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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Orchard<http://www.virtualorchard.net> and managed by Win Cowgill
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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/
--------------------------------------------------------------------------
The 'Apple-Crop' LISTSERV is sponsored by the Virtual Orchard
<http://www.virtualorchard.net> and managed by Win Cowgill and Jon
Clements <webmas...@virtualorchard.net>.
Apple-Crop is not moderated. Therefore, the statements do not represent
"official" opinions and the Virtual Orchard takes no responsibility for
the content.
