Working Toward Implementation of a Disease Forecasting System for Fresh Market Tomatoes in Northern New Jersey

Final Report for ANE96-030

Project Type: Research and Education
Funds awarded in 1996: $0.00
Projected End Date: 12/31/2000
Matching Non-Federal Funds: $74,130.00
ACE Funds: $54,210.00
Region: Northeast
State: New Jersey
Project Leader:
Winfred Cowgill
Rutgers University
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Project Information


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 potentially allows chemical inputs to be reduced while maintaining crop quality and yields. The potential benefit to growers is lower production costs and to the environment is reduced pesticide applications during crop production and reduced potential for environmental pollution.

The TOM-CAST forecast system, developed in Ontario, Canada by Ron Pitblado, had been shown, in work prior to 1996, to have important advantages over two other tomato disease forecast systems, FAST (Pennsylvania State University) and CUFAST (Cornell University). It was more “user friendly” and maximized reductions in spray schedules while providing adequate disease control. The 1996 and 1997 SARE/ACE research trials conducted at the Rutgers Snyder Research and Extension Farm in Pittstown, NJ, focused on defining and confirming decision thresholds for using TOM-CAST in northern New Jersey. In 1997 and 1998, field trials also focused on efficacy of various fungicides in conjunction with TOM-CAST. An investigation of weather data source in relation to disease forecasting was also begun in 1996 and continued through 1999.

In three years of field trials supported by the SARE/ACE program, TOM-CAST reduced the number of fungicide applications needed for disease control by 62% and maintained marketable yields. This reduction resulted in 63 pounds per acre of chlorothalonil, a widely used fungicide, being eliminated from tomato production inputs for this period. Extrapolating this data to the estimated 300 acres of fresh market tomatoes in three northern New Jersey counties (NJ Agricultural Statistics, 1997), TOM-CAST would have eliminated more than nine tons of chlorothalonil from tomato production.

The 1997 and 1998 field trials evaluated the efficacy of certain fungicides (in addition to chlorothalonil) for use with TOM-CAST. Champ 2F plus Bravo 720, Manzate 200DF switching to Bravo – a regimen in use by growers – and Quadris, azoxystrobin, a new fungicide, used in alternation with Bravo Weatherstik (chlorothalonil) controlled disease with a TOM-CAST schedule. These results allow growers using TOM-CAST to choose the fungicide that best suits their needs and budget.

Three years of comparing on-site weather data with data from SkyBit, Inc., an electronic meteorological subscription service, confirmed that SkyBit data generated forecasts similar to or more conservative (called for more sprays) than on-site data forecasts. SkyBit subscription would be a viable and reasonably priced alternative to on-site weather monitoring for growers. In 1999, tomato disease forecasts were provided by the Rutgers Vegetable IPM program to growers in northern New Jersey who subscribed to SkyBit. On-site monitoring at three farms using TOM-CAST during 1999 confirmed the findings of the previous three years.

The 1996 grower demonstration of disease forecasting included five farms in a 400 square mile area. That year, three grower/cooperators who provided spray records reduced fungicide sprays by an average 14 percent on the TOM-CAST plots compared to their conventionally treated plots. They reported no difference in foliar disease damage or incidence of fruit anthracnose. In 1997, Rutgers cooperative Extension (RCE) offered TOM-CAST forecasts to all growers in a five county area. The forecasts were provided by fax to six growers and were also available by phone message. Three growers who followed the forecasts and reported their spray records reduced fungicide inputs by an average 56 percent compared to a weekly schedule. In 1998, forecasts were provided by fax to eight growers and posted by RCE IPM scouts at three additional locations. Four growers who followed the forecasts and provided spray records reduced fungicide inputs by an average 61 percent compared to a weekly schedule. Calculated TOM-CAST spray schedules for the 1999 season indicated a potential 50 percent reduction in number of fungicide applications on the monitored sites.

Our SARE/ACE supported research confirmed that forecast scheduling of early blight and anthracnose control using TOM-CAST is a viable alternative strategy for northern New Jersey tomato growers. Fungicide inputs can be reduced without undue risk to the crop or loss of marketable yield, resulting in considerable savings in pesticide inputs to the environment and in cost savings for growers. To date, grower adoption of disease forecasting has been limited, but those growers who used forecasting in 1997 and 1998 cited reducing cost, pesticide exposure and crop residue and “guess work” in spray scheduling as advantages of using TOM-CAST. In 1999, tomato disease forecasts were provided by the RCE Vegetable IPM Program to growers who subscribed to SkyBit for weather data. Disease forecasting was no longer free to growers, and use of disease forecasting declined somewhat. With continuing grower education, adoption of disease forecasting for tomatoes should increase over the coming years as has adoption of other RCE IPM management practices in New Jersey, notably among fruit growers.

