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

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 of leaf fall. In experimental research, SBR severity is estimated visually aided/trained by a standard area diagram (SAD) developed and validated during the mid‐2000s (Old SAD). In this study, we propose a new SAD set for SBR with six true‐colour diagrams following linear increments (c. 15% increments) amended with four additional diagrams at low (0.95). Low precision (