Fire Blight - Cougarblight Risk Assessment Model

For Pears!

Try out the - Cougarblight forecasting system!

Use the Cougarblight Risk Assessment Model by yourself!

Cougarblight is a risk assessment model for determining the risk of fire blight infection on flower blossoms. The model was developed at Washington State University in the 1980s and is the standard for fire blight risk assessment in Oregon and Washington. It is included here as it may be of use in the Northeast in prediction of fire blight outbreaks after a blossom wetting event. This model should be used from first bloom until only a few blossoms remain. The model estimates the level of risk for fire blight infection based on degree days and history of fire blight in or around your orchard the previous growing season.

Season 2008 - Running!

Click on the name of the location below to obtain an risk prediction for a given region. Below the table and Introduction are the guidelines for using the model. Remember, the models won't start running until bloom is reached. Dead stations are in red, while green stations have reached the biofix and are running. If the pears in your region have reached bloom, please contact your regional Cornell Cooperative Extension specialist or contact me to get your region up and running.

Cougarblight Risk Predictions - 2008
Guilderland,
Albany Co.		 Lockport,
Niagara Co.		 Watkins Glen,
Schuyler Co.
Hudson,
Columbia Co.		 Peru,
Clinton Co.		  

Guidelines for using the model and interpreting the risk prediction results

Step 1 - It is first necessary to determine the 'Blight History' of your orchard.

 

'Blight History'

 

Description of Fire Blight History
1
 No fire blight in the area for the past two years.
2
 Fire blight present in the region, but not in, or near, your orchard last year.
3.
 Fire blight in, or near, your orchard last year.
4
 Fire blight strikes or cankers presently in, or near, your orchard.

 

Step 2 - When your orchard enters bloom, look up the '4-day degree-hour sum' using the graphs for your region. Click on your region located in the table at the top of the page. A pop-up window will emerge with various graphs specific to your region.

Step 3 - Look at the blue bar graph to determine your 4-day degree hour sum. Cross reference this number with your 'Blight History' (from Step 1.)in the table below. This is also represented graphically (red bar graphs) for each region below the degree hour summary (blue bar graph). Your risk is rated as either 'low', 'moderate' 'high', or 'extreme'.

 

 

4-day Degree-hour Sum
'Blight History'
Low (1)
Moderate (2)
High (3)
Extreme (4)
1
0-400
400-500
500-800
800+
2
0-350
350-400
400-650
650+
3
0-150
150-300
300-500
500+
4
0-100
100-200
200-350
350+

 

Step 4 - Look at the weather data graph at the top of pop-up window for your region. Compare rainfall events with the risk obtained from step three and decide whether to take action based on the following guidelines:

A. If there was rainfall at the time in question (i.e. rain fall in the weather graph), blossom wetting has occured and usually indicates a possible infection event. Check you Risk Prediction Level

B. If the "Risk Prediction level" was near or in the range of "High (3)" spray controls are often required

C. If the "Risk Prediction level" was near or in the range of "High (4)" Severe outbreaks may occur.

 

You can access Cougarblight directly to assess your risk of fire blight and see the original notations made by Timothy J. Smith of WSU Cooperative Extension or use the guide below to estimate the risk of fire blight in your orchard. The original site has a very informative discussion of risk factors and considerations to keep in mind when using the model.

  1. Determine the fire blight history of your orchard and its environs for the last two seasons. Blight history is assigned as one of the following:
      • No fire blight in the area for the past two years
      • Fire blight present in the region, but not in or near your orchard last year.
      • Fire blight in or near your orchard last year
      • Fire blight strikes or cankers presently in or near your orchard
  2. Use the high and low temperature for the last 4 days prior to blossom wetting (temperature forecasts can also be used to predict control decisions) to calculate daily degree hours using the chart below. For example, if the high and low temperatures for the last three days have been 74/44F, 76/45F, 78/50F, and today is predicted to be 73/44F, your degree hours would be 100 + 130 + 189 + 87 = 506
    Daytime High Temperature Degree Hours per night if low is 49.9F or less Degree Hours per night if low is 50F or higher Daytime High Temperature Degree Hours per night if low is 49.9F or less Degree Hours per night if low is 50F or higher
    60
    0
    0
    83
    243
    280
    62
    2
    5
    84
    257
    292
    63
    5
    12
    85
    266
    302
    64
    10
    22
    86
    274
    310
    65
    14
    29
    87
    280
    315
    66
    20
    35
    88
    285
    320
    67
    26
    42
    89
    288
    325
    68
    33
    50
    90
    290
    330
    69
    42
    60
    92
    287
    335
    70
    52
    70
    93
    284
    333
    71
    62
    80
    94
    280
    330
    72
    47
    92
    95
    274
    325
    73
    87
    105
    96
    267
    317
    74
    100
    120
    97
    260
    309
    75
    115
    134
    98
    254
    302
    76
    130
    151
    99
    246
    293
    77
    146
    169
    100
    238
    285
    78
    162
    189
    101
    230
    275
    79
    178
    209
    102
    222
    268
    80
    195
    230
    103
    216
    259
    81
    212
    250
    104
    208
    250
    82
    228
    265
    105
    200
    240
  3. Cross-reference your degree hour sum with your blight history to determine your Cougarblight risk prediction.
    Blight history
    4-day degree hour sum
    low risk marginal risk high risk extreme risk
    None in your area during the past 2 seasons 0-400 400-500 500-800 800+
    Blight in the region but not near your orchard in the last year. 0-350 350-400 400-650 650+
    Blight in or neighboring your orchard last year 0-150 150-300 300-500 500+
    Active blight strikes or cankers in your orchard or a neighboring orchard 0-100 100-200 200-350 350+
  4. Determine what, if any action is required. Generally a risk prediction level near or above high requires control measures.

*Considerations: