Yea, look at me, given my old(er) age -- the NRVART (Newspaper
Readability Venturia Ascospore Release Threshold) depends on: the
light level (civil twilight, nautical twilight, astronomical twilight?
see: , distance reading the
Newspaper (far is probably better I am farsighted, oh not really,
actually I am presbyoptic,
see:, font size (obviously),
and whether or not I can find my eye glasses. (Forgetfullness, sorry,
not in Wikipedia, but my bi-focal glasses are no-line TransitionsTM,
CriizalTM no-glare/reflections, about $250 each at Costco or WalMart
if I buy the cheaper frames.)  Oh, and does the NRVART include reading
the newspaper on an iPad?

But BTW, I can perfectly relate to the PDBA fireblight index!

Sorry to downgrade an otherwise excellent discussion!



On Sun, Apr 24, 2011 at 6:20 PM, Dave Rosenberger <> wrote:
> Hey, Dan --
>        I believe that the "reading a newspaper" threshold for ascospore
> discharge was a verbal comment from either Gadoury or MacHardy.  Given my
> failing memory, I can't be absolutely certain that my recollection is
> correct. Anyway, this may be one of those "rules of thumb" that never make
> it into the scientific literature, probably for the same reasons that my
> personal discomfort model for timing strep sprays for blossom blight will
> never make it into a refereed journal.  After all, we're concerned about
> trying to calibrate leaf wetness meters:  Just think about trying to
> calibrate humans as biological sensors!!
>> David,
>> The original night-time release study was published by MacHardy and
>> Gadoury in 89. It's here:
>> In 98, Gadoury, Stensvand and Seem revised this to take into account some
>> night-time release, saying that in high inoculum orchards night-time release
>> could be a problem. That article is here:
>> I've been looking all over for the source article for Dave Rosenberger's
>> Newspaper Readability Venturia Ascospore Release Threshold, but haven't
>> found it. I did, however, find his Personal Discomfort Blight Alert for
>> blossom blight:
>> "... severe blossom blight infection periods often occur on days when
>> moderate physical activity causes me to break into a noticeably
>> uncomfortable sweat.  The discomfort comes from a combination of high
>> temperature, high humidity, and lack of acclimation to summer temperatures.
>>  If I sense PDBA conditions when trees are in bloom, then I know that a
>> blossom blight spray is needed immediately."
>> Degree days and leaf wetness sensors are interesting and helpful, but
>> sometimes nothing beats the low-tech approach!
>> Dan
>> On Apr 21, 2011, at 11:33 PM, David Doud wrote:
>>>  thank you Dave for the time and effort you put into this post -
>>>  short of input from specmeters, I'll slightly exaggerate and say that
>>> the Cornell model will predict scab infection after a short heavy dew, while
>>> the WA model requires rainforest conditions for a couple of days before it
>>> indicates concern - I made the assumption that if growing McIntosh in NY one
>>> had better be very careful, while desert conditions don't provide the
>>> humidity or inoculum to result in scab infections except under the most
>>> severe circumstances - I talk to growers at the Ohio River and south and
>>> they don't worry much about scab, it's a minor consideration in their
>>> climate -
>>>  the Mills table (and modified Mills - I attended a number of the MI IPM
>>> schools in the '80s when Jones and Howitt and Bird and crew was cutting
>>> edge) has been reliable here and referred to for as long as I have been
>>> spraying apple trees - I used to get up in the middle of the night, check
>>> temperatures, shake limbs to judge free moisture, then refer to the chart to
>>> find out just how much trouble I was in - much, much easier to let the
>>> instrument keep track of conditions - and until this little event, I hadn't
>>> really considered that it would possible to confuse the program - I feel
>>> lucky to have some decades of experience to guide decisions, hence the long
>>> day today putting a protectant cover on in anticipation of the 4 wet days
>>> forecast for the immediate future -
>>  >
>>>  I have heard talk from various sources on the ascospore/light
>>> association, but have never read any source material - can you point me
>>> toward the research that led to this conclusion?
>>>  I find nothing to disagree with and little to add to your observations
>>> about decision factors - thank you -
>>>  David
>>>  the Mills table has been an effective tool here
>>>  On Apr 21, 2011, at 11:13 AM, Dave Rosenberger wrote:
>>>>  Hello, David --
>>>>      I really don't know how the Spectrum  instruments are programmed,
>>>> and I don't know what they are using for the Washington scab model.  Thus,
>>>> this response may be of limited usefulness.
>>  >>      I suspect that that the differences between the Cornell and the
>> Mills (MI) models relate to two key differences among these models.  Again,
>> I don't know this for a fact because I don't know how Spectrum programmed
>> their unit, but I would guess that the Mills (MI) model uses the modified
>> Mills Table that was published by Al Jones and he put into the original
>> Reuter-Stokes scab caster.  If so, that program will not discount wetting
>> periods that start after dark, and it will use slightly longer wetting
>> requirements for light infections than those used by the Cornell model.
>>>>      The Cornell model presumably does not count wetting periods that
>>>> start after dark because relatively few ascospores are released in the
>>>> absence of light.  In a high inoculum block, those few that do discharge at
>>>> night can still create problems, but in most commercial blocks night-time
>>>> discharge will not be significant, especially early in the season.  In my
>>>> opinion, ignoring night time discharge is a bit more risky by the time one
>>>> gets to pink bud (when most ascospores are maturing), and it is absolutely
>>>> foolhardy to ignore night time discharges between pink and petal fall if 
>>>> the
