Further studies on the yield losses of corn leaf blight caused by Helminthosporium maydis Nishikado and Miyake (China)
1987
Zhou, R.H.
A moderately susceptible variety of Luo Yang White dent corn was used as the experimental material and different levels of disease-severity were established by spraying dyrene fungicide at different intervals from 5-20 days. The data obtained were studied by covariant analysis. The relationship betwen corn yield and leaf blight severity were expressed by the following two multiple regression equations: (1) Y = 27.82-0.1368X1-0.1435X2; (2) Y = 23.48-0.1368X1-0.1435X2 where: Y = predicted yield expressed as cattles per plot, each plot equal to 0.032 Mu. X1 = severity of disease at early milk stage (30th Aug) expressed as disease index in percent. X2 = severity of disease at late milk stage (15 Sep). The equation of yield loss, L % = (1 = Y/a) 100, was suggested for use in disease loss assessment, where "a" is the constant of the equation. With respect to the above two equations for predicting yield, equation (1) should be used when the total amount of rainfall during the corn growing season (mid-June to mid-September) is relatively low (3-6 days). Equation (2) should be used when the total amount of rainfall during the growing season is lower (about 160 mm) and the number of rainy days during the early to late milk stage is higher (15 days). It is believed that the equation for predicting yield loss together with the models for forecasting epidemics of the disease can be beneficial in making disease control management decisions such as fungicide application and various cultivation practices.
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