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CRANBERRIES
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Calculating Percent Out-of-Bloom
(scroll down for a practice
exercise)
Percent out-of-bloom is monitored in cranberries
to assist in the management of the cranberry fruitworm.
It is good to visit 5 to 10 different random spots throughout a bed, counting
the blossoms and/or pinheads & berries on 5 or more consecutive uprights
at each location. The location and starting upright should be random
(don't pick the best spot, in other words). A good technique is to
stop after every 20 steps, or any number you predetermine, and beginning
with the upright closest to your last step. The more uprights and locations
in the bed you check, the more confident you can be with the result.
Formula:
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% Out-of-bloom =
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Total # of pinheads &
berries
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x
100% |
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Total # of pinheads, berries, flowers
and unopened flower pods
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Timing first spray using % out-of-bloom:
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Apply 1st treatment 7-9 days after 50% out-of-bloom
for Howes and Early Blacks, 5-7 days for Ben Lears and 3-5 days for Stevens.
Five days after the treatment, inspect 50 randomly picked berries/A (with
a minimum of 200 berries) for eggs. Follow guidelines in table below to
determine necessity of spray. If egg numbers trigger spray, spray ASAP.
If no egg is found, repeat berry inspection process every 3-4 days until
Aug. 20th.
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In the event of unusually warm or cool weather
during fruit set it may be advisable to shorten or lengthen accordingly
the interval between 50% out-of-bloom and the first spray.
Late Water (see the Maine
Cranberry IPM Guide) may effectively reduce fruitworm pressure. It
is possible that sprays can be eliminated for cranberry fruitworm, but
berries must be monitored for eggs throughout the fruitworm season as the
moths are very mobile and may move into your bed from external sources—namely,
from stands of wild cranberries.
TREATMENTS - MONITOR EGGS TO TRIGGER
SPRAYS (Difficult without a microscope)
As fruits set, begin inspecting 50 randomly-picked
berries/A (with a minimum of 200 berries per piece) for eggs. Follow the
guidelines in the table below to determine if a spray is warranted. If
egg numbers trigger a spray, spray as soon as possible. Otherwise, repeat
the berry inspection process every 3-4 days until egg-laying time has passed
by (around Aug. 20th). If fruitworm pressure is low through fruit
set, it may be safe to extend intervals between berry sampling dates.
TABLE USED (for all practices)
TO DETERMINE NECESSITY OF SPRAYING FOR CRANBERRY FRUITWORM
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Number of Acres
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Number of Berries Checked
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Number of Viable Eggs Needed to Trigger Spray during profitable
berry prices
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Number of Viable Eggs Needed to Trigger Spray during very low berry
prices
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0-5
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200-250
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1
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2
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6 or 7
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251-350
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2
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4
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8 or 9
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351-450
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3
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6
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10 or 11
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451-550
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4
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8
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for each additional 2 acres
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add 100 berries
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add 1 egg
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double the number
determined at left
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Practice Exercise
What is the % out-of-bloom after
checking these two uprights? The pinheads are numbered 1-4 just so you
can see them better in the photo.
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% Out-of-bloom =
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Total # of pinheads &
berries =
?
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| x 100% |
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Total # of pinheads, berries,
flowers = ?
and unopened flower pods |
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If you have comments or questions about this page,
contact Charles Armstrong at: charlesa@umext.maine.edu
Putting
knowledge to work with the people of Maine
