Aug 8, 2006

Downy Mildew Outbreaks Require Sprays for Control

“All growers of vine crops in Michigan should be spraying for control of downy mildew,” said Mary Hausbeck, vegetable disease specialist at Michigan State University.

“Fungicides will be needed for the duration of the growing season to protect cucurbit crops from downy mildew,” she said. “This disease is extremely destructive and can kill an unprotected crop within seven to 10 days. Since downy mildew is spreading across Michigan, no one should assume that their crop will not become infected.”

Michigan is not alone but does seem in the forefront. Dan Egel, Purdue plant pathologist, said the disease had been identified in only one northern Indiana county, well away from the major melon and pumpkin area to the south. Mohammed Babadoost, plant pathologist in Illinois, said no downy mildew had been found there.

Michigan, by contrast, has seen the disease in 12 counties, two in southwest Michigan near Indiana, two in southeast Michigan near Ohio and five around the Saginaw Bay. Adjacent Ohio and Ontario have also reported downy mildew outbreaks.

There are three elements mandatory for a successful downy mildew control program, Hausbeck said
1. Use only fungicides proven to be effective.
2. Keep the spray interval short.
3. Use ground sprayers.

Data from Michigan State University shows the following program works, she said.
-Spray 1: Previcur Flex (1.2 pt.) + Bravo (or Mancozeb)
-Spray 2: Tanos 50 DF (8 oz.) + Mancozeb (or Bravo)

“All products must be used at full label rates,” she said. “Cutting rates will leave the crop vulnerable to downy mildew.”

Cucurbits grow rapidly and the new growth must be protected, she said.

“That means a five-day spray interval for many growers is the only option.”

Some growers are reporting downy mildew problems in fields that have been sprayed with airplanes, she said. Fungicides for downy mildew control should be applied with ground rigs in a volume of water of at least 30 gallons, with 50 gallons preferred to ensure uniform and thorough plant coverage.

Downy mildew prefers cool conditions, Purdue’s Egel said.

“Finding it here this early is an ill omen. This is the fourth year in a row we’ve found downy mildew in Indiana.”

Spraying for control is expensive, so growers need to correctly assess risk. The penalty is rapid spread of a devastating disease.

Hausbeck concurs. Michigan growers are in for multiple applications from now through the harvest season.

Growers can monitor the national situation at www.ces.ncsu.edu/depts/pp/cucurbit. Michigan information is available at www.plantpathology.msu.edu.