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Models: Diseases

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Crop: Processing Tomato

Disease: Blackmold
Pathogen: Alternaria alternata

Note: Before using a model that was not field tested or validated for a specific location, the model should be tested for one or more seasons under local conditions to verify that it will work in this location. See "Model Validation" below.

Model 1 of 2

Model developer and citation

Modifications of TOM-CAST by Campbell Soup Company and UC researchers.

Pitblado, R. E. 1992. The development and implementation of TOM-CAST: A weather-timed fungicide spray program for field tomatoes. Ministry of Agriculture and Food, Ontario, Canada.

Madden L., Pennypacker, S. P., and McNab, A. A. 1978. FAST, a forecast system for Alternaria solani on tomato. Phytopathology 68:1354-1358.

Sensor location

Within canopy.

Input variables

Environmental: Leaf wetness duration, air temperature.

Calculated: Mean air temperature during the leaf wetness period.

Host: Variety, canopy height.

Model description

Disease severity values (DSV) are calculated as a function of hours of leaf wetness and average air temperature during leaf wetness. The DSV is based on the FAST early blight model of tomato. See Model 2 for a table of DSVs (Madden, et al. 1978). The accumulation of DSVs starts on July 1 or at first occurrence of fruit color and continues until 7-10 days before harvest (October). After treatment, the DSV accumulations reset to zero.

Action threshold

According to the model, initiate first treatment when 12 DSVs have accumulated for susceptible varieties and 18 DSVs have accumulated for resistant varieties. Subsequent treatments should occur each time 12 DSVs or 18 DSVs have accumulated for susceptible and resistant varieties, respectively.

Model validation

This model is being validated by Campbell Soup researchers, California Tomato Research Institute, and M. Cahn, G. Miyao, R. M. Davis, C. Pickel, and K. Brittan, of the University of California, in the Sacramento Valley.

Model implementation

This model is being used by Campbell Soup growers and other processing tomato growers in Northern California.

Future directions of model

University of California researchers are evaluating the inclusion of additional host parameters in this model, such as the amount of ripe or sunburned fruit, and/or descriptions of canopy density.

Related works

Bolkan, H. A., and Reinert, W. R. 1994. Developing and implementing IPM strategies to assist farmers: an industry approach. Plant Dis. 78:545-550.

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Model 2 of 2

Model developer and citation

Madden, L., Pennypacker, S. P., and McNab, A. A. 1978. FAST, a Forecast System for Alternaria solani on Tomato. Phytopathology 68:1354-1358.

Sensor location

Beside the tomato row.

Input variables

Environmental: Leaf wetness duration, air temperature.

Calculated: Mean air temperature during the leaf wetness period.

Host: Variety, canopy height.

Model description

A forecasting system for early blight on tomato was developed to identify periods when environmental conditions are favorable for early blight development and to provide a schedule for efficient fungicide applications. There are two empirical models: one is a dew model and the other is a rain model. Each is to be used under its respective weather conditions.

The dew model assigns a disease severity value (S) ranging from 0-4 based on the mean daily temperature and the hours of leaf wetness during that day, with 0 representing unfavorable conditions for disease development and 4 representing highly favorable conditions. The S values are accumulated since the beginning of the growing season into a variable called TS, and are accumulated for the past seven days into a variable called CS. Table 1 shows the temperatures and leaf wetting times required to derive the daily disease severity value.

Table 1: The Dew Model
Mean Temp(C) Mean Temp(F) Hours of Leaf Wetness Required to Produce Daily Disease Severity Value (S) of:
0 1 2 3 4
13-17 55.4-63.4 0-6 7-15 16-20 21+  
18-20 63.5-68.8 0-3 4-8 9-15 16-22 23+
21-25 68.9-77.8 0-2 3-5 6-12 13-20 21+
26-29 77.9-85 0-3 4-8 9-15 16-22 23+

The rain model works in the same way, but here the disease severity value (R) ranges from 0-3, and is based on temperature, hours of humidity above 90%, and total rainfall. Table 2 illustrates how the disease severity value is derived in this case. The R values are accumulated for the past five days into a variable called CR.

Table 2: The Rain Model
Temperature Average (C) Temperature Average (F) Hours RH>90 Total Rain Disease Severity Value (R)
<22 <71.6 <60 <2.5 0
>22 >71.6 <60 <2.5 0
<22 <71.6 >60 <2.5 1
<22 <71.6 <60 >2.5 1
<22 <71.6 >60 >2.5 1
>22 >71.6 >60 <2.5 2
>22 >71.6 <60 >2.5 2
>22 >71.6 >60 >2.5 3

Note that in Table 2, temperature is the average for the past 5 days, hours of relative humidity above 90% are accumulated over the past 5 days, and total rainfall is accumulated over the past 7 days.

Action threshold

The first early blight spray is recommended when TS reaches 35 and the plants are in the field for at least 5 weeks. Subsequent applications are made when CS or CR reach critical levels. These levels were still subject to further tests at the time the paper was published.

Model validation

The original validation was done in Pennsylvania. The model has since been adapted for use in timing tomato blackmold sprays in Canada and California, and has also been applied to other crops and diseases.

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