I’ll add a bit to what Dan presented below: First, I doubt that anyone has
good evidence of captan causing or contributing to russet when it is applied
alone. In fact, in many field trials where impacts of fungicides on fruit
finish have been evaluated, captan applied at late bloom, petal fall, and first
has REDUCED russetting on fruit compared to unsprayed control trees. The
problems occur when Captan is included in a tank mix that includes surfactants
(either known surfactants added to the mix or those included in the
formulations of other products in the tank mix). The captan labels all state
something to the effect of “Avoid use of surfactants that cause excessive
wetting.” The reason for that warning is that captan is very toxic if it
penetrates through the cuticle and epidermis into plant cells. Surfactants
enhance the likelihood of such penetration. If you have 5 to 8 different
products in the tank at petal fall, who knows when you will reach the point of
“excessive wetting”?
In many situations, the first evidence of captan injury is leaf spotting, but
in some situations I believe (but cannot prove) that fruit russetting will be
induced at the same time. The reason that I (and probably no one else) can
prove that captan causes russetting goes back to the fact that such injury
occurs only when tank mixes are applied, and then one can always ask “Was it
captan or LI-700?" Or my insecticide, or the other fungicide in the tank, or
the strep I had in the same tank for fire blight? Or the proprietary
micronutrient that was applied either in the same tank or perhaps 5 days
earlier which allows it time to soften the leaves and fruit, making them more
susceptible to captan uptake and injury?
Concerning the fruit russetting observed throughout the northeast last year, I
suspect that most of it resulted from weather conditions during late bloom and
petal fall and would have occurred under any fungicide program. However, we
had a few cases of really severe fruit burn where captan interacting with other
products almost certainly contributed to the problem.
In my field trials in the Hudson Valley, we have multiple years of data
(including last year) showing that applications of mancozeb at weekly intervals
does a great job of suppressisng “natural” weather-induced russet on Golden
Delicious. (Captan applied alone would presumably suppress it as well, but we
use mancozeb because we need it to control rust diseases.) However, if you opt
for Captan to suppress russet, then you’re back to the tank mix/fruit uptake
problem.) Thus, based on my experiences in my field plots, I would avoid
captan from bloom through first cover, especially in years where there is a lot
of cloudy wet weather during this interval because cloudy wet weather allows
tissue to expand rapidly without developing much cuticle. Furthermore, I would
try to keep my trees well coated with mancozeb during the period from bloom to
second cover. Polyram is probably just as good as mancozeb, perhaps slightly
better for suppressing russet so long as rainfall between applications does not
exceed two inches. In a dry year, there will be no captan related problems
unless you really overdo surfactants in the tank mix, so if you like captan you
can stick with it in dry years.
****************************************************************
Dave Rosenberger, Professor Emeritus
Dept. of Plant Pathology and Plant-Microbe Biology
Cornell’s Hudson Valley Lab, P.O. Box 727, Highland, NY 12528
Office: 845-691-7231 Cell: 845-594-3060
http://pppmb.cals.cornell.edu/people/dave-rosenberger
****************************************************************
On Apr 2, 2014, at 3:46 PM, Daniel Cooley
<dcoo...@umass.edu<mailto:dcoo...@umass.edu>> wrote:
The evidence, whatever it is, is strong enough that Dave Rosenberger and Kerik
Cox are recommending that growers not use captan in sprays at petal fall and
first cover. From their article in Scaffolds (my bold):
"We are suggesting for the first time this year that apple growers avoid captan
in their petal fall and first cover sprays. Growers who choose to follow this
suggestion will need to avoid any prebloom applications of mancozeb or Polyram
that exceed 3.2 lb/A, because mancozeb will be needed as a contact fungicide in
the petal fall and first cover sprays. If mancozeb is applied at more than 3.2
lb/A in any spray, then the label does not allow for any use of mancozeb after
bloom.
"Our suggestion for avoiding captan in petal fall and first cover sprays is
based on the increasing complexity of tank mixtures applied at those timings.
Tank mixes at petal fall frequently include one or two plant growth regulators,
two or three fungicides, one or two insecticides, foliar nutrients, pH buffers,
water conditioners and/or spreader-stickers, and perhaps streptomycin for
controlling fire blight on late flowers. These complex mixtures increase the
likelihood that something in the mixture will enable the transport of captan
across the cuticle into plant cells where it will cause leaf injury and/ or
fruit russeting. The potential for injury from captan in complex tank mixtures
is especially high if the weather between late bloom and first cover is cool,
overcast, and wet. We observed or received numerous accounts of fruit and
foliar damage throughout the northeastern U.S. in 2013, but the frequency of
damage from captan has gradually been increasing over the past decade.
Therefore, in the interests of minimizing risks of crop damage, we believe it
would be wise to avoid captan in the petal fall and first cover sprays when
tank mixes are complex and fruit are most vulnerable to damage.”
---
Daniel R. Cooley, Professor of Plant Pathology
Stockbridge School of Agriculture
Fernald Hall 103
University of Massachusetts, Amherst, MA 01003
Office: 413-577-3803 | FAX 413-545-2115
http://people.umass.edu/dcooley
On Apr 2, 2014, at 2:24 PM, Arthur Kelly
<kellyorcha...@gmail.com<mailto:kellyorcha...@gmail.com>> wrote:
Is there other than anecdotal evidence as to Captan/Captec's role in the
russeting we saw in 2013? What about the effect of adjuvants such as LI700?
Also, who has experience with bloom thinning with ATS?
--
Art Kelly
Kelly Orchards
Acton, ME
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