Developed by Dr. R.E. Pitblado, formerly of Ridgetown Campus, University of Guelph, TOMcast is disease-warning model which establishes a timed fungicide spraying program for Early Blight, Septoria Leaf Spot and Anthracnose on processing tomatoes. TOMcast is based upon weather data, specifically leaf wetness and temperature. Disease control is obtained from the accumulation of daily Disease Severity Values (DSV’s) which results in a recommendation for fungicide applications.

The TOMcast program publishes 7 days week. TOMcast can also be delivered as customer specific DSV values according to each subscriber’s unique field locations. At season's end, TOMcast clients can expect a summarized wrap up report loaded with weather information from the concluding season.

How It Works

Dr. Ron Pitblado

What Drives TOMcast? DSV = Leaf Wetness + Temperature

A fungus needs free moisture to germinate and infect tomato plant tissue. If the leaf surface is dry the fungal spore, like a weed seed, just sits there...and waits. The rate or speed of infection is determined by temperature. The cooler the temperature the slower the process whereas the warmer the temperature the faster infection takes place, disease occurs.

Simple! We have an environmental factor that starts the disease and another environmental factor that speeds up or slows down the progress of the disease. For sure there are other conditions that influence tomato diseases such as the genetics or varietal characteristics of the tomato plant itself, some are more susceptible others are more resistant with a third component being the presence or absence of the fungus itself. TOMcast assumes the pathogen, whether it be Septoria Leaf Spot, Early Blight or Anthracnose is always there. We have been growing tomatoes in this area for years and fungi can overwinter and survive in crop debris.

Why Disease in My Field?

You may remember when it rains but may not appreciate the length of dew periods. Both contribute to leaf wetness. It does NOT have to rain for tomato plant diseases to get started. This is why it is so important to have these map images burned in your mind. No one of us can, without the aid of weather recording instruments, observe or certainly remember all the permutations that go into the onset of tomato diseases. That of course is why TOMcast was developed in the first place.

TOMcast was not designed to save you money...But it will!

Are there differences between diseases?

Yes. We can categorize our tomato diseases into two groups. The fungal diseases that TOMcast was developed for and the bacterial diseases Bacterial Spot, Speck and Canker continue to give us control problems. In the common vernacular of plant pathologist we describe the two classes of diseases as follows:

• Simple Interest Diseases - diseases that are slow to initiate and that if the weather turns cool and dry, the disease progress is slowed or even stopped. Examples, Septoria Leaf Spot, Early Blight and Anthracnose.
• Compound Interest Diseases - diseases that start very quickly and accumulate just like compounding interest at a bank. Once the disease is started you must attack the disease control practices vigorously. Examples: Bacterial Spot, Speck and Canker along with the fungal disease Late Blight.

It’s the compound interest diseases that we have so many problems with - the bacterial diseases in tomatoes. There has been a tremendous effort of late to vigorously attack the initiation of the disease through seed treatments and moisture control at the greenhouse seedling stage. It is my hope that these early disease control strategies are enough to slow the disease before it gets to the field so that field production strategies need not concern themselves with any early - prior to July 11 bacterial control sprays. Certainly after July 11 all growers need only to follow TOMcast.

The Power of WIN's site specific capabilities

WIN’s site specific mapping capabilities have significantly improved the accuracy of defining regions of disease potential. When TOMcast was first developed this option did not even exist. You will remember we created 4 spray zones in Essex and 5 spray zones in Kent. We all knew of course, that the incidence of disease never did follow our strict lines of demarcation between, let’s say, spray zone A and zone B. This necessitated a predictive program that was very conservative, i.e. spray every 20 DSVs. Now with our ability to adapt and implement new technology we can more accurately map out the regions of higher or lower DSV with the result that growers who use TOMcast can comfortably without risk extend their spray intervals to 25 or even 30 for the more resistant tomato varieties. With the newer fungicides being developed and soon to be registered I can see the number 30 DSVs being used widely.