Project Objectives:

1. Continue evaluations of tomato disease forecasting as an alternative approach to disease control for fresh market tomato production in northern New Jersey by:

a. conducting field research to specify thresholds for using the TOM-CAST system in northern New Jersey under different seasonal weather conditions;
b. evaluating the impact of reduced fungicide applications with TOM-CAST on postharvest fruit quality;
c. expanding the data base for evaluating the economic impact on tomato production of using disease forecasting (TOM-CAST) as an alternative approach to disease control.

2. Continue to:
a. develop the software required for weather data collection and forecast generation;
b. evaluate weather monitoring equipment;
c. standardize equipment use procedures.

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

4. Continue grower research demonstrations; explore means for delivery of disease forecasts.

5. Generate the information, including 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.


Materials and methods:

Northern New Jersey is an area of rolling hills and wooded areas with a humid, temperate climate. Tomato fields are relatively small and often surrounded by woods. Elevation and restricted air flow can influence disease development conditions. It was important to document effects of topography on the forecasts generated by TOM-CAST. During the 1997 season, the number of sprays called for ranged from four to eight among the six weather monitoring sites. In 1998 forecasts for sites varied from six to ten and in 1999 from three to five for the season. Variability among sites confirmed the need for site specific forecasts in northern New Jersey.

Research results and discussion:

1. The 1996 field trial provided data for a final determination of decision thresholds for using TOM-CAST. Sprays would be initiated when 25 disease severity values (DSV), generated by the forecast model, accumulated from time of transplanting and repeated every time an additional 15 to 20 DSV accumulated since a spray. We showed that delaying initial sprays to 35 DSV did not adequately control disease in all years. Although a respray interval of 25 had been effective in controlling disease and maintaining marketable yield, the conservative respray range of 15 to 20 DSV was selected. This would allow growers leeway in using forecasts without jeopardizing disease control and without a large increase in total number of sprays. These thresholds were reconfirmed in the 1997 and 1998 trials evaluating the efficacy of selected fungicides with TOM-CAST.

Research results prior to 1996 had raised concern about adverse effects of reduced fungicide schedules on postharvest disease control. The 1996 and 1997 trials confirmed that using TOM-CAST on staked culture tomatoes did not increase postharvest disease losses. The value of staking for foliar and postharvest disease control was demonstrated by this research.

In three years of research trials, marketable yields were maintained while fungicide applications were reduced by 62 percent. A reduction of 28 sprays (compared to weekly schedules) was achieved. On a per acre basis, this reduction would have eliminated 63 lbs. of fungicide active ingredient from tomato production inputs. Using data provided by Robin Brumfield, Specialist in Farm Management, Rutgers Cooperative Extension, (Brumfield, Effiom and Reiners. 1994. Acta Horticulturae 340:255-266; Brumfield. 1998) cost saving from eliminating fungicide applications was estimated at $36.25 per acre per spray (labor, equipment and chlorothalonil). An annual average savings of $325 per acre was projected. This is 6.7 percent of 1996 production costs per acre in the Northeastern US of ICM managed fresh market tomatoes (Brumfield) with costs of staking added.

An added objective of the 1997 and 1998 trials, evaluating efficacy of various fungicides, confirmed that certain fungicides commonly used by growers as well as a new fungicide could be used effectively in conjunction with TOMCAST, allowing growers some choice in materials, including lower cost options. The 1998 trial also provided important evidence, expanding on that from previous years’ trials, that disease forecasting is a viable approach to disease control in the presence of some other diseases. Although powdery mildew, a new disease on field tomatoes in New Jersey, was severe on untreated plots, TOM-CAST scheduled treatments provided disease control adequate to maintain marketable yields.

2. A procedure for calibrating and monitoring on-site weather equipment, begun in 1997, was followed in 1998 and 1999. Since use of TOMCAST was dependent on on-site weather stations, equipment was regularly maintained and monitored; backup equipment was available. Accessing the weather information and generating useful data in an efficient way required use of computers and specially developed computer programs. It become evident during the course of the project that the time and expense involved in dealing with equipment and data would probably not be feasible for most northern New Jersey growers or for the Rutgers Vegetable IPM Program to bear. An alternative to on-site weather monitoring was viewed as being important to implementing tomato disease forecasting for northern New Jersey.

