Canola IPM Survey for Diseases and Flea Beetles

 Janet J. Knodel¹ and Art Lamey^2
1Crop Protection Extension Specialist and ²Professor Emeritus
¹Minot and ²Fargo
North Dakota State University

Introduction

A canola survey for diseases was conducted in North Dakota and Minnesota during 2003.  The disease survey included all major canola regions in the two states. 

Flea beetles, principally the crucifer flea beetle, Phyllotreta cruciferae (Goeze), are the most economically important insect pest of canola in North Dakota and Minnesota.  Information on the incidence, distribution and severity of flea beetles was collected on canola grown throughout North Dakota during 2003.  The population level of summer flea beetles is used for forecasting the 2004 spring infestation risk, and for developing appropriate grower education programs for areas with moderate-high flea beetle risk. 

Several IPM scouts in North Dakota, as well as county extension agents in northeastern North Dakota and northwestern Minnesota were involved in conducting these cooperative surveys. 

Materials and Methods

The canola survey was conducted when the crop was in the swath.  Approximately one field was surveyed for each 5,000 acres of canola planted the previous season in each county.  The greatest number of fields surveyed was 41 fields in Cavalier County, which had approximately 200,000 acres of canola in 2002.  In each surveyed field, the stubble was examined for Sclerotinia stem rot and blackleg, the pods were examined for Alternaria black spot and the swath was examined for aster yellows.  For crucifer flea beetle, county extension agents and IPM scouts swept freshly swathed canola stubble, usually during late July into August, using a 15-inch sweep net.  The number of flea beetles per 4 sweeps was recorded at 5 locations for a total of 20 sweeps per field. 

Results and Discussion

The disease survey included all major canola regions in the two states.  There were 260 fields surveyed in 27 counties as follows:  249 fields in 25 counties in North Dakota and 11 fields in 2 counties in Minnesota.  The survey included 90 fields in 4 counties in northeastern North Dakota, 54 fields in 5 counties in north central North Dakota, 53 fields in 5 counties in northwestern North Dakota, 18 fields in 5 counties in central North Dakota, 18 fields in 1 county in west central North Dakota, 16 fields in 5 counties in southwestern North Dakota and 11 fields in 2 counties in northwestern Minnesota.

Although Sclerotinia stem rot has been the most frequent disease problem in both states, the incidence (percent infected plants) was only 4% in North Dakota in 2003, the lowest in 12 years of survey in the state.  Incidence in Minnesota was 12.5%, the second lowest in 8 years of survey.  The only counties with high incidences of Sclerotinia were Roseau, MN; with 17.3%, Pierce, ND, with 11.8%; and Cavalier, ND, with 9.6% (see map).

Historically, blackleg has not been a major disease problem since 1991, but in 2003, the blackleg incidence in North Dakota was 10.6% due to extremely high levels in four northeast and north central counties:  35.8 % in Pierce, 29.8% in Towner, 27.0% in Cavalier and 11.7% in Ramsey (see map).  The survey data corroborated reports of blackleg by producers and seed dealers.  Following these findings the Northern Canola Growers Association convened a group of industry and NDSU extension personnel and developed a strategy for blackleg, which is available on a CD ROM for all producers.  Very low levels of infection were observed for Alternaria black spot and aster yellows. 

Results of the flea beetle survey are summarized in Table 1 and map.  A total of 156 fields in 22 counties of North Dakota were surveyed for flea beetles.  High risk areas that are indicated by high number of flea beetles (75-100+ beetles per 4 sweeps) in the swathed canola include the following regions and counties: 

North Central:  Benson, Bottineau

Northwest:  Ward, Mountrail, Renville

Central:  Foster, Sheridan

West Central:  McLean, Dunn (only 1 field sampled)

South Central:  Grant (only 1 field sampled)

Southwest:  Hettinger

Overall, high populations of flea beetles were found throughout the traditional canola growing regions of North Dakota (north central, northwest).  These results also indicate that flea beetles have already become an economically important insect pest in the newer canola production areas, like the south central and southwest.  Moderate risk areas include primarily the Northeast and Central Regions of North Dakota.  Overall, canola is under moderate-high risk from flea beetle pressures in most of the state.  As a result, NDSU Extension recommends that North Dakota canola producers use either an insecticide seed treatment or a planned foliar insecticide spray(s) for protection against flea beetles in 2004.  This summer flea beetle survey is intended to provide information about potential “hot spots” of flea beetle activity in spring 2004.  Forecasting “Pest Alerts” are an important tool of Integrated Pest Management, and producers need to be aware of risk factors; such as, when and how many beetles will be emerging from their overwintering sites and moving into fields.

Plans for 2004 are to continue the disease and flea beetle survey in swathed canola in the major canola producing counties of North Dakota and Minnesota, again surveying approximately one field for each 5,000 acres planted in 2003.   

Last Updated: Tuesday, July 05, 2005 10:26:36 AM
Published by North Dakota State University