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Pecan Scab Severity-Effects of Assessment Methods.
Clive H Bock1, Bruce W Wood1, Tim R Gottwald2
1United States Department of Agriculture-Agricultural Research Service (USDA-ARS)-Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA 31008.
Plant Disease
|February 7, 2019
Summary
Assessing pecan scab disease severity using the Horsfall-Barratt (H-B) scale showed no accuracy or reliability advantage over nearest percent estimates (NPEs). Rater experience did not consistently improve disease assessment with either method.
Area of Science:
- Plant Pathology
- Agricultural Science
- Mycology
Background:
- Pecan scab, caused by *Fusicladium effusum*, is a major threat to US pecan production.
- Accurate disease assessment is crucial for effective management strategies.
- The Horsfall-Barratt (H-B) scale is a common method for rating disease severity.
Purpose of the Study:
- To compare the accuracy and reliability of the Horsfall-Barratt (H-B) scale against nearest percent estimates (NPEs) for assessing pecan scab severity.
- To evaluate the influence of rater experience on the performance of different disease assessment methods.
Main Methods:
- Pecan scab severity was rated using the H-B scale and NPEs by both experienced and inexperienced raters.
- Lin's concordance correlation coefficient (ρc) was used to assess agreement between methods and raters.
- Bootstrap analysis and regression analysis were employed to evaluate precision, reliability, and time efficiency.
Main Results:
- Agreement with NPEs was variable (ρc = 0.57–0.96), while H-B scale agreement was similar (ρc = 0.59–0.98).
- Experienced raters showed reduced precision and agreement with the H-B scale compared to NPEs.
- Inter-rater reliability with the H-B scale was not superior to NPEs; no consistent time-saving advantage was found for either method.
Conclusions:
- The Horsfall-Barratt scale offers no significant advantage in accuracy, reliability, or time efficiency over nearest percent estimates for assessing pecan scab.
- Rater experience did not consistently favor one assessment method over the other.
- Nearest percent estimates may be a viable alternative for pecan scab severity assessment.
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