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How to Manage Pests
Interactive Tools and Models: About the Spray Forecast for Tomato Powdery Mildew
TomatoPM is a computer representation of the spray
forecast model for tomato powdery mildew, developed by R. Guzman-Plazola,
R. M. Davis, and J. J. Marois at the University of California, Davis,
and sponsored by the California Tomato Research Institute and California
Tomato Board. This Web version replaces the Excel version published
earlier.
References
- Guzman-Plazola, R. A. 1997. Development of a spray forecast model
for tomato powdery mildew (Leveillula taurica (Lev) Arn).
Ph.D. Thesis. University of California, Davis.
- Davis, R. M. and J .J. Marois. Development of a spray forecast
model for powdery mildew of tomato. California Tomato Research Institute
1995 Final Report. pp. 52-59. In conjunction with R. Guzman-Plazola.
The model is based on results from experiments under controlled conditions
(growth chamber) and field monitoring of disease and weather data.
A linear discriminant function was generated to classify daily environmental
conditions of tomato canopies according to their conduciveness for
disease. Cross-validation of the discriminant function and tests with
independent data sets yielded percentages of correct classification
of 74-96% and 87%, respectively.
The model was tested during two consecutive years (1995 and 1996)
in ten tomato fields (fresh market and processing) in the northern
San Joaquin and southern Sacramento valleys of California. After following
the recommendations of the model, it was possible to save 2 to 5 fungicide
sprays with no significant impact on fruit yield and quality. Disease
levels at harvest time in plots managed according to the model have
been equal to or only slightly higher than that of plots where fungicide
applications were made every 14 days.
In generating a spray forecast, the model
- Analyzes hourly weather data.
- Classifies the conditions for each day in terms of conduciveness for disease.
- Evaluates the daily conditions over the most recent period (usually 6 days) to assess the risk of low, moderate, or severe disease.
- Recommends management action based on the conditions over the period.
This model assumes the following:
- Unlimited inoculum of Leveillula taurica is present in the field.
- The tomato cultivar in use is susceptible to Leveillula taurica.
- There was no disease risk before the first day of data to be evaluated by TomatoPM.
- Fungicide sprays can reduce infection in progress and provide effective protection against the disease for 10 days.
- Location of sensors in the field and sensor measurements are representative of tomato canopy microclimate in the rest of the field.
While the results are very promising, remember that
- If using the model in new areas, it should be tested for one or
more seasons under local conditions to verify that it will work
in your location. Monitor fields closely for disease while testing
the model.
- Sensors must be calibrated to give accurate results.
- The model uses microclimate data from tomato canopies, so proper
placement of the sensors is very important for correct classification
of daily conditions.
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