Island Apple IPM
May 24, 2011: Recorded Apple Pest Message in
Hi Fruit Growers,
This weather seems to go from bad to worse. Now in addition to
horrible apple scab weather we also have the threat of fire blight and
real difficulties thinning the fruit. In addition to this, Steve
Hoying from NY is saying Captan and carbaryl (Sevin) should not be
tank mixed this week because of problems with the captan damaging
foliage. When we get prolonged, cloudy weather, leaves don't develop
much cuticle and captan penetrates leaves and can burn. Sevin XLR
contains a surfactant that will make the captan penetrate the leaf
surface - and cause more of a problem. I don't know what to say! If
you are using Sevin XLR (and I understand the powder is not readily
available), I suggest using the least amount of Sevin XLR that will
thin the fruit: 1/2 pint per 100 gallons. This way you are applying
the least amount of surfactant.
As for fire blight, according to the models using our weather there
an Extreme threat May 27-29 to any apples and pears still in bloom.
The threat is High for May 24-26. These models can be found on Orchard
Radar at http://www.uri.edu/research/ipm/
Scab is still a huge concern! I found many active apple scab lesions
yesterday - and these are appearing before any lesions could appear
from the wet weather that started May 15. And plum curculio will
probably be very active during this warm, humid weather. Apply an
insecticide with your fungicide spray.
What follows is Mike Fargione's message from the Hudson Valley lab in
NY. His notes are from a meeting held yesterday in NY.
Fire Blight Alert
The forecast for this week leads us to believe there is the potential
for significant fire blight infections to occur if bloom remains in
apples and pears. The threat starts later today and continues
throughout the week. At this point, open bloom in our area probably
consists of rat-tailed bloom on 1-year wood, and blossoms opening on
newly-planted trees. At yesterday’s field meetings, Dr. Dave
Rosenberger suggested that a strep spray is warranted this week on
high-risk cultivars that still have bloom. Young trees that come from
nurseries where strep-resistant fire blight exists might benefit from
a mix of copper and strep if you have not yet applied copper to these
trees. The strep would do a better job than copper of controlling
local” strep-susceptible fire blight, but won’t control resistant
bacteria that came on trees from the nursery. Use low rates of
copper like 4-6 oz of COCS and not the higher rates listed in the Pest
Management Guidelines for pre-bloom. Leave out the copper if you plan
to try and harvest any fruit from these first-year trees.
Here are my notes from yesterday’s field meetings. Steve Hoying
Dr. Terence Robinson indicated that the next 7 days will be the
necessary apple chemical thinning window in much of our region.
During this period, growers should reduce application of thinning
agents below your “normal” rates for the following reasons:
1. Many blocks, including some perennial heavy-bearing varieties
like ‘Gala’, had moderate to less bloom due to 2 consecutive
years of heavy crops and some winter injury.
2. Foliage on trees is currently greater than normal for this
time of year and very succulent. More leaf area and soft tissue will
mean thinning chemicals will be drawn into the plant at
3. Predicted warm temperatures over the next week will mean trees
will respond more to the thinners.
4. Trees have been running a carbohydrate deficit since green tip
this spring and the deficit is expected to increase this week (see
updated carbohydrate models for Marlboro and Hudson). This means that
reserves of carbohydrates (i.e. energy source) in the trees are likely
to be reduced from “normal” and natural thinning or “June
drop” may be
greater than normal. (I am already seeing drop in some blocks, but we
expect to see significantly greater amounts once the trees undergo
some stress with the upcoming heat.
Based on the above observations, apple thinning recommendations for
our area include:
1. Wait as long as possible to thin in the hope you can determine
what level of drop will occur naturally and/or the result of your
petal fall thinner applications. You can get effective thinning out
to about 15mm king fruit size. At least wait until Wednesday or
Thursday, as the coming heat will cause fruit to start to
differentiate in size and you can get some handle on how much is
likely to stay and what will come off in the “June drop”.
2. Reduce “normal” thinner rates by 25% where blocks appear
have had good to snowball bloom and good pollination. Example: if you
normally use 10 ppm NAA, drop back to 7.5 ppm. Where blocks appeared
to have poor-moderate bloom, reduce rates further and use 50% of the
normal” rate or less. There are some blocks where natural June
will be sufficient and no chemical thinning may be needed this year.
3. This might be a year where NAA alone or carbaryl alone are
options in blocks of moderately hard-to-thin cultivars (Jersey Mac,
Paula Red, Aceymac, Spartan, Stamen) where you would normally combine
the two. Given the forecast for repeated wetting this coming week,
you might want to choose NAA alone because repeated wetting of
carbaryl may lead to excessive thinning.
4. Consider still using the combination carbaryl plus NAA or
Maxcel on hard-to-thin cultivars (examples include Cameo, Gala,
Honeycrisp, Fuji, Jonamac, Golden Delicious, Red Delicious, Empire,
5. Many growers prefer to use Maxcel instead of NAA on
small-fruited cultivars like Gala and Empire. Do not use Maxcel
without tank-mixing it with carbaryl as it is too weak a thinner on
its own. Just drop the rate of Maxcel by 25-50% depending on the
6. Do not concentrate the carbaryl this year to reduce residues
and thinning from rewetting. Example: if you have a 500 gallon tank,
only put in 1 pint per 100 gal or a total of 5 pints, regardless of
the number of “X’s” you spray.
7. This would be a year to use dry powder carbaryl to reduce the
greater possibility of phyto associated with the liquid formulations,
particularly the XLR+ formula. However, we learned yesterday that the
powder is in short supply or not available. Again, this is even more
reason not to concentrate the carbaryl.
8. It may also be wise to leave captan out of your fungicide
treatments in your next spray if you are thinning this week with
carbaryl, and certainly don’t tank mix captan with carbaryl this
9. You may not be able to see the results in time this coming
week before you must re-thin if you already applied carbaryl, NAA or
the combination at “petal fall”. In that case, reduce the
rate of NAA
or Maxcel to no more than 50% of your normal rate in your next
application. Some blocks thinned earlier may not need another
thinning application, but we won’t know that until we have a few
of heat to stress the trees. Warm night temperatures are the key
Hope this helps,