Cucurbit Downy Mildew and Powdery Mildew Early

There have been unusually early reports of both downy mildew (Pseudoperonspora cubensis) and powdery mildew (Podosphaera xanthii and Erysiphe cichoracearum) on cucurbits in the southeast this season.


Growers are encouraged to be on the lookout for these diseases and to call their local cooperative extension office if they need identification help, management recommendations and to report disease.

DOWNY MILDEW
Southeast Farm Press. May 11. 2012: Downy mildew showing up early in cucumbers.

Cucurbit Downy Mildew Found in NC, Rapid Response and Implications for Local Growers.

Frank J. Louws (1), Wendy Britton (1), Peter Ojiambo (1) and Billy Little (2). (1) Department of Plant Pathology, NCSU; (2) Cooperative Extension, Wilson NC.

There was a confirmed report of cucurbit downy mildew (CDM) in a hoop house in Wilson County, NC on May 3, 2012.  The house contained 2 rows of trellised cucumbers and about 20 vines had early symptoms.  The infection was about 5% and with actively sporulating lesions.

Wilson Cooperative Extension, the NCDA, NCSU specialists, and the CDM ipmPIPE team actively worked to contain this outbreak as soon as possible. Discussions with the grower, industry representatives, and state/University employees reached a quick consensus that the best course of action was to destroy all cucumber vines. The vines were cut, roots extracted, all debris swept up and placed in plastic bags. The contained plant material was carried from the greenhouse and buried at the edge of a field that will not be cultivated this season. This was completed and verified as of 2:00 pm Friday May 4, 2012.

CES and industry knowledge about the area suggested field cucumbers were not present in the vicinity and the inoculum from the hoop house presented a zero to low risk to the industry as a whole. The CDM ipmPIPE subsequently changed the status of this outbreak from "confirmed" to "no longer found".  The county in NC will remain on the map but will not be forecasted as an active source. This data is available at http://cdm.ipmpipe.org.

The only other recorded incidence of CDM is in south Florida. Based on recent weather patterns, there is no evidence the inoculum originated from south Florida and there are no field reports of CDM north of south Florida. A thorough examination suggested the grower used optimum best management practices regarding sanitation, removal of all volunteers and other standard practices. Thus, the source of inoculum remains unknown. However, early detection, rapid destruction and historical weather patterns provide high confidence the problem was contained and does not represent a threat to the industry. At this time, we would not recommend implementation of spray programs to manage CDM in cucumber fields in NC. Monitoring of local fields and forecasting spore dispersal from known sources in south Florida will continue and observations will be posted at the CDM ipmPIPE website.

For further information or questions do not hesitate to call Dr. Frank Louws 919-515-6689 or email frank_louws@ncsu.edu (use subject line Downy Mildew).  

To view previous posts on cucurbit downy mildew click here


POWDERY MILDEW
Dr. Tony Keinath, Clemson University Extension Plant Pathologist, sent out a Timely Talk Update about the presence of powdery mildew on watermelons already this season.  To learn more go to Early Outbreak of Powdery Mildew on Watermelon in South Carolina.

To learn more about cucurbit powdery mildew click here.