Scientists have developed new tools to study a fungus called Diplodia sapinea that damages pine trees around the world. They created a method to genetically modify this fungus and tag its cell nuclei with a red fluorescent marker so they can track the infection process. They also developed a simple way to test infections using young pine seedlings in the laboratory instead of large greenhouse setups. Using these new tools together, researchers can now watch in real-time how the fungus grows inside infected pine plants, which will help develop better ways to protect forests.