Effect of soybean rust and downy mildew on yield loss under natural conditions of Chiangmai: Yield loss estimation
2001
Sunthorn Buranaviriyakul | Sombat Srichuwong
Three soybean cultivars were studied over three years under natural disease inoculation with different fungicide treatments for controlling rust (Phakospora pachyrhizi) and downy mildew (Peronospora manshurica). Yield losses in untreated plots due to rust alone for the most susceptible cultivar (7608) declined from 60.6 percent in 1996 to 0 percent in 1998 for October sowing date but showed an increase from 3.3 to 36.7 percent for November planting date; a similar trend also occurred with the other two cultivars. Effect of downy mildew on yield loss was low. A logistic function was fitted to each set of disease data; the area under the disease curve and disease infection level were obtained and used as independent variables in regression analyses. Single point and area-under-curve models for one and two-disease effects were compared to estimate yield loss. The area-based model was more accurate than the single-point one for both one and two-disease cases. The two-disease model had a higher standard error for the regression coefficient. For practical purpose, the single point model would have a greater utility for crop loss assessment in the field.
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