Researchers studied the fungi living inside grapevine water-conducting tissues in Mallorca, Spain, where a bacterial disease called Pierce’s disease is spreading. They found both helpful and harmful fungi living alongside the disease-causing bacteria. When they tested what happens when both the bacteria and a fungal pathogen infect grapevines together in controlled conditions, the plants became much more severely damaged than with either pathogen alone, suggesting these microorganisms work together to harm the plant.