Extreme maximum temperatures in summer present a significant risk to agroindustry as crops and their ecological interactions have critical thermal limits that can affect their performance and microorganisms-related. Gray mold disease caused by Botrytis cinerea is the most critical disease affecting crops worldwide. In this sense, the impact of temperature on agricultural productivity is well documented in the Northern Hemisphere; the risk of extreme temperatures on the infection rate of B. cinerea in Central Chile is limited. This study analyzes historical climate data from January and February between 1951 and 2023 for the cities of Santiago, Talca, Chillán, and Los Ángeles. The aim was to examine trends in extreme maximum temperatures (EMTs) and develop a simple model to estimate the infection rate of B. cinerea. Linear trend analyses were conducted, as was analysis of the probability of occurrence. Additionally, five-year averages were calculated, and a generic model was presented to assess the effects of warming on the infection rate. The analysis shows positive growth in extreme maximum temperatures in January and February, with projections for 2024, 2025, and 2026 at 70%, 80%, and 80%, respectively. February showed the most significant thermal increase among all stations, with Chillán and Los Ángeles recording higher increases than Santiago and Talca. Projections suggest temperatures near 40–41 °C. The five-year averages for Chillán and Los Ángeles exceeded 37 °C in the 2016–2020 period, the highest values during the analyzed time frame. Trends for 2021–2026 indicate upper limits above 38 °C. These trends, combined with dry summers, could increase the severity of infections and modify the optimal thermal conditions for the pathogen. The results suggest that thermal changes could reduce the infection risk by B. cinerea on fruit crops in Central Chile, and a theoretical approach is proposed to develop predictive tools to facilitate risk assessment in a warming environment.