Powdery mildew is a common disease of cucurbits under field and greenhouse conditions in most areas of the United States. Although all cucurbits are susceptible, symptoms are less common on cucumber and melon because many commercial cultivars have resistance. This disease can be a major production problem if not manage timely.
Podosphaera xanthii and Erysiphe cichoracearum are the two important fungal organisms that cause cucurbit powdery mildew. P. xanthii is a more aggressive pathogen than E. cichoracearum. E. cichoracearum requires a lower temperature optimum and hence, this fungus is found mainly during cooler spring and early summer periods. In contrast, P. xanthii are more common during the warmer months.
The causal fungi are obligate parasites and therefore cannot survive in the absence of living host plants. Possible local sources of initial inoculum include conidia from greenhouse-grown cucurbits, and alternate hosts. Verbena, a common ornamental plant and also a common weed, could be an important source of inoculum.
Pathogenically distinct races of Podosphaera xanthii have been differentiated on muskmelon. Races 1 and 2 have most common in the eastern United States recently.
Fungicides: Quintec, Proline, Torino (rotation in watermelon and cantaloupe)
Proline, Torino, Procure (rotation in other cucurbits)