Fireblight infection conditions - Cougarblight model

Background Information for this page
Return to radar list for Middletown RI
Weather data for Middletown RI.  Forecast values begin May 20, 2013
     This table shows estimates of RELATIVE daily fireblight 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 of open flowers, and cultivar and rootstock susceptibility.  Relative infection risk may be overstated for first few days of bloom because fire blight bacteria may not have been distributed to open flowers.   
      Gray shading indicates dates when most trees will have lost open blossoms, and are therefore no longer susceptible to blossom infection.  These dates included for later blooming cultivars and for late-blooming young trees.  Absolute risk is much lower on these dates than during full bloom, but apple trees with open blossoms on these dates are susceptible to the risk rating shown.  
      Fireblight infection can occur without rain if there is "heavy" dew.  But heavy dew is not defined in weather reports.  As a rough guess, if there is no rain on a day, but leaves are expected to be wet for at least 3 hours, then infection risk is reported with "if dew" attached.  Infection potential may be overstated on days when the "if dew" tag is attached.
     Fire blight risk estimate varies by block history:
   I  = No active fire blight within 1 mile of the orchard this year or last year.  Requires 500 – 800 heat units for HIGH rating, 801 – 1000 for EXTREME!, and 1001+ for EXCEPTIONAL!
  
II = Fire blight was present within 1 mile of the orchard last year, but not currently active in the area this year.
Requires 200 – 350 heat units for HIGH rating, 351 – 500 for EXTREME!, and 501+ for EXCEPTIONAL!

  
III = Active fire blight cankers within 1 mile of the orchard this year. 
Requires 100 – 200 heat units for HIGH rating, 200 – 300 for EXTREME!, and 301+ for EXCEPTIONAL!
 If blossom infection occurred May 22, then blossom blight would be noticeable by June 5, and shoot blight by June 14.
Range of potential open blossom dates
for McIntosh and similar cultivars
Cougarblight Heat Units,
Inches Rain, & 
Leaf Wet Hours
I - No FB within
one mile last year
or this year
II - FB within one mile last year, but not active within one mile this year III - FB active within one mile of orchard this year.
McIntosh King Bloom
 Tue, May 7 
11 HU,  0.0'',  16 hrs Low Low Caution
Wed, May 8  25 HU,  0.21'',  18 hrs Low Low Caution
Thu, May 9  34 HU,  0.43'',  24 hrs Low Low Caution
Fri, May 10  62 HU,  0.03'',  11 hrs Low Low Caution
Sat, May 11  59 HU,  0.81'',  23 hrs Low Low Caution
Sun, May 12  53 HU,  0.01'',  14 hrs Low Low Caution
Mon, May 13  46 HU,  0.0'',  0 hrs Low Low Low
Tue, May 14  21 HU,  0.0'',  0 hrs Low Low Low
Wed, May 15  18 HU,  0.04'',  9 hrs Low Low Caution
Thu, May 16  36 HU,  0.0'',  9 hrs Low Low Caution
Fri, May 17  43 HU,  0.0'',  0 hrs Low Low Low
Sat, May 18  51 HU,  0.0'',  0 hrs Low Low Low
Sun, May 19  56 HU,  0.47'',  8 hrs Low Low Caution
Mon, May 20  67 HU,  0.04'',  24 hrs Low Low Caution
Tue, May 21  87 HU,  0.17'',  24 hrs Low Low Caution
Wed, May 22  133 HU,  0.10'',  16 hrs Low Caution HIGH
Thu, May 23  180 HU,  0.48'',  20 hrs Caution Caution HIGH
Fri, May 24  167 HU,  0.24'',  24 hrs Caution Caution HIGH
Sat, May 25  152 HU,  0.0'',  7 hrs Caution (if dew) Caution (if dew) HIGH (if dew)
Sun, May 26  111 HU,  0.0'',  0 hrs Low Low Low
Mon, May 27  65 HU,  0.0'',  0 hrs Low Low Low