UC IPM Online UC ANR home page UC IPM home page

UC IPM Home

SKIP navigation

 

Research and IPM

Models: Diseases

Crop: Carrot

Disease: Alternaria Leaf Blight
Pathogen: Alternaria dauci

Note: Before using a model that was not field tested or validated for a specific location, the model should be tested for one or more seasons under local conditions to verify that it will work in this location. See "Validation Work" below.

Model 1 of 3

Model developer and citation

Mike Davis and Joe Nunez. Investigations into the Cause and Control of Carrot Root Forking, Cavity Spot, and Leaf Blights. California Fresh Carrot Advisory Board 1995 Annual Report. P. 57-68.

Sensor location

10 cm above soil surface in crop canopy.

Input variables

Environmental: Air temperature, relative humidity, leaf wetness duration.

Host: Age of carrot field.

Model description

The model is based on a weekly summation of daily disease severity values (DSV). DSVs begin to accumulate eight weeks after planting.

To predict disease development one week in advance, multiply weekly DSV by 0.03 and add this to the current week's observed percent disease incidence.

  • DSV= DAP/45(Y+X).
  • DSV=daily disease severity value.
  • DAP=days after planting.
  • Y=hours of 95-100% relative humidity at 50 F or greater divided by 8.
  • X=hours of leaf wetness.

Action threshold

The determination of an action threshold is in progress.

Model validation

Validation work is being conducted in 1996 and 1997, by Mike Davis and Joe Nunez of the University of California, in Kern County.

Model implementation

The model is still in the validation phase.

Future directions of model

To develop an action threshold.

Related work

Strandberg, J. O. Spore production and dispersal of Alternaria dauci. Phytopathology 67:1262-1266.

Top of page

Model 2 of 3

Model developer and citation

Modifications by Campbell Soup Company.

Pitblado, R .E. 1992. The development and implementation of TOM-CAST: A weather-timed fungicide spray program for field tomatoes. Ministry of Agriculture and Food, Ontario, Canada.

Madden L., Pennypacker, S. P., and McNab, A. A. 1978. FAST, a forecast system for Alternaria solani on tomato. Phytopathology 68:1354-1358.

Sensor location

Not specified.

Input variables

Environmental: Air temperature, leaf wetness duration.

Calculated: Mean air temperature during the leaf wetness period.

Model description

Disease severity values (DSV) are calulated as a function of hours of leaf wetness and average air temperature during leaf wetness. The DSV is based on the FAST early blight model of tomato. After treatment, the DSV accumulations reset to zero. The accumulations of DSVs continues through September.

Action threshold

According to the model, initiate treatments when 35 DSVs have accumulated or by July 5, whichever comes first. Subsequent treatments should occur at the accumulation of 20 DSVs.

Model validation

Not known.

Model implementation

Campbell Soup Company in MI, OH, NJ, using TOMCAST.

Bolkan, H. A., and Reinert, W. R. 1994. Developing and implementing IPM strategies to assist farmers: an industry approach. Plant Dis. 78:545-550.

Top of page

Model 3 of 3

Model developer and citation

Gillespie, T. J., and Sutton, J. C. 1979. A predictive scheme for timing fungicide applications to control Alternaria leaf blight in carrots. Can. J. Plant Pathol., 1: 95-99.

Sensor location

At ground level among the carrots.

Input variables

Environmental: Forecasted temperature and leaf surface wetness duration (based on forecasts of rain, cloud cover and surface wind speed).

Calculated: Mean air temperature during the leaf wetness period.

Host

Presence of blight symptoms.

Model description

This model is based on infection indices derived from the interaction of surface wetness duration and mean air temperature during the wetness period. Surface wetness duration is determined from forecasted weather of the forthcoming 36 hours. See original reference for a table of infection indices.

Action threshold

According to the model, initiate treatments when blight symptoms appear on 1-2% of the foliage. Subsequent treatments should occur based on infection period indices of 2 or 3 (moderate or high risk of infection), after a minimum of a seven- to ten-day spray interval.

Model validation

Evaluated in CA in 1992.

Gillespie, T. J., and Sutton, J. C. 1979. A predictive scheme for timing fungicide applications to control Alternaria leaf blight in carrots. Can. J. Plant Pathol., 1:95-99.

Model implementation

Not known.

Future directions of model

To adapt model according to cultivar susceptibility; To integrate the model with Cercospora forecaster, a model of Cercospora leaf blight of carrot, when appropriate.

Related work

Sutton, J. C., and Gillespie, T. J. 1977. Relation of weather variables and periodicities or airborne spores of Alternaria dauci. Phytopathology 67:879-883.

Langenberg, W. J. 1975. Carrot leaf blight (Alternaria dauci) development in relation to environmental factors and fungicide applications. M.Sc. Thesis, University of Guelph. Guelph, Ontario. 119 pp.

Top of page


Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2005 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

Accessibility   /DISEASE/DATABASE/carrotblight.html revised: March 28, 2005. Contact webmaster.