2003 ND Wheat Disease Survey

2003 North Dakota Wheat Disease Survey

Marcia McMullen, Extension Plant Pathologist, North Dakota State University, Fargo, ND
Roger Ashley, Area Extension Agronomist, Dickinson Research Extension Center, Dickinson, ND
Greg Endres, Area Extension Agronomist, Carrington Research Extension Center, Carrington, ND
Phil Glogoza, Extension Entomologist, North Dakota State University, Fargo, ND
Terry Gregoire, Area Extension Agronomist, Devils Lake Area Office, Devils Lake, ND
Jan Knodel, Area Crop Protection Specialist, North Central Research Extension Center, Minot, ND

Introduction:

The purpose of the wheat disease survey is to detect the presence and severity of leaf and head diseases that are common in North Dakota and to verify the absence of diseases that might be of export concern. Survey information is provided on a timely basis to ND producers to assist them in disease management decisions. The survey information also is used to estimate losses due to disease and to help validate disease forecasting models.

Materials and Methods:

Field scouts surveyed for leaf and head diseases of winter wheat, hard red spring wheat, and durum wheat. Fields were surveyed in all 53 counties, with approximately one field per 7500 acres per county as the goal for survey coverage. Survey scouts operated out of the Dickinson Research Extension Center, the North Central Research Extension Center, the Carrington Research Extension Center, the Devils Lake Area Extension Office, and the Fargo Experiment Station. Each scout had a designated territory within his/her field scouting area.

Fields were surveyed on a representative route, with approximately one field per every 10 miles. Data for each field was recorded on handheld iPAQ computers in an Excel spreadsheet. Data for each field included: date, county, field location in GPS units and legal description, previous crop (based on residue present or volunteers), crop, growth stage, grasshopper, aphid, and cereal leaf beetle numbers, and incidence and severity of fungal, viral, and bacterial diseases of leaves and grain heads. Crops were surveyed from the two-leaf stage through kernel hard dough stage. In each field, the field scout examined five locations along a W pattern, 10 main stems per location, for a total of 50 plants. Incidence was recorded as % of main stems showing symptoms, while severity was based on % leaf or head area showing symptoms. Prevalence was determined as % of fields showing symptoms of a particular disease.

Results:

A total of 1278 wheat fields were surveyed in 2003 across all ND counties. The numbers represented approximately one field surveyed per 7000 wheat acres/county. Surveys began on May 25 and continued through August 13. The August date surveys were primarily in the northeast and north central crop reporting districts where crops had been planted later.

Wheat leaf rust (Puccinia triticina) was found in 284 or 22.2% of all fields surveyed. Leaf rust was found in all but nine counties, and primarily absent in the southwest and far northwest counties. The average wheat leaf rust severity across all fields was 6.2%, and the average severity within counties ranged from 0 to 18.6%. Highest severities in individual fields were found in Sargent county and in later maturing fields in counties in the northeast and north central crop reporting districts (Table 1).

Tan Spot: Tan spot (Pyrenophora tritici-repentis) was the most frequently occurring disease observed, found in 59.9% of all fields surveyed. The statewide average severity of the disease was 4.7% (Table 1). The highest average severity was found in counties in the central crop reporting district (Table 1).

Table 1. Average severity of leaf rust, tan spot, Septoria and Fusarium head blight (scab) in surveyed wheat fields per crop reporting district, ND 2003

	LEAF RUST	TAN SPOT	SEPTORIA SPP.	FUSARIUM (SCAB)
Crop Reporting District	Avg. % Leaf Severity	Avg. % Leaf Severity	Avg. % Leaf Severity	Avg. % Field Severity
C	8.7	10	7	1.1
EC	5.6	1.2	20.5	0.4
NC	7.6	3.7	7.4	3.2
NE	7.3	4.2	6.4	2.7
NW	6.7	4.2	7.2	0.03
SC	5.4	5.3	1.2	0
SW	0.1	4.3	1.3	0
SE	9.3	5	11.7	1.0
WC	5.4	4.7	5.4	0
State Avg.	6.2	4.7	7.4	0.9

Septoria Leaf Disease Complex: The Septoria leaf disease complex (Septoria tritici, Stagonospora nodorum, Stagonosopora avenae f. sp. triticea) was observed in fewer fields than tan spot (24.7% vs 59.9%), but the statewide average severity was higher (7.4% vs 4.7% for tan spot) (Table 1). The highest average severities of Septoria were observed in the east central district. Septoria was primarily observed in fields surveyed after flag leaf emergence. The head infection of Septoria fungi, glume blotch, was observed in 22.7% of post-flowering fields, all in the east central, southeast or northeast counties.

