白粉病（英文：Powdery mildew）为一种植物常见的真菌性病害，是由不同种类的白粉病源菌所引起，植物受其感染之后，其叶片及枝条上会产生白色粉末状的斑点，因此白粉病是比较容易发现的植物病害之一。白粉病源菌适合生长在在高湿度以及适温下，在植株的地上部任何位置皆可能出现病征，但通常位于低矮处的病征较为明显，随着病情发展，原先的粉末斑点会逐渐扩大而且变密集，并产生大量的无性胞子，使病征蔓延到植株的其他位置。

在农业经营上，有关白粉病的防治与控管相当重要，因为此植物病害会严重影响到作物产量，一般可以透过栽培法的细心控制、喷洒化学农药、提高植物基因耐受力等方法进行白粉病防治。

Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales, with Podosphaera xanthii (a.k.a. Sphaerotheca fuliginea) being the most commonly reported cause. Erysiphe cichoracearum was formerly reported to be the primary causal organism throughout most of the world. Powdery mildew is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of ****ual spores are formed, and the mildew may spread up and down the length of the plant.