Can Mathematical Models Describe Spear Rot Progress in Oil Palm Trees? A Five-Year Black Weevil-Disease Assessment from Ecuador

Oil palm (Elaeis guineensis Jacquin) tree yields may be negatively affected by biotic factors such as Black weevil (Rhynchophorus palmarum L.; Coleoptera: Curculionidae) and Spear rot (Fusarium spp.). This study aimed to identify, model the temporal progress, and correlate Black weevil (BW) and Spear rot (SR) in the highly susceptible varieties INIAP-Tenera and IRHO, under field conditions in Ecuador between 2016 and 2020. Morphological analysis of BW and morphomolecular study of the causal agent of SR allowed us to identify Rhynchophorus palmarum and Fusarium solani, respectively, as biotic factors that affect oil palm trees in Ecuador. The number of adults increased in both genotypes over the years, but much more in INIAP-Tenera (in 2017 and 2019). The logistic model, having a smaller mean square of the residue, was the non-linear model that best explained the SR epidemic in both susceptible genotypes. The incidence of dead palms was higher in INIAP-Tenera trees compared to those of IRHO in the year 2020. Dead plants and the number of insects, and these with the fresh fruit bunches, were correlated significantly. To our knowledge, this is the first report on the positive correlation between dead plants (%) by SR and BW, and the study of both biotic factors in Ecuador.