yellowing, curling, and eventually, the leaves may drop. The aphid's saliva can also cause chlorosis and reduce sap flow, affecting plant development and health. The honeydew produced by the aphid can form a sticky film on the leaves, promoting the growth of sooty mold, which can further weaken the plant. The aphid can also transmit over 70 types of viruses, some of which can cause more damage than the aphid itself. The aphid's life cycle is influenced by environmental conditions. In temperate regions, A. gossypii is partially holocyclic, while in warmer regions, it reproduces asexually. The aphid is highly resistant to heat and can produce up to 60 generations per year in favorable conditions. Climate change can exacerbate the damage caused by the aphid, particularly in areas where the climate is already dry. The risk of aphid infestation is low in hot and humid conditions, but high in hot and dry conditions.