Comparing tar spot epidemics in high-risk areas in the United States and Honduras

Tar spot of corn is a disease that causes significant production losses in the Americas. However, the dynamics of tar spot epidemics in different countries is currently unknown. We assessed the temporal dynamics of tar spot epidemics from six efficacy trial experiments conducted in the United States (US) (three) and Honduras (three) from 2019 to 2021. Data collected corresponded to different canopy positions (lower, middle and upper). In all experiments and canopies, treatments contributed to reducing disease as compared to non-treated controls. In the US the time from disease onset (<i>y</i>_<i>ons</i>) to maximum disease level (<i>y</i>_<i>max</i>) was longer than in Honduras. In all experiments, the disease developed from the lower to the upper canopy. The logistic model described well the disease progression data in its linear and non-linear form. Overall, the linear rates (<i>r</i>_<i>L*</i>) were lower in the US than in Honduras, but in the US the highest rates occurred in the upper canopy, while in Honduras they occurred in the lower canopy. Logistic non-linear rates were in general higher in the US than in Honduras. Multi-treatment meta-analysis and the effect size showed that <i>y</i>_<i>ons</i>, <i>r</i>_<i>L*</i>, standardized <i>AUDPC</i> and <i>y</i>_<i>max</i> were higher in Honduras than in the US in the lower canopy and higher in the US than Honduras in the upper canopy. The best correlations occurred in the lower canopy in Honduras or the upper canopy in the US. The information generated in this study helped identify differences in epidemiological dynamics in high-risk areas in two countries.