Research: Research:
A model to predict incidence of papaya ringspot was developed and validated from 5 yr of field observations in central Veracruz, Mexico. The model was developed from 1 yr of data collected from papaya ( PW + 0.116 AG – 0.0058 _{5}AN – 0.0057 _{5}^{2}MP in which _{5}^{2}, y was the incremental increase of disease ( y ) at any given time (_{t} – y _{t–1}t); AN and _{5}, AG_{5},MP were the numbers of the alate aphid species _{5}^{2}A. nerii, A. gossypii, and Myzus persicae, respectively. PW was an interaction variable defined as the product of precipitation (P) and speed and duration of wind from the north (W). Values for independent variables were accumulated during a 4-wk period that ended 3 wk before the calculated incremental increase of disease. The equation accounted for 78% (R^{2} ? 0.78) of the total variation of the change of disease incidence ( y ) in the original data set. Validity of this model was tested with data obtained from 60 epidemics in papaya plantations established from 1987 to 1989 to represent different dates, plant densities, and plantation sites. The model predicted the relative rate of disease increase in 38% of the epidemics (23 of 60, _{t} – y _{t-1}R^{2} ? 0.60). Three other models that accounted for less variance explained in the original data set than the first model (R^{2} < 0.78) were also validated. One model predicted the incremental increase in disease incidence of 40% of the papaya ringspot epidemics (24 of 60) with R^{2} ? 0.60. In this model, the disease incidence change was explained by the independent variables AN and _{5}, AG_{5},PW. |