As well as physical barriers, plants have chemical defences. Many plants make antimicrobial substances. These are chemicals that kill bacteria and fungi or stop them growing. Some are made all the time and others are made only after an infection starts. If a pathogen gets past the cuticle and the cell wall, these chemicals help to stop the infection spreading.
Some plants also make chemicals that are poisonous to animals that eat them, such as insects. People use some plant chemicals as medicines and antiseptics, because the same substances that protect the plant can act against microbes.