PROJECT: Comparison of Disease Control on Fresh Market Tomatoes using TOMCAST and SKYBIT to Time Fungicide Applications FUNDS AWARDED/UTILIZED: $2400 / $2200
PRINCIPAL INVESTIGATORS: Jim Jasinski. OSU Extension SW District IPM
Mac Riedel, Pecky Lyon, Plant Pathology
Brad Bergefurd, Thom Harker, The Enterprise Center. Robert J. Precheur, Horticulture 8 Crop Science
BACKGROUND:
TOMCAST, a tomato disease forecasting program, has served the
Ohio fresh market tomato industry since 1996 by providing assistance
in scheduling fungicides. initially, DSV spray thresholds were
adapted from processing operations to meet the quality standards
necessary for fresh market product. As preliminary spray thresholds
continue to be developed and tested in the field, all her concems
such as access to TOMCAST information have emerged. Over the last
few years. far profit weather forecasting businesses began offering
local sources of Disease Severity Values (DSV) to growers. Monthly
weather forecasting contracts during the growing season may have
an economical appeal to growers vs. the large up front expense
of a local weather station. These altemate sources of agricultural
weather require investigation for both the quality and reliability
of the information broadcast.
OBJECTIVES: (1)TO compare the accumulation of DSV in Hillsboro,
OH using a ground based CR10 datalogger versus Skybit generated
values and (2) To compare the fruit quality produced by both systems
following a 15, and 20 DSV fungicide schedule.
MATERIALS AND METHODS: A Campbell Scientific GR10 datalogger
was stationed at, Hillsboro to record hourly temperature, leaf
wetness, and precipitation. Specific combinations of temperature
and leaf wetness are converted to DSV on a daily basis and accumulated
from June 1 through harvest, typically mid September. Daily forecasted
leaf wetness and temperature data were received electronically
from Skybit during the same time frame, also producing a daily
DSV. Fungicide scheduling trials an fresh market tomatoes were
conducted in 1998 at Hilisboro, OH. There were six fungicide application
treatments on tomato cultivar Mountain Spring: Skybit 15 (DSV),
Skybit 20, Tomcast 15 (DSV), Tomcast 20, 7 day calendar, and an
untreated check, each replicated fourtimes. Each treatment was
applied when the number of DSV accumulated by each system (Skybit
orTomcast/CR10) equaled or exceeded the Action Threshold (15,
or 20 DSV). weather permitting. Fruit quality was determined on
site by harvesting five feet of row perplot and analyzing the
data with a two way ANOVA. Spray schedules for the site are listed
in Table 1.
RESULTS & DISCUSSlON: DSV accumulation under both systems
are shown in Figure 1 for Hillsboro The Skybit forecasting system
generated a higher number of DSV than the CR10 datalogger physically
measured. The maximum difference between the two curves can be
seen readily by the end of June or first palt of July. From this
point on, the difference between the two systems remains constant
or even decreases over time. Since there is no consistent pattern
of accumulation, it is difficult to determine during the season
when the Skybit numbers closely follow ground based observations
and when they diverge. With a wide fluctuation in the accuracy
of the DSV accumulations compared to ground based readings, the
results were similar, especially in the area of a wide DSV gap
early in the season between the two systems, followed by unpredictable
DSV accumulations later in the season. Table i. Fungicide treatment
dates for Hillsboro tomato studies.
The Hillsboro site showed no statistical
separation between the treatments in the categories of Red plus
Green, and Salad. Cull weight of fruit in the calendar treatment
was significantly less than the cull fruit weight of Tomcast 20
DSV. Although statistically no differences were seen, the calendar
fungicide program yielded the most Red plus Green fruit and the
check the least. with the other treatments with very similar yields
(See Table 2 below).
Table 2. Yield of Fresh Market Tomato Fruit
in SKYBIT venus TOMCAST Disease Control programs.
With quality and yield being stafisticaliy
no different, growers would not have been penalized for using
(following) either TOMCAST or Skybit DSV accumulations to schedule
their fungicides, even though the two systems accumulation curves
were off by as much as 25 units at different times of the season.
Part of the lack of difference may be attributed to the weather
not allowing for sprays to be applied as soon as they were recommended,
and the second part involves the conservative nature of the DSV
calculation itself. Being "off" by a few days or a
few DSV doesn't heavily affect fruit quality or yield, according
to these experiments.