Alternative Disease Assessment Method for Cercospora Spot (Pseudocercospora purpurea (Cooke) Deighton) of Avocado (Persea americana Mill.)
Madel van Eeden,
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.
Keywords: Cercospora fruit spot, disease assessment, disease incidence, disease severity, fruit, fuerte, lesion evaluation, preharvest,
South Africa, spore release, temperature, weather.
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