Potato Late Blight Forecast

Malheur Experiment Station

Information for Sustainable Agriculture

BLIGHTCAST

A cooperative program by:

OSU Malheur Experiment Station/Malheur County Extension

Clint Shock, Cedric Shock, Monty Saunders, Lynn Jensen

Other Oregon State University Locations

Steve James, Kerry Locke, Ken Rykbost, Al Mosley

University of California Tulelake Field Station

Harry Carlson, Don Kirby

Most Recent Forecasts

How We Determine the Severity Indices:

How to Interpret the Severity Indices:

Late Blight Phone Numbers:

Oregon State University Late Blight Hotline, Hermiston
1 (800)-705-3377

Washington State University Late Blight Hotline
1 (800)-984-7400

No severity indices for 2004

There will be no lateblight severity indices for 2004 due to lack of funding. Thank you to the Oregon Potato Commission for their support in the past few years.

Late blight severity indices from 9/13/04:

Location	Severity Index	Updated	Information
8) Treasure Valley Malheur Experiment Station	6	1/1/00

Blightcast also distributes these severity values via electronic mail. If you would like to recieve this mailing, or have comments concerning this page, please contact:
Cedric Shock

blightcast@cropinfo.net

Or fill out and submit this form:

How to Interpret the Severity Indices:

The values are based on the predictions of Blitecast, and the adaptations we have made to the model. For example, if there is a severity index of 18 at any of the sites we suggest that you carefully follow a fungicide program.

For details of a fungicide program, please go to Oregon State University Extension Services' Plant Disease Control Guide. Fungicide programs are usually most effective if applied thoroughly and begun prior to the occurrence of late blight. Higher indexes than 18 indicate continued accumulation of late blight risk. Indexes lower than 18 suggest that late blight has less of a chance of developing and spreading.

A Severity Index of 18 means that there is the potential for potato late blight to appear within 7 - 14 days.

Please, if you have any additional questions contact us.

Determining Severity Indices:

The severity indices are determined using a model called "Blitecast". The severity values are calculated by a computer program developed at the Malheur Experiment Station.

Using the Blitecast model to predict potato late blight will help warn growers of the potential for late blight development and helps predict fungicide application. This information helps to improve disease control while reducing unnecessary fungicide sprays.

We are adapting Blitecast to help predict the potential for potato late blight in eastern Oregon and southwestern Idaho. Data such as approximate emergence date of potatoes, rainfall, relative humidity, and daily maximum and minimum temperature are all included in the model. We are obtaining this information from both local AgriMet weather stations connected by satellite and state of the art weather stations. Currently we are using a 90 % relative humidity criteria in the potato canopy and a 80 % relative humidity at the height of the weather stations. Leaf wetness data is being collected for comparison with 90 % relative humidity in the plant canopy as a prediction criteria.