A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>

[1] Delaware and Maryland: alert
[2] Michigan

******
[1] Delaware and Maryland: alert
Date: Wed 9 Jul 2008
Source: University of Delaware, Kent County Agricultural Extension [edited] <http://kentagextension.blogspot.com/2008/07/downy-mildew.html>

Alert -- downy mildew found in cucumbers

Downy mildew has been found in Delaware and Maryland on cucumbers.
Pickle and other cucumber growers need to start fungicide programs at this time.

Downy mildew was observed on cucumber in our sentinel plots this morning (9 Jul 2008) near Georgetown. This indicates that we had a transport event of spores from the south over the weekend as predicted by the NC State Plant Disease Forecast Center. We are recommending that cucumbers be sprayed at this time to protect plants that are at a vulnerable stage of development.

For other cucurbit crops we are suggesting that you wait until the disease is seen on crops other than cucumbers. Be sure to be checking your fields daily especially in areas that had heavy rainfall Sunday
[6 Jul 2008].

[Byline: by Gordon Johnson]

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

******
[2] Michigan
Date: Mon 7 Jul 2008
Source: Michigan Farmer [edited]
<http://michiganfarmer.com/index.aspx?ascxid=fpStory&fpsid=34673&fpstid=2>

Downy mildew confirmed on cucumbers

Downy mildew, a highly contagious fungal disease of cucumbers and other vine crops, has been confirmed in a cucumber field in Monroe County.

Mary Hausbeck, Michigan State University (MSU) professor of plant pathology, confirmed the finding on 2 Jul [2008]. Though the current infection is very light and no fungicides have been applied, Hausbeck recommends that all Michigan cucumber growers should begin spraying for downy mildew immediately and increase their existing field monitoring efforts. "Cucumber growers are at immediate risk," she warns. Hausbeck's research team has downy mildew traps in 3 locations on the east side of the state and 2 in western Michigan. She says spores have been detected in all 5 traps.

Storm events that produced substantial rain and high winds in areas can aid in the diseases spread, she adds. "Downy mildew is not a disease where you can afford to sit and see what happens," she says.
"It spreads faster than other diseases that affect cucumbers, and once you have it, it is very difficult to get under control."

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[Downy mildew caused by the fungus _Pseudoperonospora cubensis_ is a devastating disease of cucurbits and has been reported from different locations worldwide. Different pathovars with variable host preferences seem to exist, and, for example, a strain that affects cucumbers may not necessarily affect melons. By affecting the leaves and thus the photosynthetic potential of its host, downy mildew reduces yield and fruit quality, and it can eventually kill the host plant. If appropriate conditions are present, plantings can be infected so rapidly that they appear to have been frosted.

The fungus survives on cultivated or wild cucurbits, and volunteer cucurbit crop plants or weeds may serve as sources of inoculum. The disease is spread by wind, rain splash, and mechanical means. Control strategies include the use of resistant cultivars as well as fungicide applications.

Spore traps are used for determining identity and time of dispersal of fungi. Spores found in traps are identified by morphology to genus and sometimes species and can indicate the presence of a fungal pathogen before disease is discovered in the field because symptoms need time to develop and may initially be difficult to detect. For more information on spore trapping see links below.

Maps
USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html> and
<http://healthmap.org/promed?v=40,-97.6,4>
US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>

Pictures
Photo gallery of downy mildew on cucurbit species:
<http://www.ces.ncsu.edu/depts/pp/cucurbit/images.php>
Downy mildew on rockmelon upper and lower leaf surfaces:
<http://hgic.clemson.edu/factsheets/graphics/2206/downyupper700.jpg> and
<http://hgic.clemson.edu/factsheets/graphics/2206/downylower700.jpg>
Downy mildew on cucumber leaf:
<http://www.ag.ohio-state.edu/~vegnet/news/currentvn10-06_files/image002.jpg>

Links
Additional news story:
<http://www.monroenews.com/apps/pbcs.dll/article?AID=/20080705/NEWS01/682977669/-1/NEWS>
Cucurbit downy mildew, disease information:
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_Foliar.htm>,
<http://web.aces.uiuc.edu/vista/pdf_pubs/927.pdf>  and
<http://www.avrdc.org/LC/cucurbits/downy.html>
Cucurbit downy mildew pathotypes:
<http://www.ces.ncsu.edu/depts/pp/cucurbit/thedisease.php>
Downy mildew websites of MSU:
<http://plantpathology.msu.edu/labs/hausbeck/ForGrowers.html>  and
<http://www.ipm.msu.edu/downymildew.htm#17>
_P. cubensis_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=120276>
Downy mildew forecast from University of Delaware:
<http://www.ces.ncsu.edu/depts/pp/cucurbit/>
Information on spore traps:
<http://www.weld.co.za/PDF/Flyer_VST.pdf>  and
<https://www.emlab.com/media/reports/STstandard.pdf>.  - Mod.DHA]