Tropical Plant Pathology (2009) 34, 250-255

Renata M. Mesquini, Kátia R.F. Schwan-Estrada, Cláudia V. Godoy, Rafael A. Vieira, Nestor A.H. Zarate and Maria do Carmo Vieira (2009)
Escala diagramática para a quantificação de Septoria apiicola e Cercospora arracacina em mandioquinha-salsa
[Diagrammatic scale for assessment of Septoria apiicola and Cercospora arracacina in Arracacha]
Tropical Plant Pathology 34 (4), 250-255
Abstract: Leaf spots, caused by the fungi Septoria apiicola and Cercospora arracacina, are among the most serious leaf diseases that affect arracacha. Since standardized methods for disease evaluation are necessary, this work proposes a diagrammatic scale for assessment of these diseases. Leaves presenting different severity levels were collected and the minimum and maximum severity limits were determined. The intermediary severity levels were determined according to "Weber-Fechner´s stimulus response law" and the scale had seven severity levels (0.7; 2; 4; 8; 17; 32 and 53%). Scale validation was carried out by four experienced raters and four inexperienced raters, who estimated severity with and without the use of the scale, using 50 leaves with different levels of disease. The actual severity and the estimated severity values were analyzed through linear regression, and the estimates were compared for accuracy and precision. By using the scale, the raters obtained higher precision and accuracy levels, and the variance of the absolute errors in the assessment of the disease presented values within acceptable limits. The proposed scale was thus considered appropriate for evaluation of leaf spots in arracacha.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
(original language: Portuguese)
Full text of article
Database assignments for author(s): Cláudia V. Godoy

Research topic(s) for pests/diseases/weeds:
surveys/sampling/distribution

---

Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Septoria apiicola	Arracacia xanthorrhiza
	Cercospora arracacina	Arracacia xanthorrhiza