Implementation of a Disease Forecasting System for Tomatoes in Northern New Jersey

Implementation of a Disease Forecasting System for Tomatoes in Northern New Jersey

Summary

Summary
This project has been directed at developing a viable approach to disease forecasting even under heavy and diverse disease pressures. The 1997 research confirmed that important fungal diseases affecting New Jersey’s tomatoes can be controlled, and marketable yields sustained, while fungicides are reduced dramatically.

The premise behind disease forecasting is that fungicides can be applied as needed, when disease development is likely, rather than being applied according to the calendar. Using forecasting methods reduced production costs for growers and the environment benefits from reduced pesticide use. This project continues to evaluate and develop the use of the TOM-CAST system for forecasting tomato diseases in northern New Jersey.

Objectives
* Continue evaluations of tomato disease forecasting as an alternative approach to disease control for fresh market tomato production in northern New Jersey by conducting field research to specify thresholds for using the TOM-CAST system under different seasonal weather conditions, by evaluating the impact of reduced fungicide applications with TOM-CAST on postharvest fruit quality, and by expanding the database for evaluating the economic impact on tomato production of using (TOM-CAST) as an alternative approach to disease control.

* Continue to develop the software required for weather data collection and forecast generation, evaluate weather monitoring equipment, and standardize equipment use procedures.

* Continue to investigate an electronic meteorological service as an alternative to on-site weather monitoring.

* Continue grower research demonstrations, and continue to explore means for delivery of disease forecasts.

* Generate the information, including the economic data, needed to determine how disease forecasting might best be implemented by individual growers or provided by organizations such a grower cooperatives or by programs such as Rutgers Vegetable IPM program.

Abstract
The use of forecasting for tomato disease control in northern New Jersey has been under evaluation since 1991. The basic premise behind disease forecasting in crop production is that fungicides are applied as needed, when disease development is likely, rather than by conventional calendar-based scheduling. This allows for potential reductions of chemical inputs while maintaining crop quality and yields. The potential benefit to growers is lower production costs; the benefit to the environment is reduced pesticide applications during crop production and reduced potential for environmental pollution.

The TOM-CAST forecast system was shown to have important advantages over other systems, in that it was more user friendly and maximized reductions in spray schedules while providing adequate disease control. The 1998 SARE/ACE research trial, conducted at the Rutgers Snyder Research and Extension Farm, focused on evaluating fungicides and combinations of fungicides in conjunction with TOM-CAST using the decision thresholds defined during trials in previous years. All evaluated fungicides reduced foliar disease, whether on a weekly or TOM-CAST schedule. Control with the TOM-CAST schedule was somewhat less than with the weekly schedule. Quadris, azoxystrobin, a relatively new fungicide chemistry, used in alternation with Bravo Weatherstik, chlorothalonil, a widely used fungicide, provided the best disease control on both a weekly or TOM-CAST schedule. Nucop 3L was least effective with the TOM-CAST schedule. Five TOM-CAST scheduled applications resulted in total and marketable yields statistically equivalent to yields resulting with 15 conventionally scheduled applications for all fungicides except Champ 2F.

Under research trial conditions of high disease pressure from a new, powdery tomato mildew, most materials controlled disease adequately with TOM-CAST schedules that reduced the number of sprays by 67%. The 1998 research trial confirmed that disease forecasting is a sustainable alternative approach to disease management in tomato production. By following TOM-CAST during the 1998 season, 22.5 lb per acre of fungicide active ingredient (assuming use of Bravo Weatherstik at 3 pts per acre per spray) could have been eliminated from tomato production.

Disease forecasts were available to tomato growers in northwestern New Jersey in 1998. Over 50 growers were instructed on the use of TOM-CAST at the North Jersey Vegetable Growers Meeting in February 1998. Printed information was also distributed. During 1998, thirteen growers received TOM-CAST forecasts by fax or from IPM scouts.

In 1997, data from six on-site weather stations was compared with data from SkyBit, an electronic meteorological service, for the same sites. This comparative research was replicated in 1998. In 1997, SkyBit data generally provided a more conservative TOM-CAST forecast than did on-site data due to differences in both leaf wetness and temperature. Data variation has been attributed to consistent errors in the systems, to some random error, and to specific conditions at a given site. TOM-CAST is not very sensitive to inputs, which increases the potential for electronic weather data being useful in this system. The use of weather data from a subscription service would eliminate the need for forecast providers to buy and maintain weather stations and the computer systems needed to access them. It would also make do-it-yourself forecasting affordable and feasible for growers. Analysis of the 1998 data will clarify whether or not an electronic weather service will be a viable source of weather information for TOM-CAST.

Specific Project Results
A field trial at the Snyder Research and Extension Farm evaluated various fungicides and combinations of fungicides with TOM-CAST using decision thresholds defined in previous research trials. Weather data for generating the TOM-CAST forecast was obtained from an on-site field monitor from sensor instruments, the same equipment used at grower sites. Bravo Weatherstik (3 pt. per acre), Quadris alternating with Bravo (0.6 oz or 3 pt. per acre), Champ 2F (1.5 to 2.5 pt. per acre), Champ 2F and Bravo Weatherstik (1.5 pt. per acre of each), NuCop 3L (1.5 to 2.5 pt. per acre), NuCop and Bravo Weatherstik (1.5 pints per acre) or Manzate 200DF then Bravo 720 (3 lb, 3 pt. per acre) were applied on weekly or TOM-CAST schedules. Foliar disease was visually rated each week beginning in mid-August when foliar damage was first observed. Fruit was harvested weekly and total and marketable weight recorded.

