Impact of Diseases on Wheat Yields in Idaho’s Kootenai Valley in 1981. M. V. Wiese, Professor of Plant Science, University of Idaho, Moscow 83843. T. Herrman, Graduate Research Assistant, and M. Grube, Program Analyst, University of Idaho, Moscow 83843. Plant Dis. 68:421-424. Accepted for publication 9 December 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-421.

About 10,000 A (4,050 ha) of winter wheat is grown annually in a disease-prone environment in Idaho’s Kootenai River Valley. In the spring of 1981, fungicide sprays were applied to replicated plots within selected winter wheat fields spaced along the 20-mi. (32.2-km) valley floor. The objective was to selectively control portions of the anticipated disease syndrome, measure any resultant change in disease and yield levels, and quantify the wheat yield loss in the valley attributable to diseases individually and collectively. In 1981, foot rot, powdery mildew, leaf rust, tan spot, sharp eye spot, and stem rust developed in control plots. Preferential control of foot rot and tan spot with benomyl applied in early spring and selective control of leaf rust and powdery mildew (with butrizol and ethirimol, respectively) increased yields from 73 bu/A (4,906 kg/ha) to 84 (5,645), 78 (5,242), and 74 bu/A (4,973 kg/ha), respectively. A repeated benomyl and triadimefon spray treatment controlled foot rot, leaf rust, and tan spot and increased yield to 96 bu/A (6,451 kg/ha). Significant negative correlations between yield and foot rot, leaf rust, tan spot, and sharp eye spot were uncovered. The impact of diseases on yield also was investigated using stepwise multiple linear regression equations that described yield as a function of one or more diseases and disease levels. Total yield loss due to disease was 23 bu/A (1,546 kg/ha) when measured in the field and 38 bu/A (2,554 kg/ha) when estimated from multiple linear regression equations.

Keyword(s): crop loss assessment, disease measurement, disease stress, yield loss assessment.