Fusarium head blight (scab): Fusarium head blight (scab) occurrence and severity were the lowest recorded in disease surveys since the 1993 epidemic. Although scab was observed at some level in 27.6 % of post-flowering fields surveyed (Figure 1 = > Zadoks growth stage 70 = post flowering), scab was not observed in 26 counties (Figure 1). The average field severity of scab across all fields was 0.9% (Table 1). Fields with the most frequent observations and highest severities were in counties in the northeast and north central crop reporting districts (Figure 1), where fields received more rainfall during flowering and grain fill.

Figure 1. Fusarium head blight (scab) in wheat, ND 2003

Other Diseases Observed:

Stripe rust: Stripe rust (Puccinia striiformis) was observed in 34 fields across the state, primarily in counties on a diagonal line running from the southeast corner to the northcentral region. The disease was observed in 15 counties, with the most frequent observations (8) in Mountrail county. Severity was generally less than 2%. The occurrence of stripe rust was unusual for the state, as it is a disease generally associated with very cool, wet environments. Cool, wet weather in May and June favored infection. This rust developed in southern plains states prior to moving into ND on prevailing winds.

Spot blotch: Spot blotch (Cochliobolus sativus) was observed on leaves of wheat in 11.2% of all wheat fields surveyed, primarily in the southwest counties. This leaf spot disease is generally favored by warm, drier conditions than other common fungal leaf spot diseases of wheat.

Bacterial leaf blight (stripe) and Black Chaff: Bacterial leaf blight was observed in 3% of fields surveyed, and black chaff, the bacterial head infection, was observed in 1% of fields surveyed after heading. The fields with symptoms of bacterial infection were all located in the northeast.

Ergot: Ergot infections were only observed in 2.7% of the post-flowering fields surveyed, all in the Northeast.

Loose smut: Of the post-headed fields surveyed, 37.3% had symptoms of loose smut. The average infection incidence of infection in fields showing symptoms was 5.4%, while the range of incidence was

2% to 30%. The highest levels of loose smut were found in southwest counties, but loose smut also was common in the east.

Barley Yellow Dwarf Virus (BYDV): BYDV was observed in 7% of the fields surveyed. The predominate location of symptomatic fields was in the northeast, an area where grain aphid populations also were very high. Grain aphids transmit this virus.

Diseases Not Observed in Survey: The following diseases were surveyed for and NOT found in 2003:

Wheat streak mosaic virus; stem rust; flag smut; dwarf bunt; and Cephalosporium stripe.

Discussion: Early rains in May and June favored development of tan spot on tillering to jointing wheat. Septoria infections developed primarily after boot stage of development. Economic levels of these two diseases precipitated use of fungicides in many areas. Leaf rust infections were detected early (May 28 in Logan and Sargent counties). Leaf rust was severe in some fields along the SD border and in late planted spring grains along the northern counties. The dry conditions in many areas limited diseases, most noticeably Fusarium head blight or scab. The high percentage of fields showing loose smut infection after heading and the high percentage of infected heads in some fields indicates an economic damage from this disease is occurring in many ND wheat fields. The occurrence of stripe rust was more widespread than seen before.

Acknowledgements: The authors wish to thank the ND Dept. of Agriculture, the ND SBARE Wheat Research Granting Committee, and the ND Wheat Commission for financial support of this survey effort on wheat. Many thanks to the field scouts of 2003: Lorilie Atkinson, Nathan Carlson, Cindy Leisy, Tammy Link, Patrick Metzger, Chris Stroklund, Cody VanderBusch, and Nikki Zahradka.