3. Three years of on-site Field Monitor™ weather data and SkyBit, Inc. (P.O. Box 10, Boalsburg, PA 16827-0010) electronic simulated weather data for several northern New Jersey sites were compared. In all years, SkyBit temperature readings corresponded closely to Field Monitor readings but were lower, on average, at most sites in both years. SkyBit cumulative leaf wetness estimates were, on average, about 20 percent different from Field Monitor estimates, in most cases being lower. However, total disease severity values based on SkyBit data were the same as or higher than those based on Field Monitor data. As a result, TOM-CAST spray schedules based on SkyBit called for more sprays than those based on Field Monitor data. However, the insensitive nature of the TOM-CAST system tended to mitigate the differences between SkyBit and Field Monitor temperature and leaf wetness data, and the spray schedules over the three years differed by an annual average of two sprays. Use of TOM-CAST based on SkyBit would have called for an average eight applications for the typical tomato growing period, a 50 percent reduction compared to approximately 16 sprays following a conventional seven to ten day schedule. After three years of evaluation, SkyBit E-Weather Service was deemed to be a viable, practical alternative to on-site weather monitoring for using TOM-CAST in northern New Jersey.

4. Grower demonstrations took place on five farms in 1996, expanding on previous years demonstrations. Three growers followed forecasts on small sections of their tomato acreage and reduced sprays by an average 14 percent compared to their conventional practice. They reported no or little difference in disease control. The grower demonstration component of the project was eliminated in 1997 when the decision was made to offer TOM-CAST forecasts to all tomato growers in northwestern New Jersey. In 1997 and 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 AT&T Digital Answering System or by fax. 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. In 1999, TOM-CAST forecasts were generated from SkyBit data and provided by the Rutgers Vegetable IPM Program to growers who requested them and subscribed to SkyBit, Inc.

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; acreage too small; weather station not on farm; phone-in inconvenient; laziness; did not have information. Of the five growers using TOM-CAST, three provided actual spray records indicating they made an average 56 percent fewer fungicide applications as compare to a weekly schedule. Surveys return by seven of the eleven growers who received forecasts in 1998 indicated that five used the forecasts on 100 percent of their tomato acreage. They reduced fungicide applications by an average 61 percent compared to a weekly schedule.

5. It was shown, based on research trials and grower experience, that growers in northern NJ could reduce the cost of producing fresh market staked tomatoes by using TOM-CAST to schedule fungicide applications. Average annual savings per acre ($325.00) realized from reducing fungicide applications was nearly seven percent of average total production costs. But, costs associated with establishing and maintaining on-farm weather stations were viewed as prohibitively high for growers. Rutgers personnel worked with SkyBit, Inc. so that TOM-CAST forecasts could be provided directly to growers at reasonable cost. The annual cost of subscribing to SkyBit to receive the TOM-CAST forecasts (approximately $300.00 for five months) is less than the savings that might be realized on one acre of tomatoes in one year. A basic SkyBit subscription provides growers with other potentially valuable information, such as daily summaries and forecasts of several weather parameters, in addition to TOM-CAST.

Participation Summary


Educational approach:

From 1996 to 1999, the findings related to this research were presented regularly at: the Annual Mid-Atlantic Vegetable Workers Conference; International Conference of the American Society of Horticultural Science ; North Jersey Vegetable Growers Meeting; North Jersey Vegetable Twilight Meeting. Additional research presentations were: 1997, the 13th Annual Tomato Disease Workshop; 1998, the New Jersey Vegetable Growers Meeting.

Written reports have appeared in: Proceedings of the Mid-Atlantic Vegetable Workers Conference; Proceedings of the 13th Annual Tomato Disease Workshop; Vegetable Plant Pathology Research Results Report, Rutgers Research and Development Center, Bridgeton; APS’ Fungicide and Nematicide Tests Volume 54. Information about TOM-CAST and forecast summaries were published in Rutgers Cooperative Extension Plant and Pest Advisory. A manuscript is being prepared for submission to HortTechnology in 2000. A manual on TOM-CAST and its use was developed and distributed to growers in 1997, 1998 and 1999.

Project Outcomes

Impacts of Results/Outcomes

The basic premise behind development and implementation of disease forecasting in crop production is that disease control materials can be applied “as needed” rather than on a calendar-based schedule, affording the possibility of reducing chemical inputs while maintaining crop quality. Several years’ evaluation by Rutger’s researchers of forecasters developed for early blight and anthracnose control on tomato have demonstrated that reducing disease control inputs is possible. Benefits accrue to the grower in lower production costs and to the environment in reduced amounts of pesticide applied during crop production. For six years of field trials with TOM-CAST, which included the SARE/ACE supported work, and using thresholds defined by those trials, fungicide applications were reduced by and an average 65 percent with no serious adverse impact on disease control and no adverse impact on marketable yields. During that time, 130 lb. per acre of fungicide active ingredient (assuming use of Bravo Weatherstik, 3 pt/acre) would have been eliminated from production inputs. Extrapolating to the 300 acres of fresh market tomatoes grown in northern New Jersey (1997), almost 20 tons of pesticide would have been eliminated from crop production over that time period.

