/\42-l_ancaster Farming, Saturday, December 28, 2002
Grape Disease Control Update
Wayne Wilcox
Dept. Plant Pathology
Cornell University
New York State
Agricultural Experiment
Station, Geneva
Time for the annual review of new
cvelopments and various options on
..e disease-control front. As always. I’d
ke to acknowledge the outstanding
i am of grape pathologists here in Ge
.,' va, including faculty colleagues (D.
.adoury, R. Seem), research techni
mns (Duane Riegel, Judy Barr), and
laduate students and postdocs becom
ig too numerous to mention, all of
hose research efforts are the bases for
lost of the following.
Fungicide Changes
And News
1. Benlate cancellation. As many
now. Benlate is history. Worldwide
lanufacture halted in 2001, sale and
istnbution of product remaining m
le “pipeline” will be allowed through
te end of 2002. All registrations have
<cen cancelled, although it still is legal
use whatever product is on hand,
i cording to label directions. EPA “ex
cels” that use of such product will end
i- 2003. and is seeking comment on its
iroposal to revoke residue tolerances
ihereby making any residue in fruit or
'i me illegal after a reasonable length of
line). So, use what you have, but don’t
ockpile. Benlate is a minor fungicide
i >r N.Y. grape producers, used primar
b to protect major pruning wounds
>;ainst Eutypa. An application to reg
ler a closely-related benzimidazole
ungicides (Topsm-M) for use on
i apes is currently being considered by
■ ‘ le EPA.
2. Phyt, Aliette, and phosphorous
ProPhyt (potassium phosphite) is
formulation of phosphorous acid
"A) that is now labeled by the EPA to
mtrol downy mildew on grapes (N.Y.
gistration is still pending, but may be
rthcommg by summer). It does not
mtrol any other major grape disease,
arious formulations of PA have been
ed for approximately 15 years to con
ol downy mildew in Australia, and 1
apeatedly have gotten excellent results
dh several different formulations (m
-uiding ProPhyt) in m\ own trials,
en under very high pressure.
PA provides good post-infection con
ol of downy mildew, but because it is
ghly mobile m the plant, the Aussies
■intend that it has only a few days’
nrth of residual (protective) activity
fore it gets shipped down into the
mis Thus, they tend to spray it after
infection period has occurred, tank
xing with a traditional protectant
ich as manco/eb or copper) to pro
le forward protection against the
\t one In my own trials. I’ve applied
at 14-day intervals without any sort
tank mix and obtained virtually
iipletc control every year, even in
i ry wet seasons such as 2000, where
» arly 70 percent of the berries on uns
layed vines became diseased. How
's er, I haven’t scrutinized these trials
> determine just when the various in
cctton periods occurred with respect to
he timing of applications.
PA is so popular m Australia because
t is quite cheap there (just a few dol
ors per acre). Since ProPhyt is not yet
sold in NY, I don’t know what the
price will be locally (probably more
ihan in Australia!). If they are priced
light, this and other PA formulations
that may come along could certainly
find a place m eastern vineyards, par
ticularly if an otherwise-desirable dis
ease management program is weak on
downy mildew control. They’re worth
getting some experience with, provided
they make economic sense. (A note on
ates The ProPhyt label that I’ve seen
pecifies a concentration of 0.3 percent,
but this assumes a sufficient water vol
ime for complete coverage. Thus,
'.e’ve used 1 2 pints per acre prebloom
+(assummg a spray volume of 50 gal/A
bir complete coverages-) and 2.4 pints
,ier acre postbloom -(-(assuming 100
tal/A spray volumes-).
Ahette is a product that has been
■round for many years, but just re
ceived registration on grapes last sum
ner. It breaks down into PA once
prays have entered the plant, so ba
ically does the same thing as PA pred
icts but at a much higher cost (about
AO-50 per acre at the recommended
ite for grapes) Patent issues protected
Miette against cheaper PA products in
lie past, but the patent has now ev
-11 ed
Nationally, there are additional
inducts containing PA that are being
Id as nutritional supplements or
Sant condilioneis." without claims
their disease control activities ()l
irse they’re etlcctiye nevertheless
ic such product that we worked with
t year is Prudent Plus, a mixture of
is labeled for powdery mildew control
as Nutrol), and various organic com
pounds that are claimed to improve
plant growth and health. In our trials
last year, treated vines were virtually
free of downy mildew and powdery
mildew control was fair to good (better
than Nutrol, worse than conventional
fungicides).
3. Messenger. Messenger is a unique
and interesting product now registered
for control of grape diseases. It is a
nontoxic protein that stimulates natu
ral defense responses in some plants,
thereby providing variable levels of re
sistance to disease-causing organisms.
