A new standard area diagram set for assessment of severity of soybean rust improves accuracy of estimates and optimizes resource use

• DOI: 10.1111/ppa.13148
• Publication Date: 2020-01-19T07:29:41Z
• Authors: Vinicius T. Franc...; Kaique S. Alves; Sergio M. Mazaro; Cláudia V. Godoy; Henrique S. S. Du...; Emerson M. Del Ponte
• Keywords: Phakopsora pachyrhizi; Soybean rust

Abstract Soybean rust (SBR), caused by Phakopsora pachyrhizi , is the most important yield‐damaging fungal disease of soybean due to severe reduction in healthy leaf area and acceleration fall. In experimental research, SBR severity estimated visually aided/trained a standard diagram (SAD) developed validated during mid‐2000s (Old SAD). this study, we propose new SAD set for with six true‐colour diagrams following linear increments (c. 15% increments) amended four additional at low (<10%) severities, totalling 10 (0.2%, 1%, 3%, 5%, 10%, 25%, 40%, 55%, 70%, 84%). For evaluation, 37 raters were split into two groups. Each assessed 50‐image sample (0.25%–84%), first unaided then using either Old or New SAD. Accuracy, precision, reliability estimates improved significantly relative only when aided (accuracy >0.95). Low precision (<0.78) trend underestimation an increase main issues SAD, which did not differ from estimates. Simulation evaluate impact errors different methods on hypothesis tests, showed that was more powerful detecting smallest difference mean control (e.g., 70% vs. 65% reduction) than SAD; latter required 2‐fold size achieve same power. There need improve some SADs, taking advantage knowledge technology accuracy estimates, optimize both resource use efficiency management decisions.