https://phys.org/news/2018-07-fertilizer-microbiome-ability-disease.html

While the researchers don't yet know whether the increased number of bad bacteria on the leaves actually makes the tomatoes sick, the study clearly shows that fertilizer throws the community of microbes on the leaves off-balance. That potentially could allow disease-causing organisms to enter the plant.

"When we change the nutrient environment that plants are in, we are fundamentally altering the plant-microbiome interaction and also, importantly, the microbiome-mediated protection of natural plant/microbe interactions," said senior author Britt Koskella, a UC Berkeley assistant professor of integrative biology.