NDSU Crop and Pest Report
Plant Pathology

ISSUE 4   May 27, 2004


The NDSU Small Grain Disease Forecasting web site is now ready for the 2004 season. The web address is:


Toll free phone information also is available at 1-888-248-7382 or (231-6601 in Fargo calling area). Dr. Shaukat Ali of the NDSU Plant Pathology Department will be maintaining this site.

This web site provides information on risk of tan spot, Septoria blotch, leaf rust and Fusarium head blight (FHB = scab) for the 50 ND, 9 MN and 1 SD NDAWN locations. A viewer will be instructed to follow these steps:

  1. Click on the nearest North Dakota Ag Weather Network (NDAWN) station location
  2. Choose appropriate growth stage: flagging, boot, heading, flowering, early milk (note: only heading and beyond growth stages will provide information of Fusarium head blight risk)
  3. Click on "Get Forecast".

For leaf diseases, the information provided for each NDAWN location includes a table that indicates if weather conditions the previous 13 days were favorable for infection for fungi that cause tan spot, Septoria and leaf rust. If 6-8 infections periods occurred, a fungicide should be considered.

For FHB (scab), a table is provided indicating the risk of FHB infection for the previous 13 days for that location, plus a link is provided to a map indicating risk across the whole state. In the map, risks are color coded: red = high risk; yellow = intermediate risk; and green = low risk.

The NDSU FHB risk table and map are derived from a revised model developed at Penn State and Ohio State. The developers of the models used ND and SD disease and weather data to validate the model for spring wheat. The revised 2004 model has a improved prediction accuracy over the previous model. The weather variables of temperature, duration of rainfall, and relative humidity are the components of the model. The weather data is taken daily from the NDAWN weather stations in the region.

The model estimates the risk of a scab epidemic with greater than 10% severity using weather variables observed seven days prior to flowering. Weather during this pre-flowering time period influences the reproduction of the fungus that causes head scab. Testing of these pre-flowering models indicate that prediction accuracy is near 80%

US Wheat and Barley Scab Initiative FHB Model:
Another FHB risk map is available through the US Wheat and Barley Scab Initiative. The model components of this risk map are the same as for the ND forecasting web site, but the weather data is not coming from NDAWN stations. Weather data for this risk prediction map are primarily from "calculated" weather rather than real time weather. The following information is taken from the web site listed below:

"The colored maps are produced using a source of weather information known as the Rapid Update Cycle (RUC) created by the National Weather Service. The RUC system combines multiple sources of weather information to generate observations of temperature and dew point temperature (converted to relative humidity (RH) for our purposes) on a 20km grid throughout a region. The observations of temperature and RH are combined with Doppler radar estimates of rain to produce maps of disease risk with a 20km resolution. In addition to the RUC data the disease forecasting system also uses weather stations, represented as "dots" within the map, throughout the region to provide temperature, RH and rain data to present on the graphs., plus from a few National Weather locations" For ND, 10 National Weather locations are indicated. The FHB risk map for this site may be viewed on the Internet, at the following web address:


Click on the link to the risk map tool, and follow the instructions to get to spring wheat for ND.

In summary, both sites are using the same model but different weather data. Both sites are using the previous 7 day weather variables to predict FHB risk. Neither model is predicting risk on future weather events. Individual farmers and crop advisors will still have to look at the weather forecast to determine if weather will continue to be favorable for disease or if it will suddenly shift to hot and dry conditions, unfavorable for FHB.

Currently, the risk map based on the NDAWN weather stations and the US Wheat and Barley Scab Initiative risk map are both showing low risk for FHB in ND. 2004 will provide an opportunity to assess the US Wheat and Barley Scab Initiative model using estimated weather data, compared to the NDSU risk map using real time NDAWN weather data.



In the last two years, FHB spores were collected with spore samplers at several locations across ND, including at some Research Extension Centers. This year the spore collecting and counting will be discontinued.

Spore counts were very labor intensive, and information on spore numbers were frequently delayed and often did not directly correlate to real time weather or disease events. A research study on FHB spore counts and distribution will be continued at NDSU in Fargo to further examine relationships between spore development, populations, environment, and disease risk.



Temperatures may have warmed up again by the time this Crop and Pest Report gets published, but temperatures last week and during the early parts of the week of May 24 were too cold for diseases and alsofor early season fungicide application.

If fungicide/herbicide tank mixes were applied when temperatures dipped into the 30 or 20 degree F at night, some leaf burn may have occurred. Recent rains and warmer temperatures may likely increase the risk of tan spot, but please donít mix herbicides and fungicides and apply when night time temperatures are dipping into the 30s or below. Tender, stressed wheat plants are subject to increased injury under these cold temperatures.

Marcia McMullen
Extension Plant Pathologist



Rhizoctonia stem canker, caused by the fungus Rhizoctonia solani, is showing up in potato fields, and symptoms are becoming especially severe in those fields that were not treated with an in-furrow application of Quadris, Amistar, or Moncut. The cool, wet weather that we have been experiencing has been slowing the growth of the potato plants and favoring disease development. Symptoms of Rhizoctonia canker on stems and stolons appear as brown to black sunken lesions. If conditions are favorable, these lesions can continue to expand and cause stem girdling.

Rhizoctonia canker of potato
(photo by N. Gudmestad)

Management practices that can minimize Rhizoctonia canker include crop rotation (at least 3 years), delaying planting for warmer soils, and in-furrow fungicide applications of either Amistar, Quadris, or Moncut. For more information on Rhizoctonia canker and other regional potato diseases visit the NDSU Potato Disease Website at:


Carl Bradley
Extension Plant Pathologist



The Plant Pathology Department will again be providing the potato late blight hotline service at no charge to the potato industry of North Dakota and western Minnesota in 2004. This will be the tenth year that this service has been provided, and is sponsored by Syngenta Crop Protection and Amistar fungicide. The hotline uses local weather data collected from weather stations throughout our area to forecast the occurrence and spread of late blight in fourteen non-irrigated and nine irrigated production areas in ND and western MN. The data is processed by the North Dakota Agricultural Weather Network (NDAWN) and analyzed by a computer program (WISDOM) to forecast when conditions are favorable for late blight to occur.

This information is used by plant pathologists Gary Secor and Neil Gudmestad to make late blight management and fungicide recommendations. The recommendations are made Monday, Wednesday and Friday of each week during the growing season. The first late blight hotline will be Wednesday June 2nd, and the hotline will continue through mid September depending on disease pressure. The hotline will also be used to confirm late blight infection and serve as clearing house for national late blight information. The hotline also provides cumulative P-values for early blight disease forecasting and management recommendations. In addition, it serves to alert growers of other disease and pests, as well as posting messages of importance including potato field day schedules.

The hotline recommendations can be accessed by phone or website. The toll free phone number is 1.888.482.7286. The website is:


In addition, Dr. John Enz of the Soil Science Department, has produced a website that uses colored maps of ND to pictorially illustrate the late blight severity values (both two day and seasonal), favorable day values and P-day values for early blight throughout ND. That site is:


Growers and scouts are encouraged to send suspect late blight samples to us for identification and genotype identification. It is important to receive samples as quickly as possible after collection. Leaf samples should be placed in an slightly inflated zip-lock plastic bag without a wet towel and sent to:

Gary Secor
Plant Pathology
Walster Hall 306
North Dakota State University
Fargo, ND 58105

Gary Secor
Plant Pathologist


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