LAUSR

Coffee leaf rust caused by Hemileia vastatrix and American leaf spot caused by Mycena citricolor are important fungal diseases of coffee that cause severe yield losses. While coffee leaf rust received much attention based on the recent outbreak in Latin America, we report here on an association pattern of American leaf spot with the presence of coffee leaf rust in a coffee farm in southern Mexico. From 7 months of sampling on 640 coffee bushes in 128 50 × 50‐m plots, we show that the occurrence and severity levels of coffee leaf rust and American leaf spot are not independent. Chi‐squared tests of coffee leaf rust and American leaf spot presence show significantly fewer coffee plants infected with both diseases and more plants infected with only one disease than at random. The resulting patterns of infection are consistent with the hypothesis that there may be trade‐offs in controlling these pathogens, where the leaf rust‐resistant Coffea arabica varieties planted in response to the recent outbreak may be more susceptible to American leaf spot disease. These results underscore the importance of further research on the communities of coffee pathogens and suggest that management strategies for coffee rust control should not rely solely on planting homogeneous resistant varieties.