Ohio

Disease Enhancing the TOM-CAST Monitoring System via the Addition of Late Blight Disease Prediction

Principal Investigators:

 Jim Jasinski, Southwest IPM/ TOMCAST Coordinator
Bob Precheur, Dept. of Horticulture and Crop Science
Mac Riedel, Dept. of Plant Pathology
Mark Bennett, Dept. of Horticulture and Crop Science
Celeste Welty, Dept. of Entomology

Abstract:

 TOMCAST is a disease forecasting program used in thirteen processing and fresh market tomato field sites throughout southern Michigan, Indiana, and Ohio. TOMCAST has existed at one level or another in the tri-state area since 1988. The development of warm, wet weather diseases such as early blight, Septoria leaf spot, and anthracnose are monitored at each site using environmental recording instruments such as Campbell Scientific CR10 or Omnidata Datapod units. The original issue data loggers were Omnidata Datapods, which recorded leaf wetness and air temperature hourly but required manual downloading. The CR10 performs all Datapod functions and has the advantage of greater electronic sophistication, expansion for additional sensors, and the ability to download collected data over a phone line to an office personal computer. The CR10 units are designed with a high degree of automation and a low degree of maintenance, conserving valuable man hours for other field tasks. Clearly defined durations of leaf wetness and temperature result in the accumulation of Disease Severity Values (DSV). When specific DSV thresholds are exceeded, growers are advised to initiate spray treatments to protect the crop from fungal disease. This is how TOMCAST operates in the Midwest; as a mechanism for growers to consistently manage disease pressure.

Until mid-season 1995, late blight was the only major fungal disease of processing tomatoes TOMCAST was not designed to predict. This capability was gained by adding electronic tipping rain buckets to existing CR10 units and acquiring late blight software (BLITECAST module of WISDOM). There are currently nine CR10 units providing late blight prediction information within the tri-state TOMCAST network, in addition to disease prediction for early blight, Septoria leaf spot, and anthracnose.

There were six main objectives for TOMCAST in 1996:
1. To obtain needed late blight hardware and software
2. Initiate late blight prediction network
3. Integrate TOMCAST and BLITECAST into one comprehensive disease management system
4. To determine if TOMCAST can be adapted as a reliable disease management system for control of early blight, Septoria leaf spot, and anthracnose in fresh market tomatoes.
5. To compare calendar spray program with TOMCAST spray program at Hillsboro, OH
6. To compare TOMCAST DSV accumulation at 5 network sites with those generated by Skybit, Inc.

Introduction:

The distribution and operational set up of each CR10 and Datapod unit to their field location was completed the last week in May. June 1, all sites in the TOMCAST network began recording and reporting daily DSV for early blight, Septoria leaf spot, and anthracnose. Three fresh market sites were added to the network in 1995.

Late blight prediction was also scheduled to start June 1, but was delayed until late June due to equipment shortage. Although late blight was not detected in Ohio this year, the BLITECAST model eventually issued warnings at all stations from June 30 to July 21, based on weather data. Several states around Ohio did experience late blight this year (Table 1), including a small pocket confirmed on potatoes in southwest Michigan in late summer. Some of the temporal variability between the initial warnings among sites may be explained due to the wide geographic area covered by the network. Another factor is the non-uniform BLITECAST start date throughout the network, ranging from May 30 to June 27. It took 25 days on average to develop the first late blight warning, with the range for all sites between 7 and 59 days.

Once the late blight program was up and running, its Severity Values (SV) were reported daily along with the DSV data. DSV and SV information is summarized by site and year (Table 2). Ten TOMCAST sites did not change from 1994 to 1995, of which nine had mean accumulations 38 DSV higher in 1995 than the previous year, which translates roughly into two additional sprays in 1995 over the previous year. The variability between sites ranged from 20 to 59 DSV higher at the same location over the two seasons. Only Lacrosse, IN had 17 fewer DSV in 1995 compared to 1994.

TOMCAST and Skybit, Inc.

A research agreement between OSU and Skybit, Inc. was initiated June 1 to determine if DSV could be accurately generated at a specific field site using remote sensing technology and National Weather Service data, as an alternative to use of a CR10 or Datapod stations. Skybit, Inc. is a commercial ag-weather service, who offer custom weather products and variables for crop consultants, growers, etc.

Skybit did not generate a true DSV variable for the study, instead they supply the weather variables needed (hourly leaf wetness and air temperature) to construct daily DSV. Delivery of this information is daily, either through electronic mail or FAX. TOMCAST generated DSV were used as a benchmark to compare Skybit generated DSV on a daily basis at each of five locations to see if a difference in accumulation existed. If a difference does not exist, growers located outside the predictive range of the nearest TOMCAST site may choose to subscribe to Skybit to obtain data similar to an in-field located CR10 station.

