Rhode Island Apple IPM
May 17, 2011: Recorded Apple Pest Message in Print

Hi Fruit Growers,
This prolonged, wet weather could be very damaging. If it's been more
than 5 days since you've sprayed a fungicide I suggest you apply one
between showers. Fungicides to use between showers include Captan
(Captec) or one of the EDBC (Manzate, Polyram, Dithane, Pencozeb). The
SI fungicides (Rally, Inspire) need at least 30 minutes of drying to
be absorbed in the leaves and be effective - so save these expensive
fungicides for a dry stretch.

Don't worry about insects now - do worry about apple scab and spraying
fungicides! We are close to the end of apple scab primary season in
Providence & Washington County, but Newport County was just entering
full bloom on May 13th - so the apple scab is even more of a threat in
orchards in Newport County.

Below is an excellent review of diseases during extended wet weather
by Dave Rosenberger from Cornell:

"What follows are some rather lengthy comments on several disease
control concerns that have been raised by various parties due to rains
that are predicted to continue for the next several days, at least
here in the Hudson Valley. I've tried to stick to "facts" from
published literature (some of which I just finished reviewing), but
some of the suggestions are extrapolations from the best info that I
have been able to find. I'd be happy for any corrections or
discussion if you disagree with my perspectives or have additional
insights.

BLOSSOM-END ROTS: We are at petal fall in the Hudson Valley, so the
extended rains we are experiencing could provide ideal infection
periods for blossom end rots. I think that I last addressed this
issue at length in a 2005 article in Scaffolds that you can access at
http://www.scaffolds.entomology.cornell.edu/2005/050509.html#d2. Due
to current concerns, I have again reviewed recent reports on fungicide
trials in vegetable crops where researchers evaluated control of
Sclerotinia sclerotiorum on snap beans. (S. sclerotiorum causes most
of the blossom-end rot problems on apples in NY and New England, at
least so far as I can tell.) Those snap bean reports suggest that
while Topsin M is very effective against S. sclerotiorum (e.g., 99%
control), Flint usually gives only about 50% control and Vangard is in
the same ballpark as Flint. Nova (now sold as Rally) provided no
control at all.
I could not find any reports where Inspire Super or
difenoconazole was tested against S. sclerotiorum, but based on its
component chemistry, I would have to guess that Inspire Super probably
will not be much better against blossom-end rot than Vangard used
alone. I have no idea whether or not Vangard will control blossom-end
rot after infections have already occurred (i.e., does it have 72 hr
of post-infection activity as it does for scab?), but I would not
count on it. Vangard is generally viewed as having weak activity for
preventing scab on fruit (whereas it works fairly well against scab on
leaves), so I am not at all certain that it will work as well on
blossom-end rot of apple fruit as it did on snap beans. Since Vangard
is very active on Botrytis, I'm sure it will control the blossom-end
rot caused by Botrytis, but that pathogen is probably less of a
concern than Sclerotinia.
The bottom line is that Topsin M is still probably the best
product for controlling blossom end rot caused by S. sclerotiorum,
especially if one needs some post-infection activity (i.e., as for
Hudson Valley growers who may get their first spray window on
Thursday!). I think that Captan also provides adequate protection
against blossom-end rot on apples, but a week of cool cloudy weather
will make leaves exceptionally susceptible to captan injury (at least
in the Hudson Valley where we are in the middle of the spring growth
flush for terminal leaves). Thus, growers will need to be very careful
about tank mixing captan with other things that might enhance the
phyto potential of captan (e.g., nutritional sprays, EC formulations
of other products, etc.) Also, Captan will not provide an
post-infection activity against blossom-end rots whereas I suspect
that Topsin M does provide some post-infection activity.
The disadvantage of Topsin M is that it cannot be counted on
for controlling either scab or mildew, so growers must decide if it is
really worth the cost to add it to the tank just for control of
blossom end rot. It could help with control of flyspeck ascospores,
but flyspeck will also be controlled by mancozeb, Flint, Sovran, and
Inspire Super, and all of those will benefit scab control as well. As
noted in the 2005 Scaffolds article, I suspect that most of the
inoculum for S. sclerotiorum comes from broadleaf weeds in the
orchards ground cover (e.g., dandelion, etc.). Thus, orchards with a
lot of broadleaf weeds may be at greater risks than orchards where
growers have used 2-4D in autumn to eliminate dandelions and other
weeds in the ground cover.

