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Volume 6, No. 2
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April 8, 1998
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Cool, Calm but Hardly Corrected
With a return to more normal spring temperatures, the
growth of all fruit trees has slowed. It might be better if
it stopped completely for about three weeks, but that's
highly unlikely. We are still well ahead of normal
growth.
McIntosh growth stages for various locations:
Ashfield 1/4" green
Belchertown 1/2" green
Northboro very early cluster
Sterling 1/2" green
Wilbraham 1/2" green to early cluster
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The Scab Skinny
Those growers who are not using some sort of eradicant,
including Benlate, Topsin-M, Syllit, Rubigan, Nova or
Procure, may want to keep a close eye on possible scab
development. The overall risk of scab is low, and in
orchards which were clean (no scab) last year then the last
week's infection period weather probably failed to start any
actual infections. Still, in high inoculum orchards,
particularly this year, last week could have started some
lesions. Normally, an eradicant by tight cluster will
suppress the few odd early lesions. But without eradicants,
these lesions may develop and produce some secondary
infections. Again, this should only be a problem where scab
was a problem last year, and no eradicants will go out for
another week or more.
Time Critical!
- Review mite strategy and get on it.
- Be ready for scab sprays, particularly places which
had scab last year.
- Fertilizer should be going on.
- Plant.
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The Great Polyram Debate
Up to this year, there has been a difference between
the way the New England Apple Pest Management Guide evaluates the
fungicide Polyram, and the way that the chemical companies feel it
should be evaluated. There have also been suggestions that Polyram
may be less toxic to mites, may promote a better fruit finish, or may
even control blister spot on Mutsu.
Probably this all started because Polyram is a somewhat, but not
completely, unique fungicide. It is an EBDC fungicide. So it's
related to mancozeb fungicides, such as Penncozeb, Dithane, and
Manzate. However, the common chemical name for the active ingredient
in Polyram is metiram, not mancozeb. It is chemically different. To
complicate things a little further, in 1989 or 1990 (it isn't clear
which) Polyram was reformulated.
The most obvious reformulation change involved making Polyram a
dry flowable as opposed to the old wettable powder. The reformulation
is undoubtably an improvement, at least from the users point of view.
Most wettable powders erupt from storage bags like with a volcanic
plume of fungicidal dust each time you open a bag or pour one into a
tank. The dry flowables stay in the bag until they are poured, and
then they go where you pour them. Whether this reformulation involved
other changes beyond making Polyram into a dry flowable is not clear.
The manufacturers have also argued that the refomulation improved
the coverage or the retention, or both, of Polyram. Whether this is
really true is less clear. However, it may explain the results of
some scab trials in recent years.
Originally New York, and as is often the case, New England rated
Polyram as somewhat less effective than mancozeb on apple scab. This
was based on trials conducted by Mike Szkolnik at Geneva (NYSAES).
The original data came from a 1982 test of redistribution, where he
showed that Polyram 80W 2 lbs/100 gal. was redistributed to new
leaves as well as Dithane M-45 80 W 1.5 lb/100 gal. with 1/2 in. of
rain, BUT with a second 1/2 in. the Polyram treatment was
significantly worse than Dithane. A year later, he looked at plain
spraying, not redistribution, showing Dithane M-45 80W 1.5 lb/100
produced a rating of 0.3, Polyram 80W 1 lb/100 a rating of 0.4, and
Polyram 80W 2 lb a rating of 1.3. The differences were not
significant, but suggested to Szkolnik that Polyram was slightly less
effective than the mancozebs. Anectdotal evidence from growers tended
to support this observation.
A recent review of fungicide efficacy tests against scab, looking
at tests from 1991 to 1997 showed that mancozebs and metiram
performed the same. In a total of 15 tests, some in combination with
SI's, or as part of a series with other fungicides, there were no
statistical differences between the two active ingredients. For
example, in one test a Dithane schedule produced 19% harvest scab
compared with 21% under a Polyram schedule, a non-significant
difference. In another test, Nova plus Polyram during primary season
produced 0.3% fruit scab at the end of June, while Nova plus Dithane
produced 0.0%, again a non-significant difference. In addition, our
own 1997 trial showed no difference in fruit scab at harvest in a
comparison of Dithane and Polyram applied on the same schedule at the
same rates.
