Management of powdery mildew and behaviour of late blight under different irrigation configurations in organic tomato

Abstract Disease management options for organic tomato growers are limited. However, the dry winter in the Brazilian Mid-West is unfavourable to most foliar diseases, and is considered ideal for organic agriculture. We report on powdery mildew (PM) disease progress in organic tomato, under different irrigation configurations. The progress of late blight is also addressed. Staked, fresh-market tomatoes were grown in 2009 and 2010, under drip (DRP); furrow (FUR); microsprinkler (MIC); and overhead (OVH) systems. DRP, MIC and OVH were managed to maintain either high or moderate levels of soil moisture. FUR was managed to maintain moderate soil moisture only. In 2011, three treatments were added to study the extent of PM control with microsprinklers: MIC above plant canopy (MIC AP ); a DRP-MIC combination, above plant canopy, alternately used (DRP-MIC A ); and a DRP-MIC combination, where microsprinkler was applied as a PM control measure only (DRP-MIC C ). Irrigation systems that maximized leaf wetting provided the best PM control, reduced maximum disease severity (Y max ); severity at halfway point of the epidemic time course (Y 50 ); area under disease progress curve (AUDPC); and disease progress rate (r). Overall, the intensity of late blight was much lower than PM, and no blight was detected in 2010. The DRP and FUR systems consistently hampered foliar diseases development in 2009/2011. PM is significantly reduced by irrigation management while late blight is a lesser disease in the Brazilian Mid-West winter season. Therefore, irrigation is a tool to control diseases in organic tomato, and likely, other cropping systems.