Epidemics caused by Mycosphaerella caryigena and its impact on the defoliation of the pecan tree

Abstract

In the pecan tree, the fungus Mycosphaerella caryigena is the causal agent of the pecan downy spot, which causes injury on foliage and defoliation. In the years 1998, 1999 and 2014, ten epidemiological models of lesion/leaf vs time were evaluated. In 1992, epidemiological models were tested for the capture of spores vs. time. In 1998, lesions / leaf defoliation and defoliation vs time was also evaluated. The epidemics of 1998, 1999 and 2014 fitted the models of Logistic Ln, Gompertz and Logistic Ln, respectively. Defoliation of pecan tree by M. caryigena began in August 1998 and ended with 95 % in September. The Gompertz and Log₁₀ models were the best fit for defoliation vs time and lesions/leaf vs defoliation with R²Â 0.924 and 0.937, respectively. The capture of spores of M. caryigena was > 50% from April to May; the monomolecular model was the best fit to the capture of spores (R²Â 0.948). The lesions/leaf appeared in June and were > 100 in September, just when the defoliation reached > 90%. The models lesions/leaf vs time, suggest prolonged periods to produce the inoculum and the incubation of the fungus on the leaf, which coincides with what is known of the disease cycle.