Using a t-Test (alpha 0.05) to compare daily DSV accumulations between Skybit and TOMCAST (Table 3), found four out of five sites significantly different in their seasonal total of DSV, with Skybit predictions consistently lower. Lacrosse, IN was the only site where no significant difference was found. The lack of accumulation of nearly 60 DSV (3-4 sprays) at some sites could allow significant disease pressure to develop unchecked, resulting in yield reduction. Use of remote weather forecasting for disease prediction has potential applications for models such as TOMCAST, but needs greater development and accuracy to be adopted widely.

Fresh Market Tomatoes

Traditionally TOMCAST has been utilized by tomato processors, but this year three fresh market sites tested various aspects of TOMCAST. Previously, results from experimental plot work at Celeryville (1993) and a split field trial at two grower locations in Meigs county in 1994 indicated TOMCAST could be adapted for use in fresh market tomatoes. To further evaluate TOMCAST usefulness in a fresh market situation, a comparison of a calendar versus TOMCAST spray program was made in Hillsboro, OH. The experiment used the variety Mountain Fresh in a split field design with 10 replications. Five plants were harvested per replication. Results for early harvest (first) and total harvest are presented in Table 4 and 5. There were 6 sprays with TOMCAST versus 9 sprays under the calendar program. Sprays began June 15 and ended September 12. There was no significant difference in the number or weight of US#1 fruit and culls for either early or total harvest. This agrees with the previous year's findings which indicate that the TOMCAST spray program has not had a deleterious effect on marketable yield.

In Geauga County, growers found TOMCAST helped them time their sprays much better than in previous years. With the weather switching from wet and cool to very dry, there was much confusion on proper timing, which TOMCAST helped to eliminate. Disease pressure was low as indicated by a comparison of fruit harvested from sprayed and unsprayed plots (Table 6). Visual ratings for incidence of disease showed little difference between treatments.

Table 6. Total Harvest (Mean of 10 feet of row).

Treatment#1 Fruit (lbs)Visual Disease Rating*
Sprayed26.54.2
No Spray24.54.7
*Average of 4 dates using Horsiall-Barratt Disease Rating Scale.

Cooperator Survey Results

A nine question survey was sent to ten growers in the network to determine how important TOMCAST was to their business. The seven respondents indicated they used the TOMCAST DSV Hotline at least once a week, made most of their calls in August and July respectively, would be willing to pay $15-50 per month if TOMCAST were a commercially owned service, and rated TOMCAST 7.4 on a scale from 1 to 10 on importance to overall disease management. The cooperators also indicated they would like daily or weekly rainfall and Colorado Potato Beetle emergence data added to their site if possible.

Fresh market growers in Meigs county, not part of the above mentioned survey, are following TOMCAST and seem to be comfortable with it especially in the early part of the season. As is processing tomatoes, the early season seems to be the best time of the year to save sprays. In this region, during mid and late season, DSV accumulation on a weekly basis was the maximum that could be accumulated on several occasions.

Conclusion

TOMCAST is ultimately a successful IPM program with respect to disease management. Since 1988, the network has expanded both the number of sites and its degree of sophistication. Data collection is now almost fully automated, streamlining the information flow from the field to a central location where it can be accessed 24 hours a day via a phone by any individual. In addition to disease forecasting, the research focus will be to expand the insect component and be able to provide a total IPM approach to growing tomatoes. The use of remotely sensed weather data to generate and predict DSV and SV also holds exciting promise. Based on survey results, clientele who use TOMCAST seem very pleased with the way the system operates, and view it as a valuable service to their business. New educational materials are being developed to familiarize growers with the improved and expanded services, such as the addition of late blight forecasting via BLITECAST. These new materials will explain the combined forecasting of early blight, Septoria leaf spot, anthracnose and late blight. A very thorough explanation can be found in the 1996 Ohio Vegetable Production Guide. To keep growers abreast of any fungal disease developments, a weekly summation of DSV and SV accumulation at all TOMCAST sites will be posted in the 1996 VegNet newsletter/FAX.

Acknowledgements

Without the support and enthusiasm of a handful of county extension agents and station managers, TOMCAST would not be as diverse or encompassing as it currently is. Special thanks to Brad Bergefurd, Mardy Townsend, Hal Kneen, and Ken Scaife for all their efforts.

For further information contact Jim Jasinski , Extension Agent, Ohio State University Extension, Southwest District or the Ohio IPM Office.

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