With ample rain, warm temperatures and high humidity, hop growers should be diligent in applying protectant fungicide applications against downy mildew.
Posted on June 19, 2014 by Erin Lizotte, Michigan State University Extension
Weather conditions across Michigan have been conducive to downy mildew development in hops. Downy mildew infections in northern hopyards have already begun the secondary reproductive cycle which produces the spores that spread this difficult disease. The causal agent of downy mildew, Pseudoperonospora humuli, overwinters in dormant buds or crowns, moving into buds during early spring, and then into the tissue of the basal spikes as shoots expands. The pathogen produces copious spores on the underside of infected leaves. Infection is favored by mild to warm temperatures of 60 to 70 degrees Fahrenheit when free moisture is present for at least 1.5 hours, although leaf infection can occur at temperatures as low as 41 F when wetness persists for 24 hours or longer.
Front and back of relatively new downy mildew infection on hops, taken June 18, 2014. Photo credit: Erin Lizotte, MSU Extension
Front and back of a hop leaf with an advanced and sporulating downy mildew infection. Note the gray, tufted spore masses on the underside of the leaf, taken June 18, 2014. Photo credit: Erin Lizotte, MSU Extension
Copper, boscalid, pyraclostrobin, cymoxanil, fosetyl-Al, metalaxyl, phosphorous acids, dimethomorph, mandipropamid, mefenoxam and a number of biopesticides have varying activity against downy mildew. Cymoxanil, dimethomorph and mefenoxam have performed best in the Pacific Northwest, but have not been evaluated in Michigan.
For more information on management strategies for downy mildew, please refer to the Michigan State University Extension article, “Downy mildew of hops already reported in Michigan.” For a list of products containing these active ingredients, refer to the “Pesticides registered for use on hops in Michigan, 2014” resource.
This article was published by Michigan State University Extension. For more information, visit http://www.cnchemicals.com/. To contact an expert in your area, visit http://www.cnchemicals.com/, or call 888-MSUE4MI (888-678-3464).
Related Articles
-
May 15, 2014 | Erin Lizotte | As the first hop bines emerge, growers are already reporting symptoms of downy mildew infection. Early and consistent protectant spray strategies will be critical to season-long control of this difficult disease.
-
April 25, 2014 | Diane Brown | Review pesticide labels for changes to ensure legal use of pesticides on Michigan-grown hops.
-
January 22, 2014 | Marilyn Thelen | Looking for ways to save money on pest management? Review the integrated pest management (IPM) program on your farm to see that it is being utilized to the fullest.
-
January 17, 2014 | Stan Moore | Emerging important issues will prompt valuable discussion at the 2014 Growing Michigan Agriculture Conference during Agriculture and Natural Resources (ANR) Week.
-
November 14, 2013 | Erin Lizotte | Looking to brush up on your pest management skills? Register now to ensure your spot at this pioneering workshop designed to serve specialty crop, field crop and landscape professionals.