Volume 5, No.9 June 4, 1997Prepared by the University of Massachusetts Apple IPM Project Team in cooperation with New England Fruit Consultants and Polaris Orchard Management
While some of the later-developing areas of the state have only
progressed to 80% petal fall, the growth stage of McIntosh in
early to mid-developing areas ranges from 1/4" to 1/2"
fruit. Peaches are generally at shuck-fall or a bit later.
A spell of warm weather (several days in a row with temperatures in the mid-70s or higher) may still trigger a significant invasion of PC; leaving rapidly-developing fruit, even on the interior trees, particularly susceptible to PC injury.
We are still about 5 to 7_F below the average temperature this
season. This means tree development is slower, and some key pest
development is either slower or nonexistant.
On average, members of the UMass IPM crew have been examining
1500-2000 fruits per day across 48 commercial orchard blocks for
evidence of plum curculio activity. Each of these blocks is visited
and sampled every three days as part of a large experiment to
determine whether a correlation exists between captures of PC
in black pyramid traps and PC injury levels within the orchards.
Up to today, PC injury has averaged 0.4% across all sampled blocks,
and all of these blocks received a treatment against PC shortly
after petal fall. This level of damage (0.4% as of 6/4) is very
low relative to the past couple of years.
From ongoing studies of PC movement in some unmanaged orchard
sites, we have reason to believe that a significant proportion
of the overall PC population has yet to immigrate into orchards.
The reason behind this is that with the exception of last Friday
and Saturday (5/30 and 5/31), the weather has not been favorable
for PC immigration by flight. Warm spells, such as occurred last
week, are necessary to trigger invasions of PC from the woods
surrounding the orchard and to inspire egglaying activity within
the trees. In fact, in one early-developing, unmanaged site, PC
damage increased from 1% to 15% between last Friday and Sunday
(5/30-6/1).
In our judgment, the relatively cool weather pattern that has
been in place will probably translate to a long, drawn-out PC
season. Our extensive program of scouting will allow us to monitor
PC activity throughout the month of June, and we will keep you
updated as the PC season progresses.
The question of PC control now is whether the second application
against PC should be a whole-farm or a border row treatment. In
deciding between these options, an important consideration is
that the fruit at this stage of development are growing very rapidly,
and fruit may be partially unprotected if a well-timed protective
cover is not in place. Given the slow development of PC populations
within orchards, In next week's issue of Healthy Fruit, we will
include the specifics of the New York State degree-day model,
which aids in determining the end of the PC egglaying season.
Primary scab is practically over in all parts of the state. With the rains of the past weekend, the last significant ascospores of the season were released. Any infections from that release (given adequate wetting in your part of the state) should show up by the middle to end of next week. If you don't have scab by then, then you won't have primary scab this year.
Development among leafminers ranges from a few remaining egglaying
adults to a few scattered tissue-feeding mines, and everything
in between. As we are expecting with plum curculio, this appears
to be a drawn-out LM season. It is too early to make an accurate
assessment of potential LM populations, as LM in most areas of
the state are only at an early sap-feeding stage. Sap-feeding
mines will become more evident over the next week.
Growers who have concerns about developing LM populations should
sample interior fruit cluster leaves for evidence of sap-feeding
mines. As outlined in the 1997 March Message, our treatment thresholds
for first-generation sap-feeding mines under Massachusetts weather
conditions (dryer than some surrounding states) are 7 mines per
100 leaves for McIntosh and 14 mines per 100 leaves for non-McIntosh
varieties. These thresholds may seem conservative to some, but
judging from recent years' experience, LM have a great capacity
for rapid multiplication from one generation to the next. In other
words, even a relatively small number of first-generation mines
often translates into a much greater number of mines in the subsequent
generation. These thresholds for treatment represent our best
estimate from over 10 years of accumulated data.
Several orchards scouted by Polaris Orchard Management are already
at 15-25 mines per 100 leaves, which is beyond the threshold which
warrants treatment. If a post-petal fall treatment against first-generation
LM is necessary, most areas of the state still have time this
next week for an application of Provado or Agrimek; applications
should probably not occur beyond 1/2"-2/3" fruit.
In blocks receiving only oil as the pre-bloom treatment for mites,
some adult ERM and first generation eggs can be seen. However,
the numbers at this point remain very low. No adult ERM or eggs
have been observed in blocks which received a pre-bloom treatment
with either Apollo or Savey.
Under cool weather conditions, ERM populations tend to build slowly,
but growers intending to use Agrimek for leafminer and ERM control
ought to make the applications before the leaf tissue hardens
off, to allow proper penetration of the chemical. There are still
several days remaining for such treatments to occur.
