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Poster: Biology & Disease Mgmt: Chemical Control


Sensitivity of Podosphaera xanthii isolates from Illinois to fungicides
Y. XIANG (1), M. Babadoost (2) (1) University of Illinois, Urbana-Champaign, U.S.A.; (2) Department of Crop Sciences, University of Illinois, U.S.A.

Powdery mildew causes more than 50% yield losses in pumpkin and squash fields in Illinois, if it is not managed effectively. Since 2010, growers in Illinois have complained about failure of some fungicides to effectively control powdery mildew in cucurbit fields. This research was conducted to evaluate sensitivity of powdery mildew fungi from Illinois to major powdery mildew fungicide groups, including demethylation inhibitors (DMI), strobilurins or quinone outside inhibitor (QoI), succinate dehydrogenase inhibiting (SDHI), and cyflufenamid. In 2014 and 2015, 34 isolates of powdery mildew fungi were collected from cucurbits fields in 10 counties in Illinois. All of the collected isolates were identified as Podosphaera xanthii by using universal fungi primers ITS1F and ITS4 to amplify the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (nrDNA). Twenty of the isolates from different locations and different hosts were tested for their sensitivity to the four fungicides, including triflumizole (DMI), azoxystrobin (QoI), penthiopyrad (SDHI), and cyflufenamid. Our preliminary studies in the laboratory showed that the isolates were highly sensitive to triflumizole, penthiopyrad, and cyflufenamid, but less sensitive to azoxystrobin. The sensitivity of the isolates to azoxystrobin varied. Similarly, severity of powdery mildew in the field plots treated with azoxystrobin was significantly higher than those in the plots received the other three fungicides.