Fire blight models background information

Model logic sources

Timothy J. Smith, Report on the Development and Use of Cougar Blight 98C - A Situation Specific Fire Blight Risk Assessment Model for Apple and Pear.  Washington State University.
http://www.ncw.wsu.edu/fbsmith.htm

Timothy J. Smith, A Risk Assessment Model For Fire Blight of Apple and Pear, Version 1998 Update.  Washington State University.

Timothy J. Smith, Cougar Blight 2002 Fire Blight Risk Assessment Model. http://www.ncw.wsu.edu/treefruit/fireblight/2000f.htm.  Washington State University.

Timothy J. Smith, Fire blight Degree Hour Values.  http://www.ncw.wsu.edu/images/curve.gif.  Washington State University.

Paul W. Steiner and Gary W. Lightner, MaryBlyt 4.1,  A Predictive Program For Forecasting Fire Blight Disease in Apples and Pears, University of Maryland at College Park.  1992

Personal communication with the late Paul Steiner and Gary W. Lightner about subsequent updates in MaryBlyt model logic and epidemiology of fire blight.  Personal communication with Timothy J. Smith on fire blight epidemiology.

Management

Dave Rosenberger, Fire Blight Rundown, Scaffolds Fruit Journal 9:15, June 26, 2000, Cornell Cooperative Extension
http://www.nysaes.cornell.edu/ent/scaffolds/2000/6.26_disease.html

Timothy J. Smith, Suggested tactics for fire blight management, Good Fruit Grower, March 15, 1999.

Timothy J. Smith, Cutting Fire Blight From Infected Apples and Pears, Washington State University Extension, 1998.  http://www.ncw.wsu.edu/treefruit/blightcut.htm

Paul W. Steiner, Managing Fire Blight in Apples, Illinois Horticultural Society Meeting, January 2000.  http://www.caf.wvu.edu/kearneysville/articles/FB-MANAGE00.html

Paul W. Steiner, The Biology and Epidemiology of Fire Blight, Illinois Horticultural Society Meeting, January 2000.   http://www.caf.wvu.edu/kearneysville/articles/FB-BIOLOGY00.html

Paul W. Steiner, A Philosophy for Effective Fire Blight Management, State Horticultural Association of Pennsylvania Annual Meeting, January 2000.   http://www.caf.wvu.edu/kearneysville/articles/PHILOSOPHY2000.html

Paul W. Steiner, Problems Managing Fire Blight in High Density Orchards on M-9 and M-26 Rootstocks, State Horticultural Societies of Virginia and West Virginia, Annual Meeting, January 1998.   http://www.caf.wvu.edu/kearneysville/articles/SteinerHort100.html

Paul W. Steiner, How Good Are Our Options With Copper, Bio-Controls, and Aliette for Fire Blight Control?, State Horticultural Societies of Virgina and West Virginia, Annual Meeting, January 1998.   http://www.caf.wvu.edu/kearneysville/articles/SteinerHort200.html

Comparing Cougarblight and MaryBlyt 
            Both models track heat units (degree hours above a base of 60F) on days leading up to a wetting event, using slightly different methods to do so.  Only days with open blossoms count towards the accumulation. 

             Both models require some type of wetting to initiate infection, and allow for heavy dew in the absence of rain as sufficient to cause such wetting.  Dew that only affects the orchard grass is not enough to cause infection.  As there is no independent measure of heavy dew, an observation of 3 or more hours of leaf wetness is used as a proxy to represent the possibility of heavy dew.  This is an imperfect measure, but it is the best we have.  MaryBlyt also allows for infection on the day after a day with more than 0.1” rain even if that day has no rain or heavy dew.

             For Cougarblight, I use hourly values to accumulate heat units according to a chart published by Dr. Smith.  This is more accurate than using the daily high and low temperature chart included in the Pest Guide, and in the cases here generated a lower estimate of heat units than the daily high-low chart gives for the same days.

             In Cougarblight, the number of accumulated heat units on the 3 days before a wetting event are added to those added on the day of wetting.  This total is then compared to thresholds defined according to the orchard and regional fire blight history during the past two seasons.

             MaryBlyt also accumulates for as many days as fall within 80 degree days base 40.  This usually turns out to be 4 days just like Cougarblight, but it does allow adjustment for longer or shorter persistence of individual blossoms under unusually cool or warm conditions.  MaryBlyt also requires that the average temperature on the day of infection be at least 60F.

        Comparisons of the two models by William Turechek and Deb Breth of Cornell University have shown that they are very similar in identifying possible fire blight infection periods.  The choice or model is much less important than using at least one of the two to keep a watch for possible infection conditions.  Given that inoculum levels are low in Maine, I prefer Cougarblight because it gives more information on interpreting conditions for low inoculum situations.