>>>> rains in question come at the end of a relatively long warm dry period.  In
>>>> this latter situation, the swelling ascospores cause the pseudothecia to
>>>> explode and the light-triggered release mechanism may be by-passed.
>>>>      The Cornell model was based on lab trials that showed ascospores
>>>> can infect in the same relatively short periods that Bill Mills had
>>>> initially described for secondary infections. Thus, the Cornell model will
>>>> trigger 'infected' before the Mill's MI model. Although NY has adopted the
>>>> 'Cornell model' because it is technically more correct, I still prefer the
>>>> modified Mill's table that was developed by Jones (although I do believe in
>>>> discounting night-time wetting, especially early in the season).
>>>>      Bill Mills developed his scab model by actually looking at what
>>>> happened to trees outdoors.  As a result, his model and the modified Mill's
>>>> table from Al Jones actually represent an integration of minimum infection
>>>> conditions AND spore numbers. Conidia are always produced in much greater
>>>> quantities than ascospores under conditions in commercial orchards.  Thus,
>>>> with conidia, large quantities arrive and infect leaves within 6 hr at
>>>> optimum temperatures.  If you artificially put large quantities of
>>>> ascospores on leaves, you also get infections within 6 hr at optimum
>>>> temperatures.  In reality, however, it takes some time for an economically
>>>> significant dose of ascospores to arrive on leaves in a commercial orchard
>>>> because there are relatively few of them. Mills and Al Jones therefore used
>>>> 9 hr as the minimal wetting period at optimum temperatures to account for
>>>> the fact that their data suggested it would require an extra three hours to
>>>> accumulate an economically significant
>>>  dose of ascospore as compared to conidia. (Some of my plant pathology
>>> colleagues my wish to quibble with these broad generalizations because I've
>>> skipped a lot of details and also done some "reading between the lines."
>>> Nevertheless, I think my general conclusions in comparing the two models are
>>> valid.)
>>>>      The Cornell model also provides only a yes/no response to
>>>> infection, whereas the original Mills table and the Jones version of the
>>>> Mills table still provides gradations of light, moderate, or heavy 
>>>> infection
>>>> based on duration of the wetting periods at various temperatures.  Again,
>>>> because ascospores are relatively limited in number in most orchards, it
>>>> makes sense to parse out the severity of infection for ascospores whereas
>>>> just the minimal wetting/temperature requirements are enough to trigger
>>>> conidial infections if conidia are present because conidia are either
>>>> present in large numbers or not at all.
>>  >>      By having information on light-moderate-heavy infection, one can
>> adjust one's on-site risk factors based on other details of the specific
>> orchard situation.  For example, in a clean orchard with trees just at green
>> tip, I would ignore the "light" Mills period and begin to worry only after
>> triggering at least a "moderate" Mill's period because there are so few
>> spores at green tip that the marginal conditions for a light infection
>> period will be unlikely to result in noticeable scab.  However, even in a
>> clean orchard, I would NOT ignore a light Mills period when trees are at
>> tight cluster or pink.
>>  >>      I hope others will chime in on what differences may be
>> incorporated into the Washington model.
>>>>>  Is anyone else on this list using Spectrum instruments to monitor
>>>>> weather and model disease? - I've had a 'Watchdog' for several years now,
>>>>> and yesterday had an anomaly, with complete disagreement and 
>>>>> inconsistencies
>>>>> between the three scab models -
>>>>>  The software uses models from Cornell, Washington State, and Mills
>>>>> (MI) - I'm used to Cornell being very conservative and WA being the 
>>>>> opposite
>>>>> - this event, Cornell indicated 'infected', WA 'none', and Mills 'heavy' -
>>>>> I've never modeled an event with Mills being 'heavy' and WA 'none' -
>>>>>  circumstances were such that we were cruising along in the lower 40'sF
>>>>> monday and then an overnight rain till 7AM tues morning  - a two hour dry
>>>>> period, followed by a rain, followed by the violent front (no damage here,
>>>>> but tremendous light show) - while that front was moving thru, 
>>>>> temperatures
>>>>> rose above 50*F for about 6 hours, peaking at 56*, before declining back 
>>>>> to
>>>>> the lower 40's again -
>>>>>  to add to the mystery, if I model tuesday, from the two hour dry thru
>>>>> the end of the event, I get the 'infected', 'none', 'heavy' analysis from
>>>>> the program - if I run the model from the start of the rainy event monday 
>>>>> so
>>>>> to include the rainy monday night/early tues thru the end of the event
>>>>> wednesday morning, the Mills model indicates 'light' infection (Cornell
>>>>> indicates 'infected', WA 'none) -
>>>>>  as a practical matter, at our stage of development, these
>>>>> temperatures, and specific schedule of the wet periods, I normally 
>>>>> wouldn't
>>>>> worry much about scab infection - but seeing that 'heavy' infection
>>>>> indicated from the Mills model is disconcerting -
>>>>>  dunno - any thoughts?
>>>>>  thanks,
>>>>>  David Doud
>>>>>  grower, IN
>>>>>  _______________________________________________
>>>>>  apple-crop mailing list
>>>>  --
>>>>  ************************************************************** 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
>>>>  _______________________________________________
>>>>  apple-crop mailing list
>>>  _______________________________________________
>>>  apple-crop mailing list
>> _______________________________________________
>> apple-crop mailing list
> --
> ************************************************************** 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
> _______________________________________________
> apple-crop mailing list

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