Fire blight prevention respray dates

Background Information for this page
Return to Apple list for Easthampton MA
Weather data for Easthampton MA.  Forecast values begin August 3, 2017
See Eastern Fire Blight model and Cougarblight model tables for details of daily infection risk ratings.
        This table has two uses.  The PERCENT of BLOOM VULNERABLE column gives a rough high-end estimate of the total percent bloom at risk for a fire blight blossom infection on each date.  That percentage is the portion of bloom that opened early enough to accumulate heat units for fire blight infection, yet opened late enough to have not yet reached petal fall before the infection period.   Values assume no antibiotic has been applied.  Values are high-end because they assume high portion of late cultivars in the orchard, that rain occurs after all heat units have accumulated, that flowers only reach petal fall at very end of the day, and that flowers remain fully vulerable until petals drop.  While estimates are at the high end, they give an indication of what percentage of the total orchard blossom population could be at risk in a mixed cultivar block.  For managing fire blight it is better to be safe than sorry as once fire blight gets established, damage can spread rapidly and eliminating it can be time consuming, expensive, and difficult to achieve.
        You can also use this table to estimate need for second or third antibiotic applications to prevent fire blight.  This table estimates how many flowers open on and after each potential antibiotic application date.  Flowers opening after an antibiotic spray are not protected.  In order for fire blight blossom infection to occur, newly opened flowers require time to a) get inoculated with fire blight bacteria carried into the blossom, and b) enough time after inoculation for heat units to for enough bacterial reproduction to cause infection if wetting carries bacteria down into nectaries.  This table estimates if and when flowers opening on a date will accumulate enough heat units followed by wetting to make blossom infection possible.
     Percent of Bloom Opening estimate assumes mix of early and late blooming cultivars (e.g. rom Gingergold to Honeycrisp).  Dates labeled "Late bloom only" are after petal fall for most culitvars, but when young trees and cultivars with late "secondary" bloom may still have open bloom. 
 "X" = Flowers opening on this date reach petal fall and are no longer susceptible to blossom infection before
they accumulate enough heat units for infection to occur.
DEADLINE FOR RENEWED PROTECTION if there is a Fire Blight blossom infection period while flowers opening on spray date are suseceptible.
"none" = models estimate no infection expected on any of the days that blossoms opening on this day remain open.
 If infection date is before "End of Susecpitibility" date, protection is recommended.  If infection date and "End of Susceptibility" are on same day, risk depends on whether infection period begins before petal fall.
Bloom percentages based on hypothetical orchard with range of early and late blooming cultivars.  Latest date for newly opened flowers is May 16
Open Blossom Dates
(dates extend beyond McIntosh Petal fall date to account for late blooming cultivars).
High end Estimate:  PERCENT of BLOOM VULNERABLE to a blossom blight infection period on this date. Rough estimate for
Percent of Bloom
Opening on Date in 1st column

(Number in parentheses is total % bloom opening AFTER this date).
New Blossoms could become Susceptible
= by end of this date flowers that opened at beginning of date in 1st column have accumulated enough heat units for FB infection.  Probably more realistic that flowers become susceptibile on the following day.
End of Susceptibility
= estimated end of suseptibililty for blossoms that open on date in 1st column.
Eastern Fire Blight Model CougarBlight - Category I:
No active FB within one mile for last two years.
CougarBlight - Category II:
FB active within one mile of orchard within last two years, but no currently active infections.
CougarBlight - Category III:
FB symptoms currently visible in the orchard or within one mile.
possible early cultivar
King Bloom: April 28 
no infection 11%  (89%) April 29 May 4 none none April 30 April 30
McIntosh King Bloom:
Sat, April 29 
no infection 10%  (80%) May 1 May 6 none none May 1 May 1
Sun, April 30  no infection 4%  (76%) May 3 May 6 none none none none
Mon, May 1  no infection 6%  (70%) May 4 May 8 none none none none
Tue, May 2  no infection 7%  (63%) x May 10 x x x x
Wed, May 3  no infection 3%  (59%) x May 11 x x x x
Thu, May 4  no infection 5%  (54%) x May 12 x x x x
Fri, May 5  no infection 4%  (49%) x May 14 x x x x
Sat, May 6  no infection 7%  (42%) x May 15 x x x x
Sun, May 7  no infection 4%  (39%) x May 16 x x x x
Mon, May 8  no infection 2%  (37%) x May 16 x x x x
Tue, May 9  no infection 3%  (35%) x May 16 x x x x
Wed, May 10  no infection 4%  (31%) x May 16 x x x x
Thu, May 11    5%  (26%) May 17 May 17 none none none none
Fri, May 12  5%  (21%) May 17 May 17 none none none none
Sat, May 13  3%  (18%) May 17 May 17 none none none none
Sun, May 14  4%  (14%) May 17 May 18 none none May 18 May 18
Mon, May 15  6%  (8%) May 17 May 18 none none May 18 May 18
Tue, May 16  8%  (0%) May 17 May 19 none none May 18 May 18
Wed, May 17  31% Late bloom only May 18 May 20 none none May 18 May 18
Late cultivar 100% PF
on Thu, May 18 
18%   Late bloom only May 19 May 23 May 22 none May 21 May 21
Fri, May 19  8% Late bloom only May 20 May 24 May 22 none May 21 May 21
Sat, May 20  Late bloom only May 21 May 25 May 22 none May 21 May 21
Sun, May 21  Late bloom only May 22 May 26 May 22 none May 22 May 22
Mon, May 22  Late bloom only May 23 May 27 May 23 none none none
Tue, May 23  Late bloom only May 28 May 28 none none none none
Wed, May 24  Late bloom only May 29 May 29 none none none none
Thu, May 25  no infection   Late bloom only x May 30 x x x x