ABSTRACT
The adoption of a diagrammatic scale that allows for the estimation of the severity of cotton diseases is essential for decision-making in regard to the proper moment to control them chemically. During the main crops of 2000 and 2001 field experiments were carried out, with five replications, using a random complete block design, to compare the reproducibility of estimations of severity of leaf spot caused by Stemphylium spp., Alternaria spp., Ramularia areola and Xanthomonas axopodis pv. malvacearumthrough scores given by 4 evaluators using different diagrammatic scales: one developed by the present authors, one by ANDRADE et al (1999ANDRADE, D.P.F.A.A.; ANDRADE, P.J.M.; STAUDT. R.C. Principais doenças incidentes na cultura do algodoeiro, na região de Chapadão do Sul, MS. CONGRESSO BRASILEIRO DE FITOPATOLOGIA, 32., 1999, Curitiba, PR. Resumos. Curitiba: 1999. p.362-363.), one by CIA et al (1999)CIA, E.; FUZATTO, M.G.; CHIAVEGATO, E.J.; FARIAS, J.C.; ARAUJO, A.E. Desempenho de cultivares e linhagens de algodoeiro diante da incidência de Ramulária In: CONGRESSO BRASILEIRO DO ALGODÃO, 2., 1999, Ribeirão Preto, SP. Resumos. Campina Grande: 1999. p.468-470. and one by CIA & SALGADO (1997)CIA, E.; SALGADO, C. L. Doenças do algodoeiro (Gossypium spp.). In: __________ (Ed.).. Manual de fitopatologia. São Paulo: CERES, 1997. p.33-48. on DeltaOpal cultivar. The evaluations were performed by 4 different appraisers at 66, 81, 100 and 114 days after emergence in the crop year 2000/2001 and at 71, 86, 106 and 124 days after emergence in the season 2001/2002 in 40 marked plants per plot. The diagrammatic scale allowed the evaluators to estimate the severities of leaf spot with different levels of symptoms, in the same plant, showing more uniformity in the results when the severity of the diseases was lower. The CIA; SALGADO (1997)CIA, E.; SALGADO, C. L. Doenças do algodoeiro (Gossypium spp.). In: __________ (Ed.).. Manual de fitopatologia. São Paulo: CERES, 1997. p.33-48. scale demanded more competence from the evaluators for the right use of it for determination of spot severities of the Stemphylium/ Alternaria complex. Scale 1 (created by the authors) and the CIA et al. (1999)CIA, E.; FUZATTO, M.G.; CHIAVEGATO, E.J.; FARIAS, J.C.; ARAUJO, A.E. Desempenho de cultivares e linhagens de algodoeiro diante da incidência de Ramulária In: CONGRESSO BRASILEIRO DO ALGODÃO, 2., 1999, Ribeirão Preto, SP. Resumos. Campina Grande: 1999. p.468-470. scale were more appropriate for the detection of initial symptoms of the ramularia leaf spot.
KEY WORDS
Areolate mildew; stemphylium/alternaria; bacterial blight of cotton; diagrammatic scale for comparison