Volume 8, No. 19
August 1, 2000
Harvest Date Prediction
With just over a month to the start of McIntosh harvest, it is
time to consider the potential impact of the growing season to date on harvest
timing. There are several models used to predict McIntosh harvest dates, however,
the more recent model out of Cornell University seems most applicable to Massachusetts
orchards. (See 'Predicting Harvest Date Windows for Apples'ā Information Bulletin
221, Cornell Cooperative Extension.) The model uses full bloom date, plus the
mean temperatures for 30 days thereafter, to give a prediction for last date for
acceptable harvest of CA fruit (i.e., starch-index app. 6). Using full bloom date
(May 8) and the average temperature(s) for 30 days thereafter (May 9 - June 7)
at the UMass Horticulture Research Center, the Cornell model predicts September
22 as the last acceptable date for harvested McIntosh destined for CA storage.
Therefore, you need to back-up several weeks to anticipate the start of the McIntosh
harvest, depending on how long it takes to get your CA fruit picked. Note that
the model does not take into account the effect of growing season weather beyond
the 30 days after bloom, which we all know has some impact on fruit maturity.
Clearly, we have had below average mid-summer temperatures. This suggests delayed
maturity and -- all other things being equal -- good fruit quality. But bloom
was early, so all signs point to a 'normalā' or 'average' harvest window for 2000.
Now, all that being said, you must also look at various other fruit maturity characteristics
-- particularly color and starch-index -- to fine tune the start and end of McIntosh
harvest.
ReTain Application Timing
For those growers that use ReTain (Valent BioSciences Corp.)
on McIntosh as a harvest management tool, application time is rapidly approaching.
In fact, here is Dr. Duane Greene's most recent contribution to Valentā's weekly
'Harvest the Potential' Report (free by FAX or e-mail, call 800-323-9527):
"Cloudy conditions and persistent rain has characterized
the weather during the past week. Fruit continue to grow at a moderate rate.
Fruit size in monitored blocks of McIntosh, Delicious and Gala is 2.47 in.,
2.22 in. and 2.33 in., respectively, which is slightly smaller than fruit
size at the same time last year. We judge that the stage of maturity of apples
is similar to historical norms. Therefore, growers should plan to apply ReTain
on McIntosh and Gala between August 10 and 15. Summer pruning before application
is recommended on blocks destined to receive ReTain, to improve spray coverage."
Some other important points to keep in mind when applying ReTain
include:
- ReTain must be applied four weeks before anticipated harvest
-- if in doubt, slightly earlier is better than later
- ReTain should be applied dilute (i.e. thorough wetting of
fruit and foliage) and not be tank-mixed with other agricultural products
- ReTain application must include an organo-silicone surfactant
per label directions
- For best results, ReTain should be applied under slow drying
conditions - ReTain application should not be followed by rain or irrigation
for at least six hours
- ReTain should not be used on trees under stress
(Adapted from an article by Win Cowgill and Jeremy Compton, Rutgers Cooperative
Extension Plant and Pest Advisory Newsletter, Fruit Edition, July 25, 2000.
As always, read and follow label directions.)
Don't Give Up On Calcium
July's wet weather has kept many fruit trees growing quite
vigorously. Terminal growth is still active, creating a potentially strong 'sink'
for calcium in the trees. This sets up competition for calcium between fruit
and foliage so it may be particularly important to continue (or even increase)
foliar calcium applications as we approach harvest. The recommendation is to
apply at least two sprays of calcium chloride (78% CaCl2) at 3 to 4 lbs. per
100 gallons (dilute) at 4 and 2 weeks before harvest. Again, these calcium applications
are highly recommended this year to avoid disorders such as bitter pit, cork-spot,
and general storage breakdown. Note: Judicious use of summer pruning will also
help move more calcium into the fruit, particularly on calcium disorder sensitive
varieties such as Cortland.
European Descent
Foliar samples over the past (wet, cold) couple of weeks have
revealed only marginal increases in European red mite populations. Only a few
sections of a few blocks have exhibited signs of mite stress, and no monitored
orchards have seen need or opportunity for treatment targeting mid-season ERM.
Given the cool, wet weather of the past month, coupled with the general lack of
early-season mite pressure, it seems unlikely that many growers will face a pressing
need for application of a summer rescue miticide. However, if samples yield an
unacceptable ERM population (80% or more leaves infested), Vydate, Vendex, Kelthane,
Apollo, and Pyramite are all labeled for summer use. If a need is felt for summer
treatment, growers should keep in mind the risks and regulations (resistance development,
preharvest intervals, impact on predators) surrounding each of these materials,
discussed in earlier issues of Healthy Fruit and the 2000 March Message.
Weathering Heights
After nearly a month of sampling for invasion and damage of apple
maggot flies, it is apparent that this seasonās population is pretty light. In
fact, statewide levels of AMF capture on unbaited monitoring spheres haven't budged
from 0.5 AMF per sphere between our first sampling round (7/10-7/19) and our second
round (7/24-8/2). With the relative lack of pressure, AMF stings on fruit have
also barely hit the radar screen. So thus far, we have recorded less than 0.1%
damage in commercial orchards. We have no solid explanation for the light load
of invading AMF, but feel that two issues may be at play. First, although moist
soil is necessary to promote emergence of AMF, very wet soil may actually slow
adult emergence through evaporative cooling: yielding soil temperatures that slowly
build to the threshold necessary to trigger widespread adult emergence. Second,
the extreme cold and light snow cover during a few stretches in January may have
knocked down the overwintering AMF population, as AMF pupae overwinter in the
top few inches of soil and are highly prone to cold-related stresses in a winter
without the insulating snow layer. Taken together, it is likely that most growers
will enjoy reduced threat from AMF this season, allowing a greater interval between
AMF applications (3 weeks or more, depending on monitoring trap captures) and
further reduction in the rate of material (Imidan or Guthion) needed to control
the light AMF load.
Healthy Fruit
is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker
Wright, Arthur Tuttle, Wes Autio, Bill Coli, and Duane Greene
except where other contributors are noted. Publication is funded
in part by the UMass Extension Agroecology Program, grower
subscriptions, and the University of Massachusetts IPM Program. A
text version can be e-mailed to you if you contact
Doreen
York.
Please cite this source if reprinting information.
