Thanks for the follow-up information, Brian. Using six strep sprays during bloom, while I can see how it may be necessary, does make me a bit more uneasy about selecting for strep resistance. In northeastern United States, we often need two sprays during bloom, sometimes three, and very rarely four. I’ve not been concerned about using four sprays if needed. However, I doubt that anyone has enough experience with the impact of 6 early-season sprays to be certain of the outcome.
One theory about how strep resistance develops (and I think this is still valid) is that the initial selection for resistance is not in Erwinia, but rather in other bacteria that exist in the orchard environment. These other bacterial species may then pass on the strep-resistance genes to Erwinia because bacteria have mechanisms for transferring useful DNA (i.e., DNA that enhances survival) from one species to another. When strep is applied to apple and pear flowers in springtime, the over-all bacterial populations on leaves and in soil are still rather low because bacterial population build slowly as plants and soil warm up. Therefore, there is less selection pressure for resistance in the non-Erwinia species when strep is applied during bloom as compared to after bloom. Bacterial populations in the orchard environment increase very rapidly as temperatures rise, so summer applications of strep impact a much larger universe of bacteria and therefore are presumed to be more likely to trigger resistance that can later be transferred to Erwinia. Strep is broken down in sunlight, but each application may contribute to residual accumulations in the ground cover, duff, or soil surface where the accumulation from multiple applications might persist long enough to enhance selection for resistance in soil bacteria as soil temperatures rise. I really don’t know how long strep persists in orchard soils, and there is undoubtedly huge variations depending on rainfall, orchard cover, soil type, etc. I’m sending this post simply to indicate that there is still a lot of things we don’t know about how our agrichemical products impact the total orchard environment. Given that uncertainty, I’m still willing to bet, based on our history in the Northeast, that limiting strep applications to blossom time in areas that average only two or three strep sprays per year will never result in selection for strep resistance even if growers occasionally use one additional application after bloom to suppress trauma blight following hail or wind storms. However, if you will need more than four strep sprays on a regular basis, that makes me a bit less comfortable and you may want to break up that string of strep sprays by including Kasumin in your blossom spray strategies. On Mar 21, 2015, at 10:09 PM, Brian Heatherington <beechcreekfa...@earthlink.net<mailto:beechcreekfa...@earthlink.net>> wrote: No resistance from bloom sprays is good news. I have had no control problems with copper prior to green tip, strep timed by Maryblyt, Apogee to minimize pruning/harden shoots to possible shoot blight, and control of aphids/leafhoppers at petal fall/1st cover. A few years ago, however, we had a long, extended bloom with Pink Lady. Maryblyt called for a total of 6 sprays (predicted EIP over 100), which exceeds most recommendations of 4 max. I went with the 6 applications and came out OK, but have always wondered if this might trigger resistance. I will stick with strep during bloom and leave the Kasumin for those that need it. I did just put in a block of CrimsonCrisp and haven't thought about putting copper on them. Good advice. Thanks. On 3/21/2015 10:36 AM, David A. Rosenberger wrote: While Kasugamycin works about as well as streptomycin, oxytetracycline is generally a bit less effective and has the disadvantage of preventing bacterial multiplication without killing off all of the bacteria contacted by the spray. Of the three antibiotics, it is my understanding that only strep is absorbed into apple tissue, thereby giving it a bit of an edge over both of the other products, especially in cases where a few infections might have been initiated a few hours before the product is applied. Kasugamycin, like strep, kills bacterial cells that it contacts, but it has the disadvantage of being considerably more expensive than strep. Some of my pathologist colleagues may disagree with me, but I see no reason to pay the extra price for kasugamycin in established orchards that have no history of strep resistance. (An exception would be in countries like Canada where the strep labels allow a maximum of 3 applications/yr.) In eastern New York and New England, we have used strep exclusively for fire blight control for more than 60 years without encountering resistance. Resistance to strep has only appeared in regions where nurseries or fruit growers have used it repeatedly during summer (as many as 12 times/yr) to prevent shoot blight. Thus, there is an abundance of observational evidence that repeated applications of strep after bloom DEFINITELY WILL result in strep-resistant Erwinia amylovora (Ea) whereas, so far as I know, there is absolutely no evidence that multiple applications