Re: Apple-Crop: For Discussion: Pesticide Applications Rates and Tree Row Vol...

[Duane Greene]

Hello,

   I have tried not to get into the TRV discussion.  However, we have 
had some rather good discussion among individuals working on the New 
England Pest Control Guide.  Glen has been a key player here, and in his 
presentation at the New England Vegetable and Fruit Conference he made 
some very good points. 

   I work with plant growth regulators, and as Dave Rosenberger pointed 
out this concept was born and developed because of variable results with 
chemical thinning.  Plant hormones differ from pesticides since their 
response is linear or curvilinear based upon dose applied.  The goal is 
to apply an appropriate amount of hormone (thinner) to get the 
appropriate amount of abscission, and the correct amount is somewhere in 
the middle or lower portion of the dose response curve.   The margin of 
error is not great so a mechanism is needed to apply an appropriate and 
needed amount of chemical to all leaves and fruit for proper thinning. 

   I had the privilege of interacting many times with authors of the 
two most-commonly cited papers on TRV, Dick Unrath ( Sutton and Unrath) 
and Ross Byers.  Both researchers did their work in the mid Atlantic and 
the Southeast.  Tree vigor was high and tree grew on semi dwarf 
rootstocks.  Terminal growth in many places was measured in feet not 
inches and trees were very thick. This was confirmed when I toured North 
Carolina orchards  with Dick in the 1980s.    Therefore, it is easy to 
see why they used the relatively high water volumes for a minimum.  
Trees look a whole lot different now.  Trees are smaller and they are 
more open.  Blocks now with a TRV of 100 gal/min are common.      

   All plant growth regulator researchers that I know use only TRV in 
developing data that leads to the recommendations that appear in our 
pest guides.  Initial screening and early observation of new plant 
growth regulators involves the use of dilute hand gun sprays.  However, 
once efficacy has been established and an appropriate amount of material 
is made available, all researchers on the east coast apply research 
sprays based upon TRV. 

   There have been discussions that the calculated TRV that is 
published does not wet the foliage.  Most of use use the published 
procedure for calculating TRV.  The major value of this is that it gives 
us a tree volume that we are spraying and it gives us a volume of water 
in which we put our hormone sprays.  This then gives us a number of 
molecules of hormone that we are applying in the volume of foliage and 
based upon efficacy data.  The molecules are distributed somewhat 
equally on leaves and fruit if the sprayer is calculated correctly.  

   This system is not perfect but I would prefer to have an imperfect 
system that appears to work reasonably well rather  no system.  I offer 
government as a modern day example.  Do we need to revisit TRV, as has 
been suggest, and how to calculate it more accurately on different 
systems?  That is a great idea.  However the topic of  TRV in the past 
has been spurned as either being too difficult or not terribly 
relevant.  Perhaps there is interest and this is a viable research topic 
that if revisited can provide information for more efficient and 
effective application and use of materials that we apply to our trees.

Best regards,

Duane     

  

