Re: Apple-Crop: herbicide strategyThanks for your response Dave, I had become convinced that something had changed in the commercial formulations of glyphosate. I saw too many trunk canker in orchards where glyphosate alone was used as a stand alone weed treatment. Are you using roundup? had become one of the first questions I would ask when growers called about trunk cankers. ----------------------------------------- Mark Longstroth SW Michigan District Fruit Educator Van Buren County MSU Extension 801 Hazen Street, Suite A Paw Paw, MI 49079 Bus (269) 657-7745 Fax (269) 657-6678 Email - [EMAIL PROTECTED] Check Out My Webpages http://web1.msue.msu.edu/vanburen/disthort.htm -----------------------------------------
-----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] Behalf Of Dave Rosenberger Sent: Thursday, March 15, 2007 2:02 PM To: [email protected] Cc: Mike Fargione; Deborah Breth; Kevin Iungerman; Kerik Cox; Juliet E. Carroll Subject: Re: Apple-Crop: herbicide strategy Here is a long response to Rick Holmgren's question relating to contact herbicides that might cause basal trunk cankers on apple trees. Concerns about contact herbicides causing basal cankers on apple trees emerged in eastern New York beginning in 2001. We continued to accumulate circumstantial evidence over the next five years that implicated glyphosate as part of the problem. Mike Fargione and I published an article (cited and linked below) outlining some of our observations. Rosenberger, D. A. and Fargione, M. J. 2004. Apple tree deaths attributable to herbicides? Scaffolds Fruit Journal 13(13): 3-5. http://www.nysaes.cornell.edu/ent/scafolds/2004/040615.html#diseases. Since that article was published in 2004, I have seen significant acreages of Macoun apple trees destroyed as these basal trunk cankers completely girdled some trees and damaged other trees so severely that they were not longer productive. Other cultivars throughout New York State also showed superficial bark damage that fit the same patterns, but most cultivars were not so severely affected as Macoun. Recently, I've become aware of additional information that may help to further explain our observations. One agrichemical company rep told me that from 2001 through 2005, many manufacturers/formulators of glyphosate modified their original formulations by adding di-ammonium phosphate (or di-ammonium phosphite?) so that these new formulations would work without the addition of surfactant/penetrants that were recommended on the labels of the earlier glyphosate formulations. Apparently the latest glyphosate formulations that were released starting in 2005 moved away from using the di-ammonium salt as an activator. Over the past three months, I have been actively pursuing information on disease control capabilities of the new phosphite fungicides which are absorbed through tree bark and become fully systemic within trees when applied to tree trunks. (This treatment process was developed in California to treat trees for prevention of sudden oak death cause by Phytophthora.) One representative of a phophite manufacturing company told me that these products are highly systemic and will enhance uptake of any other products that are applied with them. This rep said that his company had tested various formulations of phosphites as activators for glyphosate. He said that the phosphites being sold as fungicides are mostly composed of mono-and dipotassium salts of phosphorous acid because the ammonium salts of phosphorous acids sometimes caused phytotoxicity, at least in part because of the ammonium salt's effectiveness as a desiccant. I'm still not certain that I have the correct information on all of the details related to changes in glyphosate formulations. However, it seems possible that the trunk injury that we have observed on Macoun and other trees over the past five years may be attributable to the ammonium salts that were included in glyphosate formulations produced between 2001 and 2005. That would make sense, because I've gone back through my notes for the past 8 years and found no mention of herbicide-related trunk cankers prior to 2001 despite the fact that glyphosate was being used in NY apple orchards for many years before that. Furthermore, if the ammonium salts in those glyphosate formulations contributed to desiccation of the sprayed sections of apple trunks, that desiccation factor would fit perfectly with my earlier hypothesis that something about the glyphosate injury was enabling invasion by Botryosphaeria dothidea, a pathogen known to attack drought-stressed woody plants. The bottom line is that we probably will never be able to prove a glyphosate/trunk canker association because no one has the time, funding, or impetus to do the required research. However, IF the ammonium salts in glyphosate were part of the problem, and IF those salts have now been removed from newer glyphosate formulations, then the problem with basal trunk cankers should gradually disappear. Trees damaged (presumptively) by glyphosate sprays between 2001 and 2005 may take some time to recover, but I would hope that we will not see new cases appearing in previously unaffected orchards. Greetings, I was wondering about what everyone was planning to do about an herbicide program in the coming year. We are trying to move away from post-emergence materials due to the possibility that they are leading to basal cankers in our orchard. Last year, we switched from a glyphosate/gramoxone program to a surflan+oryzalin application really early with a gramoxone touch-up in mid summer. It worked okay, but we had some poison ivy and bittersweet seedlings show up around september. Any thoughts or other ideas? Russell Holmberg Holmberg Orchards Gales Ferry CT -- ************************************************************** Dave Rosenberger Professor of Plant Pathology Office: 845-691-7231 Cornell University's Hudson Valley Lab Fax: 845-691-2719 P.O. Box 727, Highland, NY 12528 Cell: 845-594-3060 http://www.nysaes.cornell.edu/pp/faculty/rosenberger/