APPLE SCAB ASCOSPORE DISCHARGES DURING PROLONGED RAIN EVENTS: Several
folks have asked recently about the pattern of ascospore discharge
during extended wetting periods. In the lower Hudson Valley, the
rains that started on Saturday night should have released the last of
the ascospores based on the NEWA model of ascospore maturity. If you
believe that model, then fungicide residues on leaves will have been
sufficient to take care of scab initiated by ascospores. HOWEVER,
there are two caveats: First, the folks at Biglerville reported today
that they are still getting a lot of scab spores in their discharge
tests with old leaves. (We did not run a test here as Fritz Meyer is
traveling out of state and we would not have been able to access dry
leaves anyway.) The PA report may or may not be relevant to how many
spores are really getting discharged in orchards because much of the
over-wintering leaf litter has disappeared in orchards, and spore
trapping with Burkard spore traps over many year/locations has shown
that lab discharge tests will continue to show ascospore releases long
after orchard spore traps stop catching spores. To me, the second
caveat is more important: no one can be certain at this point that
they have achieved 100% control of primary scab, so I consider all
orchards to still be at risk for apple scab during this wetting event
even if the ascospores are gone.
While it is true that peak releases of ascospores are usually
recorded at the beginning of wetting events (or as soon as wetted
leaves are exposed to light), that does not mean that nothing happens
during the 2nd, 3rd, or 4th day of a long rainy period. Both
ascospores and conidia continue to mature and be released during
subsequent days of multi-day wetting events (e.g., see the graphic in
Fig. C on page 261 of MacHardy's apple scab tome). Thus, growers who
lost their fungicide protection (i.e., had more than 2 inches of rain
since their last spray was applied) are still liable to get scab
infections occurring during the later stages of this prolonged wetting
period. Their options are to either sneak in a protectant spray of
mancozeb or captan between the rains or during the rains, or to wait
until the weather clears and then use something that has postinfection
activity.
To me the two choices for postinfection activity are Syllit or
Inspire Super. Inspire Super would be my first choice in cases where
SI-resistance is not a concern and/or most infections occurred within
the past 72 hr and therefore will be controllable with the Vangard
component in Inspire. Syllit may be a better choice where
SI-resistance is an issue (especially for scab-susceptible cultivars
like Macs) and where trees are at or past petal fall (because I don't
trust Vangard to control scab on fruitlets). Flint may also work well
if you are only looking for 48 hr of kickback, but frankly I don't
trust strobies to get folks out of trouble where postinfection
activity is needed. We have been concerned that Inspire Super is weak
on mildew, but mildew is of only secondary concern when we get this
much rain.

QUINCE RUST can be epidemic with prolonged wetting periods at pink or
petal fall. (The open flower petals may decrease risks of infection
during full bloom??) Quince rust especially benefits from
intermittent wetting periods such as we are having today and are
predicted to have through the end of the week. SI fungicides
generally give very effective post-infection control of quince rust,
so anyone applying an SI at the end of the week should come out OK
provided they get adequate coverage. However, Syllit will not control
rust and mancozeb will not provide post-infection activity. Thus, in
the Hudson Valley, if you need Syllit in an SI-resistant orchard to
get kick-back on scab, you may still need at least 4 oz/A of Rally to
get quince rust and Topsin M for blossom-end rot and ..... (chemical
salesmen are smiling!). (If I were targetting just quince rust, then
I would use Rally rather than Inspire Super because Rally is cheaper
and has a more proven track record against quince rust, although
Inspire Super has done well against quince rust in my trials).

CABRIO fungicide: Cabrio is labeled for scab and mildew on apples,
but I'm not certain that it really is very useful and BASF generally
does not recommend it (i.e., you will not find the apple label for
Cabrio on the CDMS website even though you can find it on the EPA
site). Below is what I just sent off to a consultant who inquired
about it:
So far as I know, Cabrio was labeled on apples primarily to
cover a shortage of Pristine that occurred several years ago. I don't
know how pricing of Cabrio compares with Pristine (presumably it
should be somewhat less expensive). The other component of Pristine
is Endura (boscalid), and the boscalid really adds nothing in terms of
controlling scab, rust and mildew on apples, so Cabrio should be just
as good as Pristine when applied at this time of year.
HOWEVER, Pristine generally has been no better than, and
sometimes less effective than Flint or Sovran against apple scab, so
there has been no impetus to use Cabrio for scab. AND, for summer
diseases, I suspect (but don't have data to prove) that the boscalid
component does play a role in the activity that we see with Pristine.
Thus, I would NOT suggest Cabrio as a substitute for Pristine in
late-summer sprays where growers want a long residual activity against
flyspeck and/or black rot. Also, summer diseases are not included on
the Cabrio label. Bottom line is that I see Cabrio is a bit of an
orphan in the apple market (unless someone can point to evidence of
activity that I have missed). I also suspect that BASF sees it this
way, because they really have not promoted Cabrio for early season
disease control on apples."

See you at Narrow Lane Orchard, 213 Narrow Lane, North Kingstown at
5:30 on May 19 for our second twilight meeting!!
Heather