Pesticide Reduction

Bravo Weatherstik (formerly Bravo 720), chlorothalonil, is a general use fungicide for control of tomato early blight and anthracnose fruit rot. The recommended application rate is 3 pt/acre per application. The 1996-98 research trials achieved a 62 percent reduction in fungicide input. Average annual reduction for six years of trials was 65 percent. Extrapolating to the 300 acres of fresh market tomatoes grown in northern New Jersey (1997), almost 20 tons of pesticide would have been eliminated from crop production over that six year period.

Economic Analysis

Costs were estimated at $36.25 per spray per acre based on data from Robin Brumfield (1996). Estimated annual per acre savings from using TOM-CAST to schedule fungicide applications, based on these research trial results, were calculated at $325.00. This savings is almost seven percent of the average per acre cost of producing fresh market ICM managed fresh market tomatoes in the northeast (Brumfield, 1996) with the cost of staking added. The average annual cost savings on one acre of tomatoes could cover the $300.00 cost (in 2000) of subscribing to SkyBit for five months.

Farmer Adoption

Changes in Practice

Two of three 1996 grower/cooperators gave positive responses to the question “would you consider adopting this practice [disease forecasting] on your entire crop in the future.” In 1997, three of the five growers who received TOM-CAST forecasts reported reducing fungicide applications by an average 56 percent. In 1998, at least 13 growers received TOM-CAST forecasts. Four growers who reported their spray schedules reduced fungicide applications by an average 61 percent. In 1999, TOM-CAST forecasts were no longer provided free of charge and use declined. For those farms requesting forecasts, a potential 50 percent reduction in number of fungicide sprays was calculated. In 2000, TOM-CAST will be directly available to growers by subscription to SkyBit, Inc., increasing the convenience for growers. Continuing education about disease forecasting by Rutgers Cooperative Extension will be needed to encourage wider adoption.

Operational Recommendations

Based on research trial results and growers’ experiences, disease forecasting can be recommended to tomato growers in northern New Jersey as a tool that, used in conjunction with recommended standard production practices such as crop rotation and staking, can optimize fungicide use. Participation in the Rutgers Vegetable IPM program, which provides disease scouting, is considered desirable. In most years growers could expect to reduce fungicide use, save costs and time while maintaining crop yield and quality.

Producer Involvement

Number of growers in attendance:
Twilight Field Meetings – 115
Annual Grower Meetings – 170
Annual Vegetable Growers Conference – 50

Farmer Evaluations

Fifteen of twenty-one grower surveys were returned in 1997. Peter Melick, a second year tomato grower who had previously expressed considerable skepticism about using a forecast system, found the forecasts were ”…something to go by” and followed them closely. Mark Philips, demonstration cooperator, used the forecasts as a general guide but concluded that the disease conditions on his site were too severe to follow the forecasts successfully. Greg Scibilia, long time cooperator on disease forecasting, also used the forecasts as a general guide. In his view, forecasting “…is the future…,” grower confidence will increase with time, and even small savings are worthwhile from an economic and environmental standpoint. Bill Maxwell, a grower new to disease forecasting, indicated that he was too busy to spray on a schedule determined by someone else. Gary Donaldson, demonstration cooperator, did use the forecasts as an aid to scheduling, stretching the intervals between applications, but he noted that following the forecast complicated overall scheduling of spray operations. Growers not using the forecasts cited a number of reasons including: : crop failure; acreage too small; weather station not on farm; phone-in inconvenient; laziness; did not have information about TOM-CAST.

Seven of eleven growers returned surveys for the 1998 season. Five growers used the forecasts on all of their tomato acreage. The advantages cited were: reduced spray applications, resulting in less cost, less exposure [to pesticide] and less [pesticide] residue; reduces “guess work [in scheduling]; confirms need for disease control, especially in “bad” years. Some disadvantages noted were: some inconvenience of irregular spray schedule; occasional lack of timeliness in receiving forecasts; temptation to add fungicide when making other pesticide applications. One grower cited “no time” and dry conditions as reasons for not using the forecasts.

Areas needing additional study

Information from the 1997 survey of growers who were contacted and educated about the use of TOM-CAST suggests that additional education and support may be needed to encourage grower adoption of disease forecasting in tomato production. The decreased grower use of TOM-CAST in 1999 when the forecasts were no longer free suggests that direct financial subsidies may be important in encouraging adoption of new practices that result in some initial cost to growers. A study of this issue may be warranted.

The development of new disease forecast systems requires, as an essential first phase, fundamental research leading to development of the disease model. Support for this research would encourage the development of forecast systems for diseases that are currently being controlled with conventional, calendar-based spray schedules.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.