By SHELLY STRAUTZ-SPRINGBORN
Michigan Correspondent
 
EAST LANSING, Mich. — Downy mildew has been confirmed in cucumber fields in two Michigan counties.

According to Michigan State University Department of Plant Pathology Professor Mary Hausbeck, the disease has been found on farms in Monroe County in the southeastern corner of the state, and in Allegan County in southwestern Michigan. The July 9 finding in Allegan County prompted her to issue a statement to the state’s cucumber growers advising them to “apply downy mildew fungicide immediately.” In a report on her website, Hausbeck wrote, “Finding downy mildew on the west side of the state is very important and likely means that the pathogen is now widespread in the state.”
Her research team has downy mildew traps in three locations on the eastern side of the state and two in western Michigan. She said spores have been detected in all five traps.

“Cucumber growers are at immediate risk,” Hausbeck said. “We need to be scouting fields for other outbreaks of downy mildew, because we really need to know where it is so growers can take appropriate actions.”

Downy mildew causes symptoms on leaves similar to mosaic or angular leaf spot. A distinguishing symptom of downy mildew is dark, purplish-gray fuzz on the underside of the leaf that gives it a “dirty” or “velvety” appearance. The fuzz may be most evident in the morning and can infect leaves of all ages.

The infected fields are being closely monitored, but scientists are concerned about the airborne spread of spores to other areas.
“While the number of spores is low, it tells us our fields have been exposed,” Hausbeck said.

Downy mildew was detected about a month ago in cucumber fields south of the Canadian city of London, Ontario. About 10 percent of the plants were infected by the downy mildew with one to two leaves showing disease. At the time, Hausbeck advised growers to be on the lookout for the disease in Michigan.

After the initial finding on July 2 in Monroe County, Hausbeck said storm events increased the risk of spores being spread.
“Even in those areas of the state that didn’t receive two-plus inches of rain, there was a lot of wind that will cause the organism to spread,” she said.

Spraying strategies are different for fields that have not shown downy mildew than for those where infections are found. Updates on the movement of downy mildew in Michigan, and Hausbeck’s recommendations for spray applications in both cases, may be found at www.plantpathology.msu.edu/labs/hausbeck/ForGrowers.html

“Downy mildew is not a disease where you can afford to sit and see what happens,” Hausbeck said.

“It spreads faster than other diseases that affect cucumbers, and once you have it, it is very difficult to get under control.”
While other vine crops, such as pumpkins and squash, have not been hard-hit by the disease in past years, growers should continue to look for symptoms.

Growers who believe they have downy mildew in their cucumbers, cantaloupes or other vine crops should contact their local extension office immediately to report it.