The only problem is, there is no con
vincing evidence that this occurs in
grapevines. On the contrary, such an
“induced resistance” response is notori
ously difficult to elicit in grapes, al
though many people (including a grad
uate student in my own program) have
tried to do so using various techniques
and products. Furthermore, I have ob
tained poor disease control in previous
grape trials where Messenger has been
used without additional fungicides,
however, these were conducted a few
years ago and it’s possible that the for
mulation has improved by now. Results
from several grower demonstrations
that I helped evaluate last year in coop
eration with a juice grape processor
could best be described as “inconclu
sive ” Although my experience with the
product is limited, it is not consistent
with some claims in recent advertising.
Those interested in the product may
wish to evaluate it for themselves on a
limited, trial basis.
4. Serenade. Serenade is a product
whose active ingredient is a soil bacteri
um (Bacillus subtiilis), which is regis
tered for biological control of powdery
mildew and Botrytis In two trials last
year (light disease pressure) we got
good control of powdery mildew when
Serenade was rotated with Sovran on
both the hybrid variety Rosette and on
Concord. In a Botrytis trial m 2000
(moderate pressure), four applications
of Serenade alone (no other fungicide)
provided zero control of that disease.
We’re continuing to evaluate it this
season. Limited experience causes me
to still view it as an experimental prod
uct: on a commercial crop, I’d be more
comfortable experimenting to control
powdery mildew rather than botrytis. A
formulation being sold in N.Y is certi
fied for organic production.
5. Other “alternative" products for
powdery mildew. As discussed last
year, a number of non-traditional prod
ucts have
been register
ed recently to
control pow
dery mildew
on grapes
They work, to
variable ex
tents, but it
helps to un
derstand why.
Powdery mil
dew (PM) is
an unusual
disease, since
the fungus
that causes it
lives almost
entirely on
the surface of
infected
leaves and
berries (the
powdery stuff
you see when
control breaks
down). Thus,
it is “naked”
and subject to
(temporary)
eradication
following top
ical treatment
with a range
of products
that don’t af
fect other dis
ease-causing
fungi, which
do their dirty
work down
inside the
plant tissues
where they’re
protected
from such
treatments
Some sueh
products drt
listed below
• IN nl ro 1
(nionopotdssi
uin pho s -
ph.ite) We \e
been working
with this diKil
purpose m<i
leruil (lolioi
nutrient plus powdery mildew fungi
cide) every year since 1996, with mod
erate results. In greenhouse tests, we’ve
found that Nutrol provides no signifi
cant control when applied before plants
are inoculated with powdery mildew
spores. In contrast, it provided signifi
cant control when applied within 3-7
days after exposure to the spores, i.e.,
when applied directly to the developing
PM colonies.
This scenario suggests that Nutrol
should be more effective when applied
relatively frequently (repeated knock
downs), rather than relying on residual
protectant activity between sprays. In
deed, we’ve gotten significantly better
control in two seasons of fieid trials
when applying 4 Ib/A every 7 days
rather than 8 Ib./A every 14 days. I
strongly suspect that this same general
principle (one-shot knock-down against
young colonies, with little subsequent
protective activity) will apply to most
of the ’’alternative” PM control prod
ucts. Thus, they may need to be applied
more frequently than many traditional
products.
• Kaligreen, Armicarb 100 (potassi
um bicarbonate). We haven’t worked
with Kaligreen, but Armicarb 100 has
performed similarly to Nutrol in field
trials. Photos in the trade press show
ing dead PM fungus on treated plants
also is consistent with the activity we’ve
seen from Nutrol (topical, eradicative
effects with no evidence of residual
protectant activity).
• Oxidate (hydrogen peroxide). Reg
istered for control of powdery mildew
and Botrytis. We haven’t worked with
it. I believe the claims for PM control,
but doubt those for Botrytis (see above).
Will probably require frequent applica
tions.
Finally, remember that the activity
of these topical materials is entirely de
pendent upon their contact with the
PM fungus. Don’t waste your time and
money if you can’t provide thorough
coverage.
6. Strobilurin fungicides These ma
terials (Abound, Sovran, Flint) have
been discussed at length for the last two
years. Thus, just a few updates and re
minders:
• The “strobies” are retained pri
marily in the waxy cuticle of treated
leaves and berries. Thus, they are excel
lent protectant fungicides when applied
before an infection period begins but
have only limited postinfection activity
against most diseases (can’t get down
into the deeper tissues where the fun
gus gets established). Although they
t
'J
appear to have additional postinfection
activity against powdery mildew
(which lives mostly on the surface, re
member), over-reliance upon such ac
tivity increases the risk that the fungus
will become resistant to these materials.