This would apparently close the case, but some nagging doubts
remain. For example, in our tests the scab incidence early in the
season was signficantly different, and Dithane performed a bit
better. There is the early Szkolnik data. Most spray trials are
performed under ideal conditions, either spraying a tree until it is
drenched with a handgun, or using a low dilution with an airblast
sprayer. The arguement is that if a difference exists, it shows up
under extreme conditions and has to do with redistribution and
retention. However, the New England recommendations this year rank
Polyram equal to mancozebs in terms of scab control.
We reported last year in Healthy Fruit that "Polyram may be
somewhat less toxic to mite predators than Dithane, Penncozeb or
Manzate,but to what extent or under what conditions this is true
remains unclear." After a looking at many fungicides, Jan Nyrop of
Cornell reports that there is no difference between Polyram and other
EBDCs, at least on their Typhlodromus pyri predator.
It has been more difficult to track down who first thought Polyram
might manage blister spot on Mutsu or Golden Delicious. It would be
strange, because blister spot is a bacterial disease, caused by
Pseudomonas. However, metiram may be somewhat bactericidal.
There were no real reports testing Polyram on blister spot in the
publications I reviewed.
Polyram is a good fungicide. Nobody ever doubted that. The real
question was, when conditions were extreme, would Polyram do as well
as the other EBDC fungicides on scab. Based on the evidence to date,
it appears that it does.
Mites Might Have Dodged Early Oil
Given the brief window of opportunity for application
of a thorough oil program this year, we expect that many growers are
looking at options for an early-season miticide application.
Following are our recommendations for control of ERM by miticides,
which also appear in the 1998 March Message.
By June of 1997, 4 new miticides had been registered since 1995
for use on apples: Apollo; Savey; Agri-Mek; and Pyramite. The first 3
in this group are intended for use just before or just after bloom,
whereas Pyramite is intended as a rescue material for use in July or
August. In the 1997 March Message, we presented an extended
discussion of possible tactics for employing these materials. We will
not repeat such discussion here. Rather, we focus on 1997 results
from trials comparing these materials conducted by NEFCON in
Massachusetts, Art Agnello and Harvey Reissig in New York, Larry Hull
in Pennsylvania, Henry Hogmire in West Virginia, and Jim Walgenbach
in North Carolina.
In regard to the miticides themselves, studies in New York showed
that Apollo applied at petal fall performed considerably better (i.e.
provided season-long mite control) than Apollo applied at tight
cluster or at pink. This supports results of other studies reported
last year. Unfortunately, it's not legal to apply Apollo after tight
cluster. Savey at tight cluster gave mite control equivalent to
Apollo at pink and to Apollo plus oil at tight cluster. The bottom
line is that Apollo (1-2 oz/100) plus oil (1 gal/100) at tight
cluster is about equal to Savey (1 oz/100) at tight cluster or pink
in providing good to excellent mite control. In both West Virginia
and New York, Apollo at tight cluster without oil failed to give
season-long mite control, with plots requiring Pyramite by mid-July.
In Pennsylvania, Agri-Mek plus oil applied at pink gave slightly
better mite control than Agri-Mek plus oil applied at petal fall. The
petal fall timing was much better than the pink timing against
leafminers, however. In New York, Pyramite applied at petal fall gave
much better red mite control than when applied at pink. In North
Carolina, late-June applications of Pyramite, Vendex or Kelthane at
recommended rates reduced red mites over the next 5 weeks by about
90, 80 and 60%, respectively, and reduced rust mites by about 70, 70
and 50%, respectively. One general observation is that control of
two-spotted mites requires a higher rate of Pyramite than control of
red mites. Unfortunately, no 1997 study of which we are aware
directly compared 2 pre-bloom oil sprays with Agri-Mek, Apollo, Savey
or Pyramite.
Agri-Mek must be accompanied by an adjuvant (such as oil) to
facilitate its activity. Several adjuvants were compared in
Massachusetts, New York and Pennsylvania in 1997. Among horticultural
oil (such as Sunspray Ultrafine Oil), Sylgard 309, SilWet L-77,
Regulaid and LI-700, no adjuvant proved better than oil. Silwet was a
close second, with the others close behind. Oil is inexpensive but
does pose potential phytotoxicity problems if captan is to be used in
place of EBDC fungicides after bloom.
