Scientists have created a new way to study powdery mildew fungus, which causes widespread plant disease but cannot normally be studied in the laboratory. They identified a related fungus species (Arachnopeziza) that can grow in culture and can be genetically modified. By sequencing the DNA of these two Arachnopeziza species and developing methods to alter their genes, researchers have created a practical tool to understand how powdery mildew becomes dependent on its plant host, potentially leading to better disease control strategies.