By James Chatfield, Joseph Boggs, and Erik Draper
The environmental component of the disease triangle is crucial for plant diseases. Plant pathologists talk about infection periods for specific plant diseases and whether these periods occur depend on such things as the number of hours of leaf wetness and relative humidity. Of course, this in turn is influenced by temperature. All this plays into the overall weather, which can be difficult to predict over the short term, to say nothing of an entire growing season.
Temperature and moisture, for example, play a big role in development of fireblight disease. Bad years for fireblight on callery pear or crabapple usually relate to how warm and wet it is during bloom. The years where there are massive blossom infections—the greatest occurrence is during wet weather during extended periods over 16.7 C (62 F)—are those where fireblight is worse. So, it depends on whether these conditions occurred during the bloom of a particular callery pear or crabapple in a particular part of the province or region.
Read the full article: Managing Difficult Plant Diseases