On several occasions this summer the question was posed to me if it was okay to mix the fungicide Serenade with copper. Serenade is a biological fungicide that is OMRI approved and can be used in certified organic production systems. I have used Serenade tank-mixed with copper for many years in my studies (Organic Heirloom Studies) and on my own farm. At an organic tomato workshop this summer, one of the attendees said that Serenade and copper should not be mixed together because the copper would inactivate the Bacillus subtilis in the Serenade, rendering it ineffective. When I returned to my office I did a Google search on the topic and indeed found two university extension articles and several non-professional articles that said the two products should not be mixed because the copper would inactivate the Bacillus subtilis.
Concerned that I might not be giving out the best information, I contacted my resident plant pathologist who passed my question on to the folks at Bayer CropScience. Dr. Dennis Warkentin quickly responded, and with his permission, here is what he said,
Dr. Denise Manker, also of Bayer CropScience, asked me to add that that there is also no loss of foliar activity due to UV/sunlight.
So, those of us who find Serenade plus copper to be effective can continue to use it without concern that we are losing some activity as a result and others might want to try it out next season. Remember that according to the National Organic Program, copper must be used in a manner that minimizes accumulation in the soil.
And thank you to Dr. Warkentin and Dr. Manker for the speedy replies!