Model Blossom Blight for Pears

Fb1 Fb4 1 Fb2
  1. Flower must be open with stigmas and petals intact, stigmas have to be exposed for colonization, flowers in petal fall are resistant;
  2. Accumulation of at least 110 °C hours > 18.3°C within the last 66 °C days > 4.4 °C defines the epiphytic infection potential for the oldest open and hence most colonized flower in the orchard
  3. A wetting event occurring as dew or 0.2 mm of rain or 2.5 mm of rain the previos day allows movement of bacteria from colonized stigmas to the nectarthodes
  4. An average daily temperature of >= 15.6 °C: This may influence the rate at which the bacteria migrate into the nectarthodes as well as the multiplication of bacteria needed to establish infections.

When all four of these minimum requirements are met in the sequence shown, infections occur and the first early symptoms of blossom blight can be expected to appear with the accumulation of an additional 57 °C days > 12.7 °C. This can be 5 to 30 days after infection. When the orchard conditions are less than these minimum requirements, few or no symptoms occur and no significant epidemic develops. (STEINER P.W. 1996)