Fireblightinfectionconditions-Cougarblightmodel

Background Information for this page
Return to Apple list for Easthampton MA
Weather data for Easthampton MA. Forecast values begin May 25, 2018
This table shows estimates of RELATIVE daily fire blight blossom infection risk based on weather conditions. Rating criteria are from the CougarBlight 2010 model developed in Washington and Oregon by Dr. Timothy J. Smith.
ABSOLUTE risk depends on the amount of fire blight bacteria in the area, the number and age of open flowers, tree age (1-5 years old most vulnerable), cultivar and rootstock susceptibility. Ratings are for flowers that have NOT received an application of streptomycin or other fire blight suppression material. You can use the daily heat unit values between application date and a subsequent wetting event to estimate heat unit accumulaiton for flowers that received antibiotic treatment. Relative infection risk may be overstated for first few days of bloom because fire blight bacteria may not have been distributed to open flowers. Individual cutltivars may start or finish bloom a day or two earlier or later than the range of open blossom dates shown. Gray shading indicates dates when most trees will have lost open blossoms, but late blooming cultivars,"straggler" or secondary bloom (e.g. Cortland and Golden Delicious), or young trees may still have open flowers and be susceptible to blossom blight. Infection of a few late blooms can provide a foothold for fire blight to colonize an orchard.
Fireblight infection can occur without rain if there is wetting caused by dew. If there are enough heat units for infection but no rain, if leaves are expected to be wet for 2 or more hours, then infection risk is reported with a "dew risk" label. Infection potential on"dew risk" days is not well understood. Infection potential may increase with high relative humidty prior to and during infection events, and be reduced by an extended period of low relative humidity.
Fire blight blossom infection risk varies with block history. If you do not know orchard history, use category II as default assumption.
I = No active fire blight within 1 mile of the orchard in last two years. Requires 500 799 heat units for HIGH rating, 800 999 for EXTREME!, and 1000+ for EXCEPTIONAL!
II = Fire blight was present within 1 mile of the orchard within last 2 years, but not currently active in the area this year.
Requires 200 349 heat units for HIGH rating, 350 499 for EXTREME!, and 500+ for EXCEPTIONAL!

III = Active fire blight cankers within 1 mile of the orchard this year.
Requires 100 199 heat units for HIGH rating, 200 299 for EXTREME!, and 300+ for EXCEPTIONAL!
If blossom infection occurred May 12, then blossom blight would be noticeable by May 26, and shoot blight by June 4.
Open blossom dates for common apple cultivars.
"Date" is from 8am to 8am the next day, not midnight to midnight.
Cumulative Heat Units (single day units)
Inches Rain,
&
Leaf Wet Hours
8am to 8am next day
I - No active FB within one mile of the orchard in last two years II - FB active within one mile of orchard in last two years, but not this year III - Fire blight currently active within one mile of orchard. Date blossom blight (and shoot blight) symptoms would be obvious if infection occurred
possible early cultivar
King Bloom: May 7
22 HU (22)
0.0'', 7 hrs
Low
(lack of heat)
Low
(lack of heat)
Unlikely
(lack of heat)
 
McIntosh King Bloom:
Tue, May 8
69 HU (47)
0.0'', 2 hrs
Low
(lack of heat)
Low
(lack of heat)
Caution
(if wetting)
 
Wed, May 9 184 HU (115)
0.0'', 0 hrs
Caution
(if wetting)
Caution
(If wetting)
High
(if wetting)
May 25, (June 3)
Thu, May 10 207 HU (23)
0.0'', 0 hrs
Caution
(if wetting)
High
(if wetting)
Extreme!
(if wetting)
May 26, (June 4)
Fri, May 11 198 HU (12)
0.0'', 0 hrs
Caution
(if wetting)
Caution
(If wetting)
High
(if wetting)
May 26, (June 4)
Sat, May 12 151 HU (0)
0.23'', 22 hrs
Caution Caution HIGH May 26, (June 4)
Sun, May 13 40 HU (5)
0.0'', 4 hrs
Low
(lack of heat)
Low
(lack of heat)
Unlikely
(lack of heat)
 
Mon, May 14 62 HU (45)
0.0'', 4 hrs
Low
(lack of heat)
Low
(lack of heat)
Caution
(if wetting)
 
Tue, May 15 155 HU (105)
0.98'', 24 hrs
Caution Caution HIGH May 28, (June 6)
Wed, May 16 168 HU (13)
0.0'', 9 hrs
Caution
(dew risk)
Caution
(dew risk)
HIGH
(Dew risk)
May 28, (June 6)
McIntosh 95% Petal Fall
on Thu, May 17
227 HU (64)
0.0'', 5 hrs
Caution
(dew risk)
HIGH
(Dew risk)
EXTREME!
(Dew Risk)
May 29, (June 7)
McIntosh 100% Petal Fall
on Fri, May 18
193 HU (11)
0.0'', 0 hrs
Caution
(if wetting)
Caution
(If wetting)
High
(if wetting)
May 29, (June 8)
Sat, May 19 95 HU (6)
0.53'', 23 hrs
Low
(lack of heat)
Low
(lack of heat)
Caution  
Sun, May 20 153 HU (71)
0.08'', 24 hrs
Caution Caution HIGH May 30, (June 8)
Mon, May 21 182 HU (93)
0.0'', 1 hrs
Caution
(dew risk)
Caution
(dew risk)
HIGH
(Dew risk)
May 31, (June 9)
Late Cultivar Petal Fall
on Tue, May 22
181 HU (10)
0.09'', 20 hrs
Caution Caution HIGH May 31, (June 10)
Wed, May 23 401 HU (226)
0.0'', 3 hrs
Caution
(dew risk)
EXTREME!
(Dew Risk)
EXCEPTIONAL!
(DEW RISK)
June 1, (June 11)
Thu, May 24 459 HU (130)
0.0'', 0 hrs
Caution
(if wetting)
Extreme!
(if wetting)
Exceptional!
(if wetting)
June 2, (June 11)
Thu, May 24 459 HU (130)
0.0'', 0 hrs
Caution
(if wetting)
Extreme!
(if wetting)
Exceptional!
(if wetting)
June 2, (June 11)
Sat, May 26 1136 HU (368)
0.21'', 13 hrs
EXCEPTIONAL! EXCEPTIONAL! EXCEPTIONAL! June 6, (June 14)
Sun, May 27 917 HU (8)
0.50'', 24 hrs
EXTREME! EXCEPTIONAL! EXCEPTIONAL! June 6, (June 15)
Mon, May 28 825 HU (38)
0.04'', 20 hrs
EXTREME! EXCEPTIONAL! EXCEPTIONAL! June 7, (June 15)
Tue, May 29 660 HU (246)
0.0'', 1 hrs
HIGH
(Dew risk)
EXCEPTIONAL!
(DEW RISK)
EXCEPTIONAL!
(DEW RISK)
June 8, (June 16)
Wed, May 30 402 HU (110)
0.0'', 0 hrs
Caution
(if wetting)
Extreme!
(if wetting)
Exceptional!
(if wetting)
June 9, (June 17)
Thu, May 31 507 HU (113)
0.0'', 0 hrs
High
(if wetting)
Exceptional!
(if wetting)
Exceptional!
(if wetting)
June 10, (June 18)
Fri, June 1 592 HU (123)
0.0'', 0 hrs
High
(if wetting)
Exceptional!
(if wetting)
Exceptional!
(if wetting)
June 11, (June 19)