New downy mildew fungicide available to Michigan hop growers

The Michigan Department of Agriculture and Rural Development has approved the use of Presidio by Michigan hop farmers.

Editor’s note: This article was updated July 13, 2015 to include pre-harvest interval information.

The Michigan Department of Agriculture and Rural Development (MDARD) has approved the use of the fungicide Presidio in Michigan hopyards due to unprecedented downy mildew infection resulting from the extremely wet weather. Presidio cannot be used on hops intended for the export market. The severity of downy mildew this season was caused by high disease pressure from previous downy mildew outbreaks, environmental conditions favorable for downy mildew, fungicide wash-off from frequent rain showers and cultivar susceptibility. At this time there is no special label needed for hop producers to legally apply Presidio; growers can refer to the existing Presidio label for general application guidelines. Eventually, a Section 18 label will be developed with specific directives for hop and will be made available on the MDARD website and required on farm. Michigan State University Extension will provide notice when the Section 18 label becomes available.

Growers may make up to three applications of Presidio 4SC at a 4 ounce per acre rate. The pre-harvest interval (PHI) on hop is 24 days. Presidio should be tank-mixed with another downy mildew product (e.g., Forum, Curzate, Revus or Ranman) and applied at 10-14 day intervals, not in consecutive applications. The current weather pattern across much of the state remains favorable for downy mildew development, so limiting disease will be a challenge.

Wet and humid conditions last fall and this spring have provided ideal conditions for downy mildew to become a problem in even well-managed hopyards. All hopyards, even new yards not exhibiting signs or symptoms of downy mildew, should be utilizing a season-long – from 6-inch bines through harvest – protectant fungicide program to minimize downy mildew infection. Michigan receives a substantial amount of rainfall and days with high humidity which increase the potential for downy mildew infections and makes complete control likely impossible. Even when growers follow best management practices, downy mildew can be a problem. Growers who were able to apply fungicide treatments on a protectant basis ahead of recent rain events are seeing lower infection levels, but still experiencing significant pressure for this time of the season.

For more information about downy mildew management, refer to “Management options for hopyards with downy mildew” from Michigan State University Extension.

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