Responding to Late Blight Disease Pressure and Fungicide Resistance Using Multiple Fungicide Active Ingredients and Different Spraying Regimes in Uganda

Abstract

Late blight (<i>Phytophthora infestans</i>) is one of the major diseases of economic importance limiting potato production in Uganda and causing yield losses of 40-60%. The emergence of more aggressive late blight pathotypes that are more difficult to control with ability to overcome host resistance or resist fungicide active ingredients has been noted in Uganda. Therefore, this study was carried out to identify suitable fungicides and spray regime for the effective management of late blight pathotypes on susceptible potato varieties in Uganda. Different fungicides that known to control late blight include Consento (Fenamidone 6.7% w/w + Propamacarb hydrochroride 93.6% w/w), Infinito (Propamacarb (55.3% w/w + Fluopicollide (5.53% w/w), Mancozeb (Dithiocarbamate 800g/kg), Agrolaxzyl (Metalaxyl 80 g/kg + Mancozeb 640 g/kg WP) were acquired from Bayer Crop Sciences and agro-inputs dealers in Uganda and tested for effective management of late blight on susceptible potato varieties in four different sites for two seasons (2015B and 2016A) using randomized complete block design (RCBD). Three (3) spraying regimes were tested and included; Bayer Crop Sciences recommended spray regime, current Uganda’s recommended spray regime, Hybrid (blend of Uganda’s recommended spray regime and Bayer recommendation) and no spray as control. Data on late blight disease severity was measured as percentage plant area affected (PLAA) and this was converted in to area under disease progress curve (AUDPC). The results showed that area under disease progress curve (AUDPC) ranged from 357-763 for the 3 different spray regimes while for the control (No spray), it ranged from 1895-2231. The late blight disease severity varied across sites and seasons, with Kalegyere site recording highest disease pressure in season 1 while Buginyanya had highest disease severity in season 2. Lowest disease pressure was registered with Bayer Crop Sciences based spray regime in season 1, while in season 2, hybrid spray regime registered lowest disease pressure. Use of multiple fungicide ingredients (Mancozeb (Dithiocarbamate 800g/kg), Consento (Fenamidone 6.7% w/w + Propamacarb hydrochroride 93.6% w/w); Infinito (Propamacarb (55.3% w/w + Fluopicollide (5.53% w/w) and Agrolaxzyl (Metalaxyl 80 g/kg + Mancozeb 640 g/kg WP) at different intervals has demonstrated the potential to suppress the disease to levels not causing serious economic damages by not allowing significant disease development on the leaves, hence has been recommended to be used for the management of late blight in Uganda.