during bloom have ever resulted in strep resistance. Thus, I would argue that strep is still the cheapest, most effective, and most proven product for controlling blossom blight, and I see no reason to use other products except where strep resistance has been documented or is suspected due to failure of well-timed strep sprays. In fact, alternating with biologicals or with oxytet may actually be counter-productive because they may allow more bacteria to survive, thereby leaving larger populations to be controlled by strep and/or allowing some infections to become established and thus carry the disease through until the next year. Given that there is increasing evidence that fire blight is sometimes present in symptomless nursery trees, one could argue that strep-resistance may show up anywhere as a result of distribution via nursery trees. This is a very real and valid concern. To diminish the likelihood that strep-resistance might be introduced with nursery stock, we in NY have been recommending that all newly planted trees be sprayed with copper shortly after they break bud and then with copper plus strep during bloom. The basis for this recommendation is that copper should knock out strep-resistant Ea on plant surfaces whereas strep will still be more effective for preventing local sources of Ea from infecting flowers on newly planted trees. Using several sprays of Kasugamycin on newly planted trees when they produce flowers during the first year of planting might be even better than copper plus strep for preventing establishment of strep-resistance brought in with nursery stock. Finally, it should be obvious that all new apple plantings should be observed very carefully for evidence of fire blight symptoms for several months after the trees begin to grow, and any diseased trees should be removed immediately. We probably had more fire blight in newly planted trees in 2014 than in any prior year, but it is not a new phenomenon. I ended up with some blight-infested nursery trees in 1986 when I was establishing one of my research orchards. Both in that 1986 situation, rapid removal of diseased trees as they showed up during the year of planting prevented blight introduced in nursery trees from becoming established in my research blocks, and the remaining trees were completely disease-free in subsequent years. However, last year some growers opted to remove all newly planted trees when they found significant percentages of the trees were developing fire blight because it was unclear whether they could successfully identify all of the trees that were carrying the disease. Hopefully there will be less blight in nursery stock in 2015. ******************************************** Dave Rosenberger, Plant Pathologist, Hudson Valley Lab, P.O. Box 727, Highland, NY 12528 Cell: 845-594-3060 http://blogs.cornell.edu/plantpathhvl/blog-2014/ ******************************************** On Mar 21, 2015, at 7:18 AM, maurice tougas <appleman.maur...@gmail.com<mailto:appleman.maur...@gmail.com>> wrote: Would oxytetracycline be an effective economical alternative in those "borderline" instances? Mo Tougas On Fri, Mar 20, 2015 at 10:18 PM, Smith, Timothy J <smit...@wsu.edu<mailto:smit...@wsu.edu>> wrote: HI Brian, Yes, that would work well. Kasumin has worked well in Michigan. Tim From: apple-crop-boun...@virtualorchard.net<mailto:apple-crop-boun...@virtualorchard.net> [mailto:apple-crop-boun...@virtualorchard.net<mailto:apple-crop-boun...@virtualorchard.net>] On Behalf Of Brian Heatherington Sent: Thursday, March 19, 2015 1:29 PM To: Apple-Crop Subject: [apple-crop] Kasugamycin for fireblight Planning ahead for bloom: In an area where fireblight is still effectively controlled by streptomycin, would it be advisable to rotate to kasugamycin for one or more sprays, purely for resistance management? Perhaps when models show a borderline need for application? How effective has Kasumin been in Michigan? -- Brian Heatherington Beech Creek Farms and Orchards 2011 Georgia Highway 120 Tallapoosa, GA 30176 770-714-8381<tel:770-714-8381> _______________________________________________ apple-crop mailing list apple-crop@virtualorchard.net<mailto:apple-crop@virtualorchard.net> http://virtualorchard.net/mailman/listinfo/apple-crop -- Maurice Tougas Tougas Family Farm Northborough,MA 01532 508-450-0844 _______________________________________________ apple-crop mailing list apple-crop@virtualorchard.net<mailto:apple-crop@virtualorchard.net> http://virtualorchard.net/mailman/listinfo/apple-crop _______________________________________________ apple-crop mailing list apple-crop@virtualorchard.net<mailto:apple-crop@virtualorchard.net> http://virtualorchard.net/mailman/listinfo/apple-crop -- Brian Heatherington Beech Creek Farms and Orchards 2011 Georgia Highway 120 Tallapoosa, GA 30176 770-714-8381 _______________________________________________ apple-crop mailing list apple-crop@virtualorchard.net<mailto:apple-crop@virtualorchard.net> http://virtualorchard.net/mailman/listinfo/apple-crop
_______________________________________________ apple-crop mailing list apple-crop@virtualorchard.net http://virtualorchard.net/mailman/listinfo/apple-crop