• Resistance development is a very
real and serious threat. Although no
body understands why, it appears that
the risk and speed of this happening
may be significantly different for differ
ent disease-causing fungi. For instance,
several specific diseases on grasses and
grains, cucumbers, and melons can no
longer be controlled with strobies in
some production regions, after only a
few years of use. In contrast, similar
problems have not yet surfaced with re
spect to control of powdery mildew on
grapes, despite considerable worldwide
use, although there have been some
overseas reports of problems with
downy mildew. These products still
work for us, but there’s no guarantee
that will continue indefinitely. Because
of their current importance to produc
ers throughout the Northeast, they
should be used conscientiously in order
to reduce the probability of resistance
developing, so that they will continue
to be effective.
• The only sure-fire way of reducing
the risk of resistance is by reducing the
number of sprays applied. Use the stro
bies when they’re really needed, but
don’t overdo it. The seasonal limit for
wine grapes is four applications, but
two or three is better. Juice grape grow
ers may make up to three applications
per season, but they should be sure to
rotate with other fungicides to control
the two mildews and black rot, even if
they’re only applying two or three such
sprays in total. And trying to “put out
a fire” with these materials if disease
gets out of hand is just asking for trou
ble. This is a simple numbers game: the
more fungal individuals that are pres
ent, the greater the chance of selecting
a resistant one
when you spray. COMPLETE
• In addition to
the numbers game
cited above, recent
research suggests
that resistance is
more likely to de
velop when strobies
are applied to a
growing fungus
(i.e„ postinfection)
rather than in a
protectant mode
which prevents
spore germination
and infection to
begin with. Other
than avoiding de
liberate postinfec-
tion applications, this means that ex
cessive spray intervals (greater than 14
days) also should be avoided. For pow
dery mildew, in particular, almost
every day in the late spring and sum
mer is a potential infection period (rain
not necessary, temperatures very favor
able). Thus, whenever a new (uns
prayed) leaf emerges after a given fun
gicide application, the next spray will
be “reaching back” to provide postin
fection control of whatever mildew may
have started after that leaf emerged.
Thus, the longer the spray interval, the
more infections that may have occurred
and the longer the necessary reach
back activity will be.
• Finally, consider these factors but
keep them in perspective. The sky isn’t
falling. These materials do work. But
be responsible and keep it that way.
7. Mancozeb and mites. This has
been talked about quite a bit the last
few years. Trials supervised by Jan
Nyrop and Greg English-Loeb in the
Entomology Department have consis
tently shown that fungicide programs
that include regular mancozeb sprays
will reduce the level of predatory mites
(those that eat the spider mites), by an
average of about 50 percent relative to
programs where captan was substituted
instead. In a few cases, this encouraged
the buildup of spider mites, but not in
the majority of trials. In an experiment
last year, there was no effect on preda
tors when mancozeb was limited to two
sprays prior to bloom.
These effects are real. As with so
many things, the risk (incompletely de
fined) and benefits (broad spectrum
and economical disease control, 24 hr
REI) need to be balanced. How to, spe
cifically, is a personal decision. My feel
ing is that mancozeb still has a place,
but that it should not be used indis
criminately. We’re still working on try
ing to supply you more specific details
than that.
AUCTIONEERING SERVICE
PUBLIC AUCTION
Saturday, Jan. 4,2003 @ 9:ooam
HUGE BUILDING SUPPLIES AUCTION
DIRECTIONS: Fiona Harrisburg travel north on
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VEHICLES
1840 Cub Cadet riding mower. 50" deck, full hydrostatic
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Pickup loads ot Flea Maiket items welcome the day
of the auction Call TB tor moie info
TB is open for regular business Mon, Tues, Thurs, &
Fri. 8:00 to 5:00, Wed. & Sat. 8:00 to 12:00
Auction Note; Call 717-444-7230 for auction informa
tion 2003 Auctions 2/1, 3/1. 4/5, 5/3. 6/7, 7/26, 9/6,
10/4, 11/1. 12/13 all stall at 9 00am
Owner: TB Lumber, 717-444-7230, RR I Liverpool
PA - AY-00022 3L
TERMS: Cash or good PA Check oi ciedit card with
2 3 r { accounting tee Matcnal must be lemoved liom
site h\ 1/0/03 Not lesponsihle (oi lost oi stolen items
Olhci teims given Ihe da\ ol auction \ll items suh|ecl
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KENNETH E MASSINGER NEIL A COURTNEY
RR 02. Box 985 R D #1 Box 239
McClure, PA 17841 unit Richfield, PA 17086
(570) 658-3536 43M (570)539-8791
AU-001532-L AU-002651-L