Dave Rosenberger wrote:
Hi, Glen --
    1.  Yes, as a general rule, I do want growers to believe that, 
except for crop load adjustment, "the safest bet will be to apply the 
recommended amount of product/A regardless of tree size." The 5-10% of 
growers who actually grasped and properly applied TRV will continue to 
do so (at their own risk), whereas the rate/A recommendations will 
avoid losses for the other 90% of tree fruit growers and will also 
bring us into compliance with EPA label writing and, for the most 
part, manufacturer recommendations.
    2.  I agree that using a minimum rate/A of 150-200 gpa increases 
the safety of TRV recommendations, but I still go back to the fact 
that, after 20 years of hearing the TRV gospel, the vast majority of 
growers (and probably the majority of research/extension folks)  don't 
know how to make TRV work on large farms with a variety of tree sizes 
and spacings.
    3.  I'm not certain about leaf density on modern trees compared to 
old standards.  However, spur-type trees are relatively new, and there 
can be no argument that leaves are closer on spur-type trees than on 
non-spur types.  Also, large old standard trees, and even many mature 
trees on MM.106 or M.7 rootstocks tended to have umbrella canopies 
whereas the areas within the TRV in modern training systems tends to 
be more fully occupied with leaves and fruit.
    4. Concerning your question about why a large tree should need 
more captan than a smaller tree:  I don't disagree with your 
analysis.  However, my point is that our application systems (as 
currently used by most growers) are so inaccurate that the only way to 
cover the centers of dense trees in mid-summer is to use the full 
legal rates so as to over-apply the captan (or whatever pesticide) on 
the most exposed parts of the canopy and fruit and thereby ensure that 
we are getting enough applied to the interior parts of the trees and 
the backs of the fruit as we near harvest.  I'd be willing to 
compromise on my anti-TRV position if we used the concept only until 
about petal fall because complete coverage is relatively easy during 
the early-season.  However, for summer sprays (especially for 
sooty-blotch and flyspeck), the coverage issue becomes more critical 
and the fruit/wall in high density systems creates coverage problems.
    5.  Finally, I have not reviewed recent literature, so I might be 
wrong.  However, my impression is that virtually all of the TRV 
publications were generated using tree sizes/spacing/training that was 
common with MM.106 or M.7 tree sizes.  Has anyone actually 
demonstrated that the system works with conventional radial-fan 
sprayers used in high-density (at least 500 trees/A) of M.9's that are 
producing 1000 bushels/A?  Remember that most growers are spraying 
these high-density blocks on an alternate row basis because driving 
every row requires double the miles/A and at least 50% more time than 
it did to spray a block of trees on 22-ft spacings.

Say it ain't so Dave!
Do you really want to leave it at:
"Thus, for the majority of apple growers, and especially when using 
newer products, the safest bet will be to apply the recommended 
amount of product/A regardless of tree size."

You really advise apple growers to put on same amount of pesticide 
per acre to 23 feet tall 20 feet wide trees as 8 feet tall slender 
spindle?

I'm with you about reduced spray capture on slender spindle putting 
brakes on how far you can go with TRV, but using a minimum 150-200 
gpa threshold seems to address that.

I don't get the part about leaves being 4 times closer together than 
they used to be.  While canopies have shrunk I don't think the 
density of leaves has changed.  That generates question of then how 
do apple trees grow so many more fruit per unit leaf area than 30 
years ago.  My assumption is that dwarf apple trees spend less energy 
(and thus leaf area) growing wood.  Thus, a higher portion of the 
reduced leaf area is contributing to fruit growth.  Way out of my 
league here.

I guess I'm still stuck on the idea that if fixed rate per acre is 
needed for smallest trees, then it would seem to be under-dosing for 
much larger trees, or more likely, that dose needed for huge canopy 
volume trees is more than needed for smallest trees.  I'm willing to 
believe that the weirdness that comes out of quantum physics is 
actually really true because it happens in a realm beyond my ability 
to observe, but standing in an orchard I have a hard time believing 
that a block of giganto trees and dwarf trees need the same amount of 
pesticide, especially fungicides.  Insects move around enough that I 
could be hypnotized into believing that the same rate of pesticide 
applies regardless of tree size.  But laying down captan to make leaf 
surface inhospitable to a landing scab spore seems inherently related 
to the amount of leaf area per acre.
This all makes me wonder if/how different body size affects human 
pharmaceutical dosage.  
"People, I just want to say, you know, can we all get along?"  - 
Rodney King, 1992

- Glen


Glen Koehler
University of Maine Cooperative Extension
Pest Management Office
491 College Avenue, Orono, ME  04473
Tel:  207-581-3882
Email:  gkoeh...@umext.maine.edu
Web:  http://pmo.umext.maine.edu/apple/
Fax:  207-581-3881


-----Original Message-----
From: apple-crop@virtualorchard.net 
[mailto:apple-c...@virtualorchard.net] On Behalf Of Dave Rosenberger
Sent: Saturday, January 16, 2010 5:12 PM
To: apple-crop@virtualorchard.net
Subject: Re: Apple-Crop: For Discussion: Pesticide Applications Rates 
and Tree Row Vol...

