.

Date: July 3, 2007

[1] USA (Ohio)
[2] USA (Michigan), Canada (Ontario)

******
[1] USA (Ohio)
Date: Wed 27 Jun 2007
Source: The Beacon Journal [edited]
<http://www.ohio.com/mld/beaconjournal/17425446.htm>

A potentially devastating mildew has been found on cucumber farms in northern Ohio, and Ohio State University vegetable experts are asking growers to take measures now to prevent heavy damage.

The downy mildew was confirmed in a cucumber field in Medina County on 21 Jun [2007] and in Erie County on 25 Jun [2007], reported Sally Miller, a plant pathologist with the Ohio Agricultural Research and Development Center in Wooster and a vegetable-crops specialist with Ohio State University Extension.

The outbreak follows a report of the disease in southwestern Ontario on 8 Jun [2007]. Officials do not know the source of the spores that triggered the Ohio outbreak, but Ohio cucumber growers should be vigilant, Miller said. She is recommending that all cucumber growers in northern Ohio check their fields and protect their crops with one of 4 protectant fungicides. Organic growers in high-risk areas may want to apply a copper-based fungicide to their cucumbers on a weekly basis when weather conditions are favorable for the disease. The weather has been warm and dry with some heavy rains.

The spores are found in the winter in Mexico and southern states. The fungus can be carried north by winds or storms, but Miller said the outbreak could be from greenhouse production in Canada. Last year [2006], the disease hit cucumber farms in Ohio and Michigan and cost growers millions of dollars in lost crops and fungicide costs.

The mildew first appears as pale green areas on the upper leaf surfaces. They change to yellow angular spots. A white to gray downy growth soon appears on the lower leaf surface. Infected leaves generally die but may remain erect while the leaf edges curl inward.

Ohio has nearly 300 cucumber farms that cover about 3100 acres (about 1255 hectares). In 2006, those farms raised 20 900 tons of cucumbers with a value of USD 8.3 million, says the Ohio Department of Agriculture.

(Additional information available at
<http://www.ag.ohio-state.edu/~vegnet>)

[Byline: Bob Downing]

--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator <dodds@ucr.edu>

******
[2] USA (Michigan), Canada (Ontario)
Date: Fri 29 Jun 2007
Source: Detroit Free Press [edited]
<http://www.freep.com/apps/pbcs.dll/article?AID=/20070629/FEATURES04/706290331/1025/FEATURES>


Michigan's 1st 2007 cases of downy mildew, a disease that can wipe out entire fields of susceptible crops, have been confirmed on cucumbers this week [25-30 Jun 2007]. It was found at a home garden and on plants in a commercial grower's fields, both in Monroe County.
Michigan is the nation's leading producer of pickling cucumbers.

Symptoms are yellow or dark spots on the leaves and black spores on the leaves' undersides. Downy mildew invades the leaf tissue, stealing nutrients the plant needs for fruit production.

All commercial cucumber growers in Michigan are being urged to begin fungicide sprays immediately and repeat them every 5 to 7 days. Crops of pumpkins, melons, cantaloupes, squash, zucchini, and gourds, which may also be damaged or destroyed by downy mildew, should be sprayed every 7 to 10 days, according to Mary Hausbeck, plant pathologist at Michigan State University (MSU).

She also asks that home gardeners check their plants for downy mildew and recommends they spray susceptible crops with a copper-based fungicide every 7 days. Gardeners whose plants get downy mildew should pull out the plants and put them in sealed plastic bags to discard them, said Dean Krauskopf of the MSU Extension. Placing the plants in sealed bags should prevent spores from spreading through the air to other gardens as well as to commercial fields.

Nearly simultaneous outbreaks of downy mildew have been reported recently in Ohio and upstate New York. Downy mildew on cucumbers has long been a problem in the south but was not reported in Michigan until 2005. Scientists speculate it arrived with winds following hurricanes or on seedlings that originated in the south. Earlier this month [June 2007], downy mildew was reported on cucumbers being grown in greenhouses in Essex County, Ontario (Canada), across the Detroit River from Michigan.

[Byline: Marty Hair]

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

[Downy mildew on cucurbits is caused by the fungus _Pseudoperonospora cubensis_. However, different strains with variable host preferences (pathovars) seem to exist and it is not uncommon to see squash, rock melon (cantaloupe), and cucumber severely affected while watermelons nearby show no signs of disease. _P. cubensis_ is found worldwide, but it is most damaging in tropical and subtropical areas. By affecting the leaves and thus the photosynthetic potential of its host it reduces yield and fruit quality, and it can eventually kill the host plant. It is an obligate parasite surviving on cultivated or wild cucurbits and is spread by wind, rain, and mechanical means.
Disease development can occur over a wide temperature range under conditions of high humidity. Control strategies include the use of resistant cultivars and fungicide applications.

The related species _P. humuli_ causes a devastating disease of hops.
Downy mildews in other genera cause serious diseases of grapevine, sunflower, and a number of vegetable crops.

Maps
US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>
Canada:
<http://www.supplychainsites.com/images/canada_map.gif>

Pictures
Downy mildew on cucumber leaf:
<http://www.ag.ohio-state.edu/~vegnet/news/currentvn10-06_files/image002.jpg>
Photo gallery of downy mildew on cucurbit species:
<http://www.ces.ncsu.edu/depts/pp/cucurbit/images.php>

Links
Additional news stories on the topic:
<http://www.ohio.com/mld/beaconjournal/news/state/17429811.htm>  and <http://www.cleveland.com/news/plaindealer/index.ssf?/base/medina/118301983981420.xml&coll=2>
Cucurbit downy mildew pathotypes:
<http://www.ces.ncsu.edu/depts/pp/cucurbit/thedisease.php>
Disease information and control strategies:
<http://web.aces.uiuc.edu/vista/pdf_pubs/927.pdf> and <http://www.avrdc.org/LC/cucurbits/downy.html>
Hausbeck Lab website:
<http://plantpathology.msu.edu/labs/hausbeck/Hausbeck%20Lab%20For%20Growers.html>
_P. cubensis_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=120276>.  - Mod.DHA]

[see also in the archive:
2006
----
Downy mildew, cucumber - Canada (ON), USA (MI) 20060803.2149
2003
----
Downy mildew, squash - Italy (Latium, Umbria) 20030401.0803]

The news item on this page is copyright by the organization where it originated - Fair use notice

Other news from this source