2004 Canola Disease and Flea Beetle Survey

Janet Knodel, Area Extension Specialist - Crop Protection

Lorilie Atkinson, Research Specialist

North Central Research Extension Center, Minot

Carl Bradley, Extension Plant Pathologist, NDSU, Fargo

Art Lamey, Professor Emeritus, NDSU, Fargo

Introduction

A canola disease and flea beetle field survey was conducted in North Dakota (ND) and Minnesota (MN) in 2004.  Fields were surveyed a few days after swathing, if possible.  A total of 215 and 19 fields were surveyed in ND and MN, respectively. 

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 and part of Minnesota during 2004.  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 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 32 fields in Cavalier County, which had approximately 165,000 acres of canola in 2003.  A total of 50 plants (10 plants in 5 different sites per field) were evaluated for diseases in each field.  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

Diseases.  Results of the survey are summarized in Table 1.  This was the first year in which blackleg was recorded as penetrating or superficial lesions.  Penetrating lesions would be those that would cause economic yield reductions, whereas superficial lesions would cause no to minimal economic yield reductions.  Penetrating blackleg lesions were found on 4.6 and 0.2% of the plants evaluated in ND and MN, respectively.  Superficial blackleg lesions were found on 7.6 and 0% of the plants evaluated in ND and MN, respectively.  In 2003, plants infected with blackleg were not differentiated into superficial and penetrating lesions.  If blackleg lesions are not differentiated in the 2004 survey, then the numbers for blackleg change to 12.2 and 0.2% for ND and MN, respectively (comparable to 10.6 and 0% for ND and MN in 2003).  Sclerotinia stem rot was found on 8.2 and 6.2% of the plants evaluated in ND and MN, respectively.  Aster yellows were found on 0.6 and 5.5% of the plants in ND and MN, respectively. 

Flea Beetles.  A total of 195 fields in 22 counties of North Dakota and 9 fields in three counties of Minnesota were surveyed for flea beetles in 2004.  Flea beetle populations decreased in 2004 with an average of 9 beetles per 4 sweeps and a high of 39 beetles per 4 sweeps in ND.  In contrast, the 2003 survey averaged 52 beetles per 4 sweeps and had a high of 185 beetles per 4 sweeps in ND.  This was the first year for collecting flea beetle data in MN and populations were also low - an average of 5 beetles per 4 sweeps and high of only 7 beetles per 4 sweeps.  The cool summer weather is partially the cause for reduced pressures from flea beetles in canola this past year.  Overall, low-moderate populations of flea beetles were found throughout the traditional canola growing regions of North Dakota, such as north central and northeast (see green, blue, and yellows colors on map). 

Although the spring infestation risk is lower than previous year, NDSU Extension continues to recommend that North Dakota canola producers use either an insecticide seed treatment or a planned foliar insecticide spray(s) for protection against flea beetles in 2005.  This summer flea beetle survey is intended to provide information about potential “hot spots” of flea beetle activity in the spring of 2005.      

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.  In addition to how many flea beetles will be overwintering, weather has a big impact on their behavior and their infestation risk in spring planted canola.  For example, cool temperatures and rain in spring will delay flea beetle emergence, and suppress movements into fields and subsequent feeding activity.

Plans for 2005 are to continue the disease and flea beetle survey in swathed canola in the major canola producing counties of North Dakota, surveying approximately one field for each 5,000 acres planted in 2004. This project was partially funded by a grant from the USDA-CSREES North Central Canola Research Program.

Table 1. Results of the 2004 Canola Disease/Flea Beetle Survey in North Dakota and Minnesota.

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