Disease incidence was heavy throughout the field by the end of the season, with the most prevalent foliar diseases being early blight, the most serious foliar fungal disease of tomatoes in New Jersey, and a powdery mildew. The weekly schedule resulted in 15 applications; the TOM-CAST schedule called for five applications. Disease ratings on September 23 indicated that all fungicide treatments reduced foliar disease compared to the untreated control. Quadris alternating with Bravo on the weekly or TOM-CAST schedule was better than any other treatment. Control with the TOM-CAST schedule was somewhat less than with the weekly schedule for all fungicide treatments. NuCop 3L was least effective with the TOM-CAST schedule. Total yields were not affected by fungicide or schedule. No fungicide treatment increased marketable yields compared to the control. Marketable yield was not affected by schedule for any fungicide except Champ 2F. Weekly applications of Champ 2F or NuCop-Cop 3L actually reduced marketable yields.

The 1998 trial provided important evidence, expanding on that from previous years, that disease forecasting is a viable approach to disease control. In the presence of powdery mildew, a new disease on field tomatoes in New Jersey, the TOM-CAST schedule provided enough control to maintain marketable yields. Reducing the number of fungicide applications by almost 70% would benefit growers through reduced costs of disease control and benefit the environment through reduced chemical inputs.

A procedure for calibrating and monitoring on-site weather equipment, begun in 1997, was continued in 1998.

The 1997 comparison between on-site field monitor data and data obtained through subscription to the electronic meteorological service, SkyBit, Inc., found that SkyBit temperature readings were lower on average at all sites. Leaf wetness readings were in agreement two-thirds of the time, but totals were lower at most sites. SkyBit data generally provided a more conservative TOM-CAST forecast than did on-site data due to the differences in both leaf wetness and temperature. Analysis of the 1998 weather data from these sources for the same sites will clarify whether an electronic weather service will be a viable source of weather information for TOM-CAST.

The grower-demonstration component of the project was eliminated in 1997 when the decision was made to offer TOM-CAST forecasts to the tomato growers in northwestern New Jersey. In 1998, six field monitors were deployed in an area of approximately 400 square miles to collect weather data needed for TOM-CAST. Forecast information was updated twice weekly from May 1 to October 15 and provided to growers by an AT&T Digital Answering System and by fax on request. In 1998, TOM-CAST forecast information was also available through the Rutgers Fax Info Line and as part of the Rutgers Cooperative Extension Vegetable IPM Tomato Program. Fifty growers were instructed in the use of TOM-CAST at the North Jersey Vegetable Growers Meeting in February 1998.

Of 21 surveys sent to growers who received training instruction and information on TOM-CAST in 1997, 15 were returned. Ten growers did not use TOM-CAST in 1997 for a variety of reasons including crop failure, small acreage, no on-farm weather station, inconvenient phone-in, laziness, and lack of information. Of the five growers using TOM-CAST, three provided actual spray records indicating they made 52% fewer sprays as compared to a conventional seven-to-ten-day schedule. Resulting cost savings were estimated at $295 per acre. Chemical inputs were reduced by an average 15.75 lb. per acre, assuming use of chlorothalonil at 2.25 lb. active ingredient per acre per spray.

A survey mailed to growers in late 1998 will clarify the economic and practical advantages and disadvantages of using disease forecasting in commercial tomato production. The estimated costs of Rutgers Cooperative Extension providing forecasts to growers in 1997 were presented at a discussion of vegetable integrsted pest management on December 16, 1997.

Dissemination of Findings
The 1997 grower survey results were presented at the New Jersey Vegetable Growers Meeting, January 21, 1998, in Atlantic City, at the North Jersey Vegetable Growers Meeting, February 9, 1998, in Pittstown, New Jersey, and at the 1998 International Conference of the American Society of Horticultural Science, July 11 to 15, in Charlotte, North Carolina. During 1998, information about TOM-CAST and forecast summaries were published in Rutgers Cooperative Extension Plant and Pest Advisory Newsletter, which is disseminated statewide. The 1998 research trial was discussed at the North Jersey Research Results Twilight Meeting, September 2, 1998, and the results presented at the Annual Mid-Atlantic Vegetable Workers Conference, November 3 and 4, in Newark, Delaware. Written reports will be submitted to that proceedings and for publication in APS’ Fungicide and Nematicide Tests, Volume 54, and to Vegetable Plant Pathology Research Results Report, Rutgers Research and Development Center, Bridgeton. Reports and summaries will be posted on the SARE Tomato World Wide Web page at http://www.virtualorchard.net/tomato/ as downloadable PDF files and as html files. A manuscript will be prepared in 1999 for submission to a refereed journal.

Reported December 1998. 1999 Northeast Region SARE/ACE Report.