NDSU Crop and Pest Report
Plant Pathology


ISSUE 6  June 5, 2003

POTATO DISEASE FAX SERVICE HAS BEGUN

The Dow AgroSciences late blight forecast fax service began June 1. The service provides forecast maps for late blight and will be faxed 2-3 times per week (depending on disease pressure) until mid-September. The service is sponsored by Dow AgroSciences and is provided through cooperation with Drs. Gary Secor and Neil Gudmestad of the NDSU Plant Pathology Department and Dr. John Enz, NDSU climatologist. The service distributes late blight forecast maps from the NDAWN late blight forecasting website, which became operational last year. The maps are generated using weather information from NDAWN stations across the state. The fax service is designed to distribute information quickly and when computer access in not available or convenient. To subscribe to the service, please call the Dow Agrosciences Customer Information Center at: 1-800-258-3033.

 

SOYBEANS WITH "BALD HEADS"

Soybean seeds that had been sitting in the cool, wet soil for an extended period of time are now starting to pop out of the ground. Some of the emerging seedlings may be showing "bald head" symptoms (Figure 1). A "bald head" symptom appears when the seedling’s growing point has been killed or damaged. The soybean pathogen, Pythium, can attack and damage the growing point of soybean seeds and seedlings as they germinate in cool, wet soil conditions. Plants exhibiting "bald head" symptoms will probably not die, but may produce a plant with two stems (a forked plant). Pythium seedling blight can be managed with the use of a seed treatment that contains either Apron XL (mefenoxam) or Allegiance (metalaxyl).

Fig. 1. "Bald head" symptom caused by Pythium. Photo courtesy Mississippi State University.

Carl A. Bradley
Extension Plant Pathologist
cbradley@ndsuext.nodak.edu

 

IPM SURVEY - DISEASES OBSERVED IN WEEK 1

The IPM field scouts examined 104 wheat fields, 11 barley and 5 canola fields last week (ending May 30) for insects and diseases.

Tan spot infections were observed in 54% of the wheat fields surveyed. Incidence of plants infected per field was as high as 100% in some wheat on wheat fields. Tan spot was also observed in fields of wheat planted into soybean ground, but incidence was low. Overall severity of tan spot ranged from 1-15%, with the highest severity in a winter wheat field.

Wheat leaf rust was observed on spring wheat in three counties by May 30th, in Logan, Sargent and Grand Forks counties. This is an earlier than normal detection of wheat leaf rust in the state. Incidence of plants infected was low, from 2 to 6%, and severity was at a trace amount.

Weekly maps of IPM survey results, including field locations, crop growth stage and disease incidence and severity can be found on the Web, at the ND IPM web site:

http://www.ag.ndsu.nodak.edu/aginfo/ndipm

Jerry Schneider, a teacher at Fargo North High School, and former IPM survey scout, is coordinating collection and posting of IPM survey results.

 

CEREAL RUST UPDATE

Trace amounts of wheat leaf rust have been observed now in North Dakota (see above). The June 3 edition of the Cereal Rust Bulletin, published by the USDA Cereal Disease Lab in St. Paul, indicates that wheat leaf rust was severe in fields of susceptible cultivars from central Kansas to west central Missouri. In south central Kansas, 60% severities were found on flag leaves of Jagger winter wheat and 10% severities were observed on Jagger in northeast Kansas. They state that "the southern leaf rust sites will provide leaf rust inoculum for the northern wheat growing area". Our late planted, susceptible cultivars will be at the greatest risk.

Stripe rust has also been observed at severe levels on wheat leaves in Kansas fields. Traces of stripe rust also were found in South Dakota winter wheat plots. We have not observed any stripe rust yet in North Dakota.

The Cereal Rust Bulletin reports only trace levels of oat stem rust, crown rust, and barley leaf rust have been observed, either in southern states or California. It is too early to know how extensively these rusts will develop.

 

SMALL GRAIN DISEASE  FORECASTING MODELS

The NDSU Small Grain Disease forecasting Model Web site is up and running for 2003. The Web site is:

http://www.ag.ndsu.nodak.edu/cropdisease/cropdisease.htm

Automated computer models for leaf diseases and Fusarium head blight (scab) are now activated. Check the list of towns for NDAWN weather station locations that are new to this Web site this year. Sampling of Fusarium spores in the southern part of the valley region will begin in about two weeks. Sampling for Fusarium spores in the northern part of the region will end around August 3. Dr. Shaukat Ali of the NDSU Plant Pathology Department is in charge of maintaining the system and coordinating spore sampling.

The forecasting models are available for tan spot of wheat, Septoria (Stagonospora) blotch, leaf rust and Fusarium head blight (FHB = scab). A visitor to the site must pick a location of the nearest NDAWN station and a growth stage. Then information on the favorability of infection for these diseases is given for the past 13 days. Not surprisingly, many sites have had favorable weather for tan spot infection. For example, the

Carrington site data for June 3:
Yes = infection likely; No = infection unlikely

Model

6/2

6/1

5/31

5/29

5/28

Tan spot

Yes

Yes

No

No

Yes

Sep. Blotch

No

No

No

No

No

Leaf rust

No

No

No

No

No

To get the Fusarium head blight (FHB) forecast, the flowering growth stage must be selected. Information is then provided from two models. Model I will provide risk at flowering, the time at which a fungicide decision must be made.

Example of FHB (scab) data from Carrington on 6/3: % risk of FHB

Model

6/2

6/1

5/31

5/29

5/28

Scab risk Model 1

5%

4%

5%

4%

3%

Obviously, the risk of scab is very low now, even if the crop was in the flowering stage, which it is not. Model II provides information on risk following flowering, indicating potential impact on market grade if fungicide spraying was not used on a susceptible cultivar. Growers will need to be paying attention to Model I for their fungicide decisions. The above table information is also presented graphically in a map format. Click on the Model I link and the map graphic indicating risk levels will be available.

Marcia McMullen
Extension Plant Pathologist
mmcmulle@ndsuext.nodak.edu


NDSU Crop and Pest ReportTop of PageTable of ContentsPrevious pageNext page