

Research and IPMModels: Diseases
Crop: GrapeDisease: Botrytis Bunch Rot

Model 1 of 2 
Broome, J. C., English, J. T. Marois, J. J., Latorre, B. A. and Aviles, J. C. 1995. Development of an Infection Model for Botrytis Bunch Rot of Grapes Based on Wetness Duration and Temperature. Phytopathology 85: 97102.
Within canopy.
Environmental: Hourly average temperature (in Celsius), leaf wetness duration (hours)
Host: Host maturity affects infection by this pathogen. In grapes, the flowers and postveraison berries are the most susceptible host stages, unripe berries and young shoots are less susceptible. This information is not included as an input into the model but should be taken into account when using this environmentally driven infection model.
Calculated variables: Average temperature during leaf wetness events.
This model identifies Botrytis cinerea infection periods on grape berries based on leaf wetness duration and the average temperature during the wetness events. The model was developed using mature detached grape berries in controlled humidity chambers that were subjected to 4, 8, 12, 16, or 20 hours of wetness at temperatures between 12 and 30 C. A multiple regression model best described (R^{2}=0.75) the logit of berry infection as a function of the interaction of wetness duration and temperature:
Infection Index = ln (Y/1Y) = 2.647866  0.374927W + 0.061601WT  0.001511WT^{2}
Where: W = leaf wetness duration in hours; T = temperature in Celsius; and ln (Y/1Y) = the logit of disease incidence where Y = the proportion of infected berries.
Additional model assumptions/implementation considerations:
The disease index is calculated whenever leaf wetness is detected.
The model predicts the following infection risks when the logit value is:
Infection Index Values  Risk Levels 

Infection Index < = 0  no risk of infection 
0 < Infection Index < 0.50  low risk of infection 
0.50 < = Infection Index < 1.00  moderate risk of infection 
1.00 > Infection Index  high risk of infection 
Fungicide applications should be based on how much risk one wants to accept. Typically, if the disease index value is 0.5 or greater implementors of the model have decided to apply a fungicide. This action threshold can be adjusted up or down depending on the known history of Botrytis bunch rot in a vineyard, the grape variety, and the degree of host susceptibility due to degree of fruit maturity. If more than 16 hours of wetness occur during a wetness event, regardless of the temperature, then consider the event a severe infection event.
For Botrytis bunch rot all tissue is susceptible, shoots, leaves, flowers, and berries but the degree of susceptibility varies with mature berries and grape flowers being the most susceptible, and unripe berries and shoots being much less susceptible.
Broome, J. C., English, J. T. Marois, J. J., Latorre, B. A. and Aviles, J. C. 1995. Development of an InfectionModel for Botrytis Bunch Rot of Grapes Based on Wetness Duration and Temperature. Phytopathology 85: 97102.
The model was programmed into an automated weather station (Envirocaster) and validated for two years on Chilean table grapes. Fungicide applications based on the model allowed growers to reduce their use of fungicides by approximately 50% with equivalent disease control.
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Model 2 of 2 
Nair, N. G. and Allen, R. N. 1993. Infection of Grape Flowers and Berries by Botrytis Cinerea as a Function of Time and Temperature. Mycological Research 97(8): 10121014.
Not described.
Environmental: Temperature (in Celsius) and leaf wetness duration (in hours).
Host: Grape flowers and mature berries.
A statistical model was developed to describe both flower and berry infection as a function of wetness duration and incubation temperature. The model was developed by placing grape flowers in incubation chambers and exposing them to temperatures of 5, 10, 15, 20, 25, and 30 degrees Celsius and 1, 2, 4, 6, 8, 10, 12, 18, and 24 hours of wetness. Grape bunches were incubated at the same temperatures as above, and subjected to up to 24 hours of wetness at 3 hour intervals.
The statistical model described the data well for both flowers and berries. For flowers, the optimal temperature for infection was 23.7 degrees Celsius, at which point flowers became infected after only 1.3 hours of exposure to wetness. For berries, the optimal temperature for infection was 20.8 degrees Celsius, at which point berries became infected after 13.9 hours of exposure to wetness.
Nonlinear least squares minimization was used to estimate the means of the model constants in the following equation:
I = I_{max}[1  exp( (Qt/K_{time})^{2 })]
Where: Q = exp[((TT_{opt})/K_{temp})^{2}]
For flowers:
For berries:
For both flowers and berries, infection developed over a wide range of temperatures. The results indicate flowers require fewer hours of wetness to become infected than grape berries.
Not yet determined.
None was presented in this article.