The Pathogen Phytophthora infestans belongs to a group of plant pathogens commonly called “water molds” because of their affinity and special adaptations to water. Until the late 20th century, water molds were classified as fungi. However, as their evolutionary relationships were revealed, they were reclassified within the stramenopiles, a group with many aquatic organisms, such as brown algae.
Cucurbit powdery mildew (CPM) has reported on several cucurbit crops in Virginia. This is a little ahead of schedule for this disease to be present, however, this is not surprising considering our mild winter and spring. Symptoms of CPM infection are pretty evident (Figure 1) and starts with initial infection points generally on the upper surface of the leaves. Sparse, white fungal growth can be observed in ‘patches’ on the leaves. As CPM progresses, patches will grow and ‘join’ together to cover the entire upper surface of the leaves (Figure 2). CPM may also be observed on stems and lower leaf surfaces. In general, CPM is most damaging on summer and winter squash, pumpkin, cantaloupe and to a lesser extent on watermelon and cucumber. Infection by CPM earlier in the growing season can lead to premature defoliation and substantial yield loss.
|Cucurbit Disease Update 052212