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Project description

Disease Forecast Model for Controlling Blackmold in Tomato. (97BU011)
Program UC IPM competitive research grants program
M.D. Cahn, Cooperative Extension, Sutter/Yuba counties
R.M. Davis, Plant Pathology, UC Davis
Host/habitat Tomatoes
Pest Blackmold Alternaria alternata
Discipline Plant Pathology
Biorational Use of Biotic Agents or Chemicals
Start year (duration)  1997 (Two Years)
Objectives Develop a computer-based, disease forecast system to optimize fungicide timing for controlling black mold (Alternaria alternata) in tomato.

Determine the period for A. alternata infection under different regimes of relative humidity, leafwetness, and air temperature.

Evaluate timing of fungicide application on control of black mold disease.

Develop and validate a forecast model for black mold disease.

Tomato fields located in the south Sacramento Valley were monitored for blackmold disease during July-October of the 1998-growing season. Weather conditions, including relative humidity, and air temperature and leaf wetness, were also monitored to identify the conditions that promote disease. Data collected during the 1998-growing season will be used to validate and/or modify a preliminary disease forecast model that was developed from data collected in previous seasons.

Fungicide field trials were conducted at three locations to examine the effect of application timing and number of applications on blackmold disease control. The Sutter County trials had few significant differences among treatments. However, results from the Yolo County site showed that timing of fungicide applications significantly affected disease control. Fungicide sprayed six and four weeks before harvest provided the best disease control.

Laboratory and greenhouse experiments were conducted to determine environmental conditions that promote blackmold disease of tomato fruits. The results of these experiments showed that maximum fruit infection occurred after 12 hours of continuous exposure to free moisture. Fruits that were ripe longer than 10 days were most susceptible to blackmold disease. Infection was found to occur under relative humidity as low as 60%.

Results from spray trials and incubation studies will aid the development and validation of a disease-forecast model that growers will be able to use to time fungicide sprays.

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