In 1997, some growers tried Silwet alone for mite control. In some
cases, it provided immediate knockdown of motile stages of pest
mites, much the same way that soapy water does. But it appeared to
have little or no residual effect. Thus, mites hatching a day or more
after application were not controlled.
Cyhexatin (formerly sold as Plictran) may be resurfacing under a
new name (Pennstyl) and may receive a label for use on apples, but we
do not expect that this labeling will occur until after the 1998
field season. Addition of such a chemical could be very good news for
apple growers, especially those who do not have populations of red
mites that were formerly (and still could be) resistant to cyhexatin.
As a final note, virtually all investigators who have worked on
control of mites on apples would place highest priority on biological
control of mites via predators as the best long-term solution to mite
management. Many growers who have constructed their pesticide-choice
programs so as to maximize the potential for mite predator buildup
find they no longer need to use any miticide except for pre-bloom oil
sprays. If it appears from early-season sampling or from previous
years' experience that some miticide in addition to pre-bloom oil
will be needed, then combined 1996 and 1997 information suggests that
Apollo plus oil at tight cluster, Savey with or without oil at tight
cluster or pink, and Agri-Mek with oil (or some other adjuvant) at
petal fall or a week after petal fall are the choices that will
provide best mite control with least adverse effects on predators.
Pyramite ought to be considered only as a rescue material for use in
late June, July or August. As strongly emphasized by Art Agnello of
New York, growers should do everything in their power to reduce the
likelihood of resistance to these new materials. Resistance has been
shown to occur in some orchards after only 3 consecutive years of
using Apollo or Savey (reports from other continents) and after only
4 consecutive years of using Pyramite (reports from Asia). Apollo and
Savey are very similar in their mode of action. If a grower plans to
use early-season miticides in a preventative-type program, then as
suggested by Art Agnello, year 1 could involve Apollo or Savey, year
2 Agri-Mek, year 3 Apollo or Savey, year 4 Agri-Mek and so on.
Plant Bug Particulars
In general, TPB adults do not become highly active
until the temperature rises above 70oF. We certainly had a
long period of such weather during the last week of March, but
temperatures since then have not stimulated further activity.
As expected, tarnished plant bugs have been present in most
orchards over the past week. However, trap captures on sticky white
rectangle traps remain low, even in orchards that are nearing tight
cluster. This suggests that even with the TPB present in the orchard,
activity within canopies is light, and it seems that thresholds for
treatment based on trap captures are still valid.
If insecticidal control is necessary, Guthion, Imidan, and Lorsban
remain the materials of choice. Pyrethroids (such as Asana, Ambush,
or Pounce) are usually more effective than any of the OPs and are
cheaper to buy, but they often prove more expensive in the long run
because of the negative effects on predatory mites. To recap a study
done in California in 1996, it was found that 7 months after a single
pre-bloom application of synthetic pyrethroid, enough residue
remained in the bark to kill 50% of the predators. 8
Leafminer Low-down
In orchards monitored with sticky red rectangle trunk
traps, no adult LM have been seen as yet. Last year, at this stage of
growth in McIntosh (1/2" green to tight cluster), half of sampled
orchards had exceeded 50 LM per trap, thus inspiring most growers to
treat for LM at petal fall last year.
Although the first LM adults may have emerged during the warm
weather of the last week of March, several factors must come together
before they will begin egglaying in the canopy. LM adults prefer to
move into the canopies during calm, warm evenings (55oF or
greater about an hour before dusk). Secondly, enough leaf tissue must
be peeled back to offer the LM oviposition sites. This is the case in
the earlier-developing orchards at present, and oviposition will
likely start this week.
Captures on trunk traps remain as the best existing way for
determining the need for pre-bloom or petal fall sprays against LM.
Based upon our most recent information, we recommend the following:
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Cumulative ABLM per trap
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Cultivar
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Silvertip to tight cluster
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Silvertip to pink
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McIntosh
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4
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9
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non-McIntosh
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8
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21
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Healthy Fruit is written by Dan
Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Karen Hauschild
except where other contributors are noted. Edited by Dan Cooley.
Publication is funded in part by the UMass Extension Agroecology
Program, grower subscriptions, and the University of Massachusetts
IPM Program. Please cite this source if reprinting
information.