Fire blight prevention respray dates

Background Information for this page
Return to Apple list for Westhampton MA
Weather data for Westhampton MA.  Forecast values begin September 18, 2018
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 18
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: May 7 
no infection 8%  (92%) May 9 May 11 none none none none
McIntosh King Bloom:
Tue, May 8 
no infection 9%  (83%) May 10 May 13 none none none May 12
Wed, May 9  no infection 10%  (73%) May 11 May 14 none none none May 12
Thu, May 10  no infection 10%  (63%) May 12 May 15 none none none May 12
Fri, May 11  no infection 7%  (56%) May 13 May 16 none none none May 15
Sat, May 12  29% 3%  (53%) May 15 May 17 none none none May 15
Sun, May 13  36% 6%  (46%) May 16 May 17 none none none none
Mon, May 14  27% 10%  (36%) May 16 May 18 none none none none
Tue, May 15  20% 10%  (26%) May 17 May 20 none none none May 20
Wed, May 16  27% 9%  (18%) May 18 May 21 none none none May 20
Thu, May 17  29% 11%  (7%) May 19 May 22 none none none May 20
Fri, May 18  29% 7%  (0%) May 20 May 23 none none none May 20
Sat, May 19  30% Late bloom only May 21 May 23 none none none May 22
Sun, May 20  36%   Late bloom only May 21 May 24 none none none May 22
Mon, May 21  26% Late bloom only May 23 May 25 none none none none
Late cultivar 100% PF
on Tue, May 22 
18% Late bloom only May 23 May 25 none none none none
Wed, May 23  7% Late bloom only May 24 May 26 none none none none
Thu, May 24  Late bloom only May 25 May 27 none none May 27 May 27
Fri, May 25  Late bloom only May 26 May 29 none none May 27 May 27
Sat, May 26  Late bloom only May 27 May 30 none none May 27 May 27
Sun, May 27      Late bloom only May 28 May 30 none none none none
Mon, May 28  Late bloom only May 29 May 31 none none none none
Tue, May 29  Late bloom only May 30 June 1 none none June 1 June 1