Alternative Disease Assessment Method for Cercospora Spot (Pseudocercospora purpurea (Cooke) Deighton) of Avocado (Persea americana Mill.)

The most serious pre-harvest disease of avocado in South Africa is still Avocado Black spot (Cercospora spot). Two methods were compared to assess Cercospora infection. The conventional assessment method (CA) relies on a disease intensity rating system that classifies fruit as local, export or rejects market quality. The disease incidence and severity assessment method (ISA) combines spore release intensity (through a weather based prediction formula) with disease intensity on fruit (as measured for specific lesion sizes representing different infection periods). In the current study, Fuerte avocado fruit from the Limpopo Province in South Africa was subjected to both CA and ISA. Data obtained through CA proved to be very limited and only reflected total disease control at the end of the season. ISA allowed a more detailed assessment of the spray program and it was possible to evaluate the efficiency of individual spray applications. Both the effect of environmental influences on disease severity and the resulted disease intensity can also be evaluated through ISA visualization.