In the May 14th issue of Healthy Fruit, we briefly discussed
the progress toward registration of Pyramite as a summer-use miticide
on apples in Massachusetts. This chemical represents a reasonable
replacement for Omite; although more harmful to mite predators
than Omite, it is less toxic to these predators than Carzol. As
mentioned previously, Pyramite has received federal approval for
use as a summer miticide on apples. However, registration in Massachusetts
is turning out to be more complex than we had initially thought.
Pyramite represents a new class of pesticide, which commands the
attention of the entire Pesticide Bureau during an upcoming meeting.
Thus, the registration process cannot be resolved by a conference
call as we had previously thought. We are hopeful that the registration
can be cleared by some time in July, and we will keep you posted
on the progress.
A fair number of rosy apple aphids have been observed on Cortland
and Gravenstein over the past week. Cultivars like Cortland, Gravenstein,
Ida Red and Golden Delicious are especially susceptible to RAA
damage, and should be considered for treatment with Lorsban, if
necessary.
Pear psylla nymphs have progressed into the hardshell stage in
some of the earlier-developing areas of the state. Sites which
have not yet received treatment against psylla are developing
significant populations and are showing accumulation of honeydew
on foliage. In orchards where an application of Agrimek against
pear psylla is being considered, this week is likely the time
in which these treatments should occur. In orchards where psylla
numbers are low (less than 1-2 nymphs per leaf), the application
can be delayed another week without any major problems.
In last week's issue of Healthy Fruit, we incuded a brief outline
of plant bug management strategies on peaches. Because of the
omission of the punchline, we are reprinting that discussion in
its entirety.
Shuck fall is the time to pay particular attention to signs of
attack by tarnished plant bug, oak plant bug and hickory plant
bug. Feeding by these insects peaks between shuck fall and when
the fruit reach 1/2"-3/4" in diameter. It is important
to protect fruit at this stage against 'catfacing' injury caused
by plant bugs. Research has shown that either Guthion or Imidan
alone are at best 50% effective in preventing plant bug injury.
Therefore, we suggest use of a full rate of Guthion or Imidan
in conjunction with a one-third labeled rate of a pyrethroid such
as Asana, Ambush or Pounce. We feel that because of the tendency
of pyrethroids toward high absorption into and slow release out
of the bark of the trees, the one-third rate of pyrethroid offers
a good compromise; extending the residual effects of the chemical
while limiting the well-known destructive effects against mite
predators. If mowing is planned in blocks of peaches, it is important
that an active protective insecticide cover be in place at the
time of the mowing. This will limit the effect of plant bugs,
which are numerous in the groundcover, when they are pushed into
the canopies by mowing.
As peaches leave shuck split, brown rot managment should change.
While managment during around bloom to shuck split, and during
the final stages of ripening, can be critical to brown rot control,
the time from pit hardening to early ripening is less critical.
Peach fruit are more resistant to brown rot during this period.
Last year, the fruit team did a trial on peaches at the HRC which
eliminated or reduced fungicides during this period. There was
no difference in the amount of brown rot regardless of whether
we applied 5 fungicides from shuck-split to harves, or only two
fungicides over that period. If we continue to have wet weather,
don't eliminate fungicide sprays after pit hardening. However,
a couple of applications over that period, even during wet weather,
should be adequate.
A far more critical period occurs when the fruit starts to color
and ripen. At that point, consider using the newer SI fungicides
labelled against brown rot on peaches: Indar, Elite and Orbit.
While these fungicides are pricey, they are also very effective.
To quote from Wayne Wilcox, who has done several years of trials
on these fungicides,
"Indar, in particular, has provided outstanding control of
brown rot for the last 3 years in our sour cherry trials in Geneva,
even when we inoculate fruit and really turn up the disease pressure.
For instance, under the most severe evaluation regime last summer,
80% of the unsprayed fruit were infected; fruit sprayed with 2
oz/100 gal of Nova had 59% infection; fruit sprayed with 2 lb/100
gal of captan had 25% infection; fruit sprayed with 12 oz/100
gal of Rovral had 19% infection; and fruit sprayed with 0.8 oz/100
gal of Indar had 3% (!) infection. ...Indar is also two or three
times as active as Orbit in lab assays of active ingredients,
although these assays are not always perfect reflections of what
happens in field."
In addition to being very effective, Indar, Elite and Orbit have
either a 1 (Indar) or 0 days preharvest interval. The goal of
most peach growers in Massachusetts should be to supply as ripe
and rot-free a peach as they can. These fungicides, applied as
needed around harvest, are probably the best option for this purpose.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, and Wes Autio, except where other contributors are noted. Final copy is 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 source if reprinting information.