Correlations between historical climate data and incidents of common bunt in Spanish wheat, 1755-1801

From 1755 to 1801 in Spain, many articles and reports were written about common bunt, a seed-borne plague that was difficult to control at the time. The objective of the study is to better understand this plague and the relationship between historical rainfall indexes and years of higher reported outbreaks. We compared documentary sources on extreme rain events and annual series of wheat prices in four locations (Murcia, Seville, Toledo, and Zamora) with data from articles about the bunt plague. Increased severity of common bunt in wheat coincided with a concentration of such events, during a period of severe climatic irregularity known as the Maldà Anomaly. However, the cause-and-effect relationship for proxies of historical weather, price volatility and bunt plague was only significant in Seville. A complementary factor that explains the abundance of literature was access to agricultural articles and books from France, where the common bunt also existed. The first experiments to understand the plague and how to control it were performed there. These events are framed in the Spanish Enlightenment and early physiocratic ideas advocating the importance of agriculture in maintaining the wealth of a country.