Glen:
I am glad to see your attention to the details of orchard pest control.
It is not only
you who sometimes feels inadequate when planning just what can be done
to save time
and money while maintaining minimal pest damage.
For you, I guess Flyspeck is the worse of the Flyspeck/Sooty Blotch
category of summer
disease. For me, the worse has always been Sooty Blotch. Since I began
using the combination
of phosphorous acid with captan some years ago, as discussed in one of
Dave Rosenberger’s
Scaffolds articles (June 22, 2009) ,the problem has been infrequent.
This success has
probably been aided also by knowing now that some number of hours (270)
wet fruit is a factor
in when disease can appear if fungicide is not present. I can’t
believe that temperature of
those wet hours is not also involved, but I am not aware that anyone
knows for sure.
Your comments about Lesser Apple Worm reminded me that until I tried
two years of orchard-wide
Apple Maggot trap-out in leu of insecticide, I did not consider LAW to
be an orchard pest. That
was about 25 years ago. Since then I have seen LAW damage only where
insecticide was
not present in the last 3 weeks of August.
David Kollas
Kollas Orchard, Tolland, CT
> On Jun 21, 2017, at 4:12 PM, Glen Koehler <glen.koeh...@maine.edu> wrote:
>
> Seems like a good day to flaunt my ignorance in public
>
> 1) Flyspeck
> Among some of us, what passes for conventional wisdom with regard to
> flyspeck on apple has been that there is a lag period between the end of
> primary scab and the risk of flyspeck infections such that fungicide
> protection in the first few weeks after fruit set is not important.
>
> I'm not sure that's true after reading Ismail, Batzer, Gleason Harrington
> "Phenology of Infection on Apple Fruit by Sooty Blotch and Flyspeck Species
> in Iowa Apple Orchards", Plant Disease
> <https://www.researchgate.net/journal/0191-2917_Plant_Disease>
> 100(2):PDIS-02-15-0137 · December 2015,
>
> Dave Rosenburger showed that maintaining protection in the weeks after
> fruit set made a difference at harvest, which lines up with the Phenology
> paper. Plus Dave said that fungicide stops FS development while the
> fungicide is active, but that after it wears off, FS resume progress towards
> becoming visible. So if you allow a portion of development time, stop it
> with fungistat (vs. -cide), then you have a much shorter lag time between
> last spray and possible emergence of visible flyspeck at harvest. So
> allowing unprotected growth hours in early summer is at the cost of early FS
> progression in the fall.
>
> I am sharing this in hopes of irrefutable brilliance, or at least
> observations from people who have kept up the literature or field trials to
> shed light on this. Bottom line I think the idea that we can wait until 2nd
> generation flyspeck spores are available (if there even is a second
> generation cycle, which for some FS species at least does not seem to be the
> case) before you need to spray idea is a hypothesis not supported by
> evidence.
>
> That all said, uncertainties around development time and residual
> fungicide activity ends up saying that growers should maintain 21-day spray
> interval for continuous protection, which does not conflict with a view that
> FS risk starts early and just takes a long time to show because during mid
> summer it's too hot, and that what really kicks development into gear is
> leaking nutrients as the fruit sweeten and exude sugars in the weeks leading
> up to harvest. This is another idea Dave pitched and which is mentioned in
> the Ismail et al article.
>
> So regardless of the logic, it may not matter if the spray recommendation
> comes out the same. But I'd like to have a less foggy idea about how this
> mob of fungi operate. Make for more interesting thought process instead of a
> blanket 14 (captan alone) or 21 day vs. 2" rain rule (2.5" for Pristine).
> Understanding the mechanics may not make a difference under normal weather,
> but if we get either a long drought or prolonged wet period, understanding
> the target organism could be useful for deciding how to adjust spray
> intervals.
>
> The only evidence I bring to this is a couple of incidents in past years
> when heavy hurricane rains wiped out fungicide coverage in late August, and
> subsequent to that flyspeck showed up right on time with a 270 temperature
> mediated growth hour estimate for when they would appear in trees with FS
> history/pressure. Not exactly Nobel Prize worthy replicated science, but
> kind of made me feel smart for a day or two and that I had some idea what was
> going while flyspeck was busy growing from invisible to visible.
>
>
> 2) Fire blight
> Why is Regulaid specified as a penetrant adjuvant for use with
> streptomycin applications during bloom? Does it have unique characteristics
> that make it better for this purpose than other penetrants such as LI700?
>
> If grower is applying captan at same time, has much strep efficacy is
> lost by not adding the penetrant to the mix to avoid captan phytotoxicity?
>
> Does the marginal leaf discoloration frequently seen after strep
> application have any long term consequences? We saw a lot of that this year
> but I don't think it matters. Does not seem to have affected fruit. If it
> does matter, would spraying during coolest part of the day reduce the
> phytotoxicity risk?
>
> If there is none or even minimal active fire blight in the orchard, is
> there reason to spray strep after hail damage?
>
> Is Regulaid or other penetrant important for tankmix if using strep to
> suppress shoot blight after hail damage?
>
> Does bringing in honeybee hives that were recently in a location with
> high fire blight inoculum create risk of importing fire blight bacteria with
> the bees? I've seen it said that the risk exists, but only last for about 3
> days.
>
> The perennial question of whether you should sterilze blades between
> sanitation cuts to remove fire blight strikes still brings different answers.
> My take on it has been to not bother as long as you are just cutting fire
> blight out, and that it is more important to remove fire blight as soon as
> possible. But to certainly sterilize the blades before using on any other
> trees. Agreed?
>
> Do we all agree that strep provides protection for a flower for about 2-3
> days? But that seems like a moot point because even if strep only acted as
> non-residual sterilizing agent, if a flower is thus protected, by the time it
> could be reinoculated with fire blight bacteria and for those bacteria to
> accumulate enough heat units to generate a threshold population, then that
> flower would be too old to become infected anyway. Though I can imagine
> scenario with temps around 90F where a single cohort of flowers could be
> vulnerable to a second fire blight infection period after receiving a strep
> application.
>
>
> 3) Pheromone trap thresholds
> I stopped using redbanded leafroller traps years ago because I could
> catch dozens or even hundreds per trap per week and not see any damage in
> blocks that received insecticide for apple maggot. If the RBLR trap weren't
> changing any decisions, why bother? I'm almost at that point with lesser
> appleworm. We catch 20-30+ LAW per week per trap, but except in
> organic/low/or no spray orchards, don't see damage. So why bother?
>
> For codling moth, LAW, obliquebanded leafroller, and oriental fruit
> moth, there is a lack of agreed upon threshold. Some sources say 5 moths per
> week per trap indicates a problem, others say 10. And as with LAW, we often
> find well over 10 per week per trap without subsequent damage in blocks
> receiving even rather sparse insecticide protection against apple maggot.
> And the correlation between captures of male moths of these species and
> egglaying females is not strong. The traps are still useful for detecting
> flight timing, but as a quantitative tool are they a reliable indicator?
>
> If useful for indicating threshold abundance of these species to require
> treatment, what threshold value to use?
>
> Thanks for any replies.
>
> - Glen
>
> 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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