Welcome to TOMCAST

TOMCAST (TOMato disease foreCASTing) is a computer model model which uses local weather conditions to predict fungal disease development, on tomatoes, specifically Early Blight, Septoria Leaf Spot and Anthracnose. TOMCAST does not predict bacterial diseases such as Speck, Spot, or Canker, not does it predict viral outbreaks

Data loggers, such as Campbell Scientific CR10's, (Button, left) are placed near tomato fields where they record hourly leaf wetness and temperature. Every 24 hours these data are analyzed and converted to Disease Severity Values (DSV), units of disease development. DSV are added from day to day until they exceed a pre-determined threshold which triggers a recommendation to apply a fungicide, preventing infection of plant foliage and fruit. The network becomes operational May 15th, with all stations reporting DSV through September 30th.

TOMCAST is derived from the original F.A.S.T. (Forecasting Alternaria solani on Tomatoes) model developed by Drs. Madden, Pennypacker, and MacNab at Pennsylvania State University. The F.A.S.T. model was further modified by Dr. Pitblado at the Ridgetown College in Ontario into what we now recognize as the TOMCAST model used by Ohio State University throughout Ohio, Indiana, and Michigan. Extension.

If you would like more details on using TOMCAST in your operation, refer to the 1998 Ohio Vegetable Production Guide, The TOMCAST section within the Tomato Chapter.

Why DSV are important

The TOMCAST model generates Disease Severity Values (DSV’s) as units of disease development for pathogens such as Early Blight, Septoria Leaf Blight, and Anthracnose. DSV are a numerical representation of the rate at which disease pressure is accumulating on tomato plant tissue. The DSV is determined by two factors, leaf wetness and temperature during the leaf wet hours. As the number of leaf wet hours and temperature increases, DSV accumulate at a faster rate, i.e., increased disease pressure. Conversely, when there are fewer leaf we hours and the temperature is lower, DSV accumulate slowly if at all, i.e., decreased disease pressure. The chart below shows the interaction between those two factors.

When the total number of accumulated DSV exceeds a pre-determined limit, the spray threshold, a fungicide spray is recommended to protect the foliage and fruit from disease development. The spray threshold can range between 15-20 DSV. The exact DSV a grower should use is usually supplied by the processor and depends on the fruit quality and end use of the tomatoes. By following a 15 DSV spray threshold, a more conservative use of the TOMCAST system, a grower will apply fungicides more frequently than a grower who uses a 20 DSV spray threshold. The tradeoff is in the number of sprays applied during the season and the potential for differences in fruit quality. A 15 DSV spray threshold can be roughly translated into a 7-10 day spray program, while growers on a 20 DSV spray threshold program treat on average every 10-14 days. Some suggested fungicide programs to be used with TOMCAST are mentioned in this excerpt.

For suggested fungicide programs to be used with Tomcast, click the spray program button, left.

Who can use TOMCAST?

Any tomato grower within a 10-15 mile radius of a reporting station can take advantage of TOMCAST's information to schedule fungicide applications. There is no charge for this service. If this is your first time experimenting / using TOMCAST, be sure to read the next section for a few hints and ideas to consider while using the network. Current TOMCAST locations are shown below in a table.

Station/City	State	Station/City	State	Station/City	State
Fremont	OH	LaCrosse	IN	Petersburg	MI
McGuffy	OH	Galveston	IN	Constantine	MI
Pandora	OH	Hobbs	IN
Napoleon	OH	Union City	IN
*Hillsboro	OH
*Racine	OH
*Huntsburg	OH
* Fresh Market sites

First Time Users of TOMCAST

If this is your first exposure to TOMCAST, keep in mind these important ideas.

1. It is recommended that only part of a growers acreage be put into the program to see how it fits with existing quality standards and operational style.

2. Use TOMCAST as a guide to help schedule (time) fungicide applications, realizing in some seasons (warm and wet) growers may actually apply more product than a calendar spray program. Conversely, during cooler and drier seasons, growers will still enjoy the benefits of proper fungicide timing along with the possibility of fewer sprays.

3. IN RELATION OF A GROWERS FIELD TO THE NEAREST TOMCAST STATION.
The further a tomato field is from a reporting site increases the likelihood of distortion in the true DSV experienced by the growers field. The reported value may be close to the actual DSV at the field location. This should be taken into consideration when application of fungicides is a few days away.

By listening to the DSV reports of nearby stations it may be possible to triangulate the DSV accumulation to the field of concern. This is a fair way to roughly estimate DSV accumulation in more remote locations. Topographic features such as rivers, lakes, mountains, and valleys may compound any differences.

First Field Spray Using TOMCAST

The 1998 Ohio Vegetable Production Guide offers some suggestions as to when the first fungicide application on new field transplants should be made. Grower experience with early season plants may dictate other approaches, use the one that best fits your production needs.

In general, tomato transplants that enter the field on or before May 20 should have the first fungicide applied when DSV for the nearest station exceeds 25 or when a fail safe date of June 15 arrives. The fail safe date is used to protect plants that have not been treated since being transplanted; its purpose is to eliminate initial disease inoculum.

Tomatoes transplanted after May 20 are treated when they exceed the chosen spray threshold (15-20 DSV).

After the first spray, all subsequent applications are based on the spray thresholds only. Don't forget to subtract DSV that have accumulated prior to the transplant date. No sense in subjecting the transplants to phantom DSV! A modified TOMCAST worksheet has been designed to address the transplanting / first spray interaction, as well as the remaining fungicide sprays.

Accessing TOMCAST DSV Reports: The DSV Hotline 800-228-2905

There are many ways to access the DSV information generated by TOMCAST. We have set up a toll free, 24 hour message recorder which reports the most current DSV information long with any additional pertinent information such as insect activity reports. Message duration is usually 1-3 minutes.

Alternate means for accessing TOMCAST DSV reports include the Disease Forecast button on this homepage, the current issue of VegNet newsletter, and Farmdayta and DTN broadcast systems under both the field crop and vegetable packages.

BLITECAST

BLITECAST is a Late Blight disease forecasting model similar to TOMCAST, using weather data to generate daily Severity Values (SV). If the cumulative SV exceed a threshold value of 18, a fungicide application is recommended unless an application has been made in the previous 7 days. The environmental conditions conducive to Late Blight development are generally cool and wet. Late Blight was detected in Ohio and other nearby states last year.

Late Blight Scouting Guidelines
Tomatoes grown under weather conditions conducive to Late Blight development or near potatoes that have been infected with Late Blight require periodic scouting. It is crucial to scout for this disease in areas that are difficult to reach with a sprayer or remain wetter than other parts of the field. If a fungicide has been applied within the past 7-14 days (i.e., sprays called for by TOMCAST), the threat of Late Blight is substantially reduced. If a fungicide has not been applied to a tomato field in an area identified as conducive to late blight development within the previous 7-14 days, a prophylactic spray may be justified. If Late Blight has been identified in a field, immediate use of a fungicide is recommended until harvest.

A Tomato Late Blight Management Guide is available from OARDC Plant Pathology if more information regarding the subject is needed. Ask for PP Dept Series # 99, Potato and Tomato Late Blight, 1995 Update and Recommendations.

TOMCAST Supporters

Support for this project is provided by research funds secured through Mid America Food Processor Association, Ohio State University Extension IPM Mini-Grants, Ohio Vegetable and Small Fruit Research and Development Program, Fremont Pickle and Tomato Growers Association, USDA Competitive Grants, and other miscellaneous grant support generated by faculty at the Ohio State University Extension.

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