Characterizing cucurbit powdery mildew in north central Florida

Abstract

Powdery mildew is a common and important foliar disease of cucurbit crops in all major vegetable producing regions of the world. Cucurbit powdery mildew is known to be caused by two obligate pathogens, Podosphaera xanthii (Castagne) U. Braun & Shisshkoff (2000) and Golovinomyces cichoracearum (DC.) V.P. Heluta (1988). In a 2008 study, the disease response on fi ve muskmelon (Cucumis melo L.) differentials planted at two north central Florida locations did not fit the characterization for any one of the physiological races known to be found in the United States. Based on morphological characteristics the predominant pathogen was likely P. xanthii. Fungicide efficacy trials with 16 treatments applied at first sign of disease were established with highly susceptible ‘Butterbush’ butternut squash. Treatments with the fungicides trifl oxystrobin, thiophanate methyl, and trifl umizole resulted in yields that were less than the untreated control in Citra, FL, indicating that there may be some fungicide resistance in the north central Florida powdery mildew pathogen population.