Hi, Dave --
    "Intimidation" may by too strong a word, and I certainly have 
never felt any sense of intimidation concerning my expression of 
opinions or my selection of research projects.  However, I think that 
all of us are just a bit reluctant to back away from cherished 
concepts that we viewed for many years as points of progress toward 
common goals (i.e., IPM, minimizing pesticide use, environmental 
progress, etc.).  As a result, we may be too slow to admit when some 
of these strategies no longer work as intended.  I probably should 
not have use the PC terminology to express this concern, but there is 
some of that involved.
    Ultimately, there can be little doubt that universities are 
backing away from the kind of applied research that is needed to 
address complex problems in agriculture. That fact is clearly 
illustrated by recognizing that Andrew Landers' program is perhaps 
the only university-supported program in northeastern United States 
that deals with issues of spray deposition despite the fact that 
virtually all other research on agricultural pest controls (whether 
biological, biorational, or traditional pesticides) are ultimately 
dependent on effective methods for getting the "pesticide" applied to 
the target.


    I think public universities are the locus of origin and 
propagation of
much that has become "politically correct" in American culture, yet I
am surprised by the suggestion (at the end of Dave Rosenberger's useful
observations) that unspoken intimidation may now influence the content
of university publications on spray recommendations.
There could be no enterprise in which unbiased science is more
essential than in its application to commercial tree-fruit culture.

David Kollas
Kollas Orchard
Tolland, CT

On Jan 16, 2010, at 11:45 AM, Dave Rosenberger wrote:

