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How to Manage Pests

Interactive Tools and Models: About the Spray Forecast for Tomato Powdery Mildew

Collecting weather data and preparing the data file

The California Tomato Weather Network (map), starting in the 2002 field season, collects weather data compatible with TomatoPM. However, you may not be near a station or may want the added information you get from monitoring the microclimate of your own field. The paragraphs that follow give you the requirements for monitoring the data yourself and supplying the file for use by TomatoPM.

Required sensors. One temperature (T), one relative humidity (RH), and one leaf wetness (LW) sensor are required. If two or more sets of sensors are used, hourly values for each sensor type should be averaged before using TomatoPM. The averages should then be entered into the data file, in the column for each sensor.

Placement of the sensors. Proper placement and calibration are critical for reproducing the research results. Starting in 2002, the stations in the California Tomato Network are set up to support TomatoPM.

T and RH. The sensors for T and RH should be placed together (they are usually parts of a single probe) and protected by a shield to avoid direct exposure to the sun and water, but the shield must allow good air flow around the sensor.

Since the forecast model uses microclimatic data at the canopy level, T and RH sensors must be placed inside the foliage and toward the top of the plants. Location of the sensors must be checked regularly, at least once a week, particularly during the fast growth stages of the tomato crop and after periods of high wind speeds.

LW. Leaf wetness sensors must be placed on the top of the canopy and relocated periodically according to the dynamics of plant growth.

Output variables. The weather station's datalogger should make several measurements from each sensor during an hour, to be averaged over the hour. Measurements reported more often than each hour must be summarized into hourly values for input into the model. See Table 1 for a list of required variables and their units.

Table 1. The data values required by the model and their default units.
Variable Units/Expected Values Data
Spreadsheet
Column
Date (month/day/year) Format: mm/dd/yyyy A
Hour of the day 0-2300, or 100-2400 B
Maximum of T for each hour Celsius C
Minimum T for each hour Celsius D
Average T for each hour Celsius E
Maximum RH for each hour Percent F
Minimum RH for each hour Percent G
Average of RH for each hour Percent H
Leaf wetness Scale 1-60 I

TomatoPM expects to find the uploaded-data in a tab-delimited text file. This file may be prepared initially as a spreadsheet, then saved as a tab-delimited text file. You may download a sample data file "weather2002.txt" to see how one should look.

The spreadsheet may indicate special data types and units, or contain comments. Use as many of the first rows as you need for these items, following these rules:

  • Begin all rows in column A.
  • Insert "*" (asterisk) as the first character for all comments.
  • If the spreadsheet dates are Julian days rather than standard dates in the mm/DD/yyyy format, indicate Julian day by inserting *JULIAN in the first cell of a row.
  • Indicate that the spreadsheet temperatures are in Fahrenheit instead of Celsius by inserting *FAHRENHEIT in the first cell of a row.

The spreadsheet should have data in the columns specified in Table 1, above. All hours must have a value. If you have missing data, fill in from hours on a similar day, use data from a similar station, or in some other way fill in the gaps. If you cannot fill the gaps, you will need to start a new file and enter a starting date that falls after the gap as the beginning date.

Note: You may download a sample data file "weather2002.txt" as an example of the required format.

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.

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