Hi Tim Glad to hear you are still working on E.a. (Congratulation on retirement by the way). I think Maine qualifies as having had infection periods when we are fairly certain that blossom infections occurred. I'm on the road today but will send you Excel data next week. - Glen
On Thu, Aug 13, 2015 at 3:47 PM, Smith, Timothy J <smit...@wsu.edu> wrote: > Hello Everyone, > > > > Re: Fire Blight and models. > > > > I was quite interested in the comment that despite the models indicating > high risk, that you generally did not experience much blight this year. > Also, that it may have been the abnormally dry conditions that may > explain this. > > > > This situation occurs more often than not in the Pacific Northwest. The > infection process modeled by both MaryBlyt and CougarBlight requires (*in > this order*): > > First, Open blossoms, something easy to see, but often overlooked post > primary bloom, when secondary bloom are often present especially on trees > with dwarfing rootstocks. > > > > Second, Contamination of the stigma surface by E. a. bacteria, which is > difficult to detect rapidly, but there is ongoing research on this issue. > “CougarBlight” asks you to adjust your temperature risk thresholds and use > your orchard history and judgment here. This contamination is not present > on most flowers in most orchards, but if there are cankers nearby, this > situation degrades rapidly, and many flowers are contaminated, the closer > to the canker source, the higher the risk. I think there are more sources > of fire blight bacteria in the general environment in the northeastern USA > due to your woodlots and forests (with feral apples and native hosts such > as Hawthorne) as contrasted with the treeless conditions around many > eastern Washington orchards. > > > > Third, Sufficient heat over sufficient time to enable the bacterial colony > to reach the numbers necessary to cause flower infection. There is an > interaction between this factor and the number two factor. Larger initial > colony size will reduce the amount of time and total heat necessary to > colony to reach this hundred thousand to 1 million bacteria colony size > necessary for infection. IT sounds as if these conditions were met very > well in the East this season. > > > > Fourth, the sufficiently contaminated flowers must be lightly wetted to > allow the bacteria to move from the stigma surface into the nectaries. > Then the battle begins. The bacteria need to thrive in the nectary in order > to reach numbers sufficient to switch on their virulence. Once this is > accomplished you have an infection. > > > > In the Pacific Northwest we have plentiful supply of open apple and pear > flowers over an extended period of time. Fire blight is relatively rare in > any given region most seasons, so most growers can assume little pressure > from the bacteria during most seasons. We spent a lot of time emphasizing > sanitation because a little fire blight one year can carry over and lead to > great deal of fire blight the next year. Because of this documented common > lack of contamination of flowers by E. a., we very often experience a > series of days of temperatures sufficient to lead to fire blight, but with > only scattered subsequent fire blight showing up over the next two or three > weeks. We are often able to attribute that scattered blight to dew > formation on flowers, as it often occurs in areas that are more prone to > dew, such as frost pockets or other low areas in the orchard. When we > have a rainy day after a series of warm days, those areas that have been in > bloom during those warm days have increased experience with more common and > severe fire blight, which in this case depends on the presence or absence > of E. amylovora. > > > > CougarBlight was developed where blossom wetting is an exceptional event. > I try to counsel people using this model in areas where blossom wetting is > common to look at the heat risk as primary, and to assume the blossom > wetting will occur, often almost every night. Dew and rain are the rule > rather than the exception in many areas where apples and pears are grown. > This doesn't change the principle of the model that heat is the driver for > infection, the blossom wetting is the trigger for the infection event. > > > > We can learn a great deal about interpreting models by looking at the > weather data around the time that we are fairly certain that isolated > infection events occurred. We can also look at when expected infections > did not occur. It would be very helpful to me if any of you would share > weather data including rainfall, hourly temperature (or daily temps) and > especially leaf wetness readings. Please send data that covers days from > first bloom to about 3 to 4 weeks after petal fall. Excel files are a real > time saver. > > > > Thank you. > > > > Tim Smith > > WSU (Emeritus) > > > > 4. > > > > > > > > *From:* apple-crop-boun...@virtualorchard.net [mailto: > apple-crop-boun...@virtualorchard.net] *On Behalf Of *Daniel Cooley > *Sent:* Wednesday, August 12, 2015 11:22 AM > *To:* Apple-crop discussion list <apple-crop@virtualorchard.net> > *Subject:* Re: [apple-crop] Looking for comments on fire blight management > > > > A group of us wrote the article attached for the UMass/Rutgers publication > Fruit Notes/New Jersey Horticultural News. *MailScanner has detected a > possible fraud attempt from "urldefense.proofpoint.com" claiming to be* > http://umassfruitnotes.com/v80n2/Cover802.html > <https://urldefense.proofpoint.com/v1/url?u=http://umassfruitnotes.com/v80n2/Cover802.html&k=EWEYHnIvm0nsSxnW5y9VIw%3D%3D%0A&r=VR1vaGJPOzxhk9dUVIL5%2Bg%3D%3D%0A&m=UfabeZAWBFZVVH4RygbVAxxf%2BYztNRlyB0BCPGgl9kE%3D%0A&s=6f16d747d2ee23b3be62b4005b0a579f17fdd4826d89fe8c7fc83eb8b4a9b1a6> > The key point is that even in those years when fire blight doesn’t do much, > and particularly the following year, people need to stay alert. Yes, fire > blight can be kept at non-damaging levels, but it takes regular attention > every year. > > > > This year in southern New England and the Hudson Valley, the two fire > bight models, Maryblyt and CougarBlyt, alone or in NEWA, Ag-Radar and other > decision support tools, shot off the charts warning of unprecedented fire > bight risk. Growers in the region had experienced a bad year last year, and > were generally ready to use strep early and often during bloom. Fire blight > never really appeared at problematic levels. > > > > Much to our puzzlement, this was true even for trees that didn’t get strep > treatments, leading us to wonder what was going on with the models and the > disease. The best we have so far is that it was so dry during bloom in most > areas that even though epiphytic populations of bacteria were tremendous, > they never got washed into flowers to cause infection. Another possibility > is that the extremely dry weather suppressed bacterial growth, something > not taken into account in the models. > > > > Dan > > > > _______________________________________________ > apple-crop mailing list > apple-crop@virtualorchard.net > http://virtualorchard.net/mailman/listinfo/apple-crop > > -- Glen Koehler University of Maine Cooperative Extension Pest Management Office Voice: Office 207-581-3882, Cell 207-485-0918 491 College Avenue, Orono, ME 04473
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