    Tree-row volume is a complex subject that always generates widely
divergent reactions.  I'll add my personal perspectives to further
muddy the water.
    First, as I recall, the TRV concept was introduced by 
horticulturists
looking for a way to reduce variability in results when they applied
chemical thinners, and it helped them to meet that objective. 
However, sprays applied to adjust crop load are different than pest
control sprays because, with chemical thinners, there are significant
economic penalties both for applying too much and for applying too
little.  With pest control sprays, you may pay a bit extra for the
pesticides when products are over-applied, but you lose MUCH more if
 >>you under-apply and have a control failure.
Thus, the risk-benefit ratio for implementing TRV changes
significantly when one moves from thinning sprays to pesticide sprays
unless one assigns high values to the social merits minimizing
pesticide use, etc.
    Nevertheless, TRV worked pretty well for most pesticides when 
it was
first introduced. I think that to some extent, this occurred because
during the 1960s and 1970s we were in the habit of almost always
applying pesticides at far higher rates than were generally needed.  I
recall being told at the start of my career in the 1970s that as
scientists we needed to test products under the highest inoculum
levels possible so as to arrive at generalized recommendations that
would always work on commercial farms no matter how dire the
situation.  Given those conditions, applying pesticides with TRV rates
involved very little risk because the high rates that we were using as
a base allowed plenty of room for error without risk of control
failures.
     Several big changes over the past 30 years have made the 
generalized
formulas for TRV less reliable. Apple production statistics for NY
indicate that over the past 30 years we have doubled production per
acre, and at the same time we have probably reduced tree size by at
least 50% if not more.  Put those two together, and you will realize
that we are now growing apples at least four times closer together on
the trees than was the case when TRV was introduced. I'm not certain
how fruit-to-leaf ratios differ between old standard trees and trees
on M.9, but I suspect that we still need nearly as many leaves/fruit
as we did 30 years ago, so we are probably growing our leaves 4 times
as close together as we previously did. This creates problems for
spray coverage.  When I look at high-producing orchards on M.9
rootstock and envision the tree row as a two-dimensional plane, I see
many areas in the canopy that look like solid walls of fruit touching
one another with additional fruit located behind the front wall and
with additional leaves and fruit on the other side of the canopy.
 >>The only way to get enough product deposited on the back sides of the
fruit wall is to over-spray the front side and hope that enough fine
particles are blown around to the back side or that the chemical will
redistribute with rains.
    To take Jonathan's initial analogy of spraying houses of different
sizes, I would suggest that we can envision changes in canopy/fruit
density as follows:  Assume the 2500 square foot house has exactly the
same layout as the 5000 square foot house, but all of the studs are
just twice as close together in the smaller house.
The houses are all framed up, but have no siding or wallboard covering
the studs.  Now you must drive down the street and spray the houses so
that you have complete paint coverage over all surfaces on the
interior studs in both houses.  I suspect that you would find that you
need nearly as much paint for the small house as for the larger house,
in part because it will be more difficult to get the paint to
penetrate to the interior of the smaller house with its more closely
spaced studs.
    Another aspect of TRV that has always bothered me is the 
assumption
that the ratio of on-target versus off-target spray deposition is
equal for all tree sizes.  I suspect that for smaller trees,
especially in young orchards where trees have not yet filled their
spaces, we actually end up with more spray on the ground than on the
trees.  To go back to the house painting analogy, the difference in
paint required might be less than initially expected if the paint is
applied using a sprayer traveling at a set speed in front of the
houses. The smaller house will just end up with more paint on the
lawn!  Using smart sprayer to turn off the nozzles between trees can
help, but we are still using really crude methods to get pesticides
deposited on trees.  It seems logical that differences in deposition
efficiency could be so huge as to negate the validity of TRV
 >>calculations.
    Another major concern that I have about TRV is that, for most 
of the
fungicides introduced in the past 20 years, application of low rates
is known to speed selection for resistance.  In fact, I am aware of
several cases in NY where I am convinced that using SI fungicides at
TRV rates contributed to rapid development of resistance to SI
fungicides. This concern about resistance development is one reason
that some labels have statements indicating a legal minimum rate/A
that must be applied.
(Personally, I don't like to see minimum rate/A statements on labels,
but I can understand the rationale for having them.)
    Using reduced rates with new products is especially risky.
Pesticide companies have significant incentives for labeling products
at the lowest possible rate per acre that will be effective.  For most
products, I suspect that product pricing is based on "willingness to
pay" rather than on actual costs for making the product.  Thus, if my
new product is so good compared to competing products that growers
will likely pay $35/A for it, then I can maximize profits by keeping
the application rate just above the breaking point because I'm going
to get the same income regardless of whether the product is labeled at
1 oz/A or at 3 oz/A.  Labeling the product at lower rates also reduces
the contribution of pesticide residues on apples to my risk cup, so I
can label my product on more different crops.  As a result of these
factors, there is much less room for error in using new products
compared to older products like Guthion, Captan, and mancozeb
fungicides that seemed to work well with TRV.
    In summary, I still believe that TRV can be useful if it is done
carefully, and I like Dave Kollas's suggestion of actually checking
with water to determine what is required as a dilute base in your own
orchards.  Most growers, however, will not have the time or patience
to do that for blocks of different sizes. Thus, for the majority of
apple growers, and especially when using newer products, the safest
 >>bet will be to apply the recommended amount of product/A 
regardless of
tree size.  That suggestion runs counter to IPM philosophy and
initially may seem illogical vis-a-vis minimizing pesticide use. 
However, as outlined above, I think that we have good scientific
reasons for questioning the validity of the TRV formulas that were
developed 30 years ago, but it is not "politically correct" to remove
TRV recommendations from university publications. (Uh-Oh! perhaps that
last statement went a bit too
far?)


Lots of input on this one Jonathan.  It seems that some labels say
not to go below a certain rate per acre.  I am aware of at least one
case where a pyrethroid failed to control apple maggot.  I agree that
the OPs give more room for error.  It looks like pest management will
get much more precise as we get into "softer"
materials in terms of timing, monitoring and rates.

Art Kelly
Kelly Orchards
Acton, ME

--
************************************************************** 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/



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 >
Apple-Crop is not moderated. Therefore, the statements do not
represent"official" opinions and the Virtual Orchard takes no
responsibility forthe content.


--
**************************************************************
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/



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Apple-Crop is not moderated. Therefore, the statements do not represent
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--
Duane W. Greene
Department of Plant, Soil and Insect Sciences
Bowditch Hall
University of Massachusetts
Amherst, MA  01003
Phone: 413-545-5219
FAX: 413-545-0260
E-mail: dgre...@pssci.umass.edu



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