Dynamics of common bean web blight epidemics and grain yields in different tillage systems

The effects of tillage systems on the dynamics of web blight caused by Thanatephorus cucumeris and yield of common bean ( Phaseolus vulgaris ) cv. Pérola were studied in three field experiments during the planting seasons of 2004/2005, 2005/2006 and 2006/2007. Congo grass ( Urochloa ruziziensis ) was managed in a naturally infested field to establish the following cropping systems: no-till (NT), minimum-tillage (MT) (disking with partially incorporated straw); and conventional tillage (CT) (residues burial by soil plowing). The area under disease progress curves (AUDPCs) and the disease progress rates were generally low in the NT system during the three cropping seasons, most likely due to the benefits of grass mulching. In general, AUDPC values were higher in the 2005/2006 compared to the other seasons due to more uniform rainfall distribution during the crop cycle. Bean yield was highest in CT despite a higher the high AUDPC, probably due to immobilization of nutrients in the soil after herbicide-burning of U. ruziziensis . An additional study conducted in 2006/2007 showed that distribution of 2 to 10 t. ha −1 of U. ruziziensis straw over bare soil increased average yield by 29.9 %, while disease severity was reduced by 31.1 %, in comparison to control plots with no mulch.