NDSU

Janet J. Knodel, Area Extension Specialist/Crop Protection, North Central Research Extension Center, Minot
Holly Semler, IPM Scout, North Central Research Extension Center, Minot

Purpose and Objective:
To monitor for three insect pests of canola using pheromone traps and sticky traps in the major canola growing areas of North Dakota: Bertha armyworm (Mamestra configurata), the migratory Diamondback moth (Plutella xylostella), and crucifer flea beetle (Phyllotreta spp.). Trap data will provide growers, Ag consultants, Ag field researchers, and extension agents/specialists with an "early" warning system of when the pest become active and how many.

Summary of Results
Bertha Armyworm:
The peak flight for Bertha armyworms (BA) occurred from late June to early July. The highest trap catches were in Bottineau County near Mohall and Newburg with 703 and 699 moths per season, respectively. The second hotspot was Minot, Ward County with close to 400 moths per season, and then Burke County near FlaxtonLignite with approximately 200 moths per season. This is the first year that Bertha armyworms were captured at all trap sites. The cumulative moth capture during 2001 was 5,003 moths from 29 trap sites around North Dakota or an average of about 172.5 moths per trap site. In comparison, a cumulative total of 1,949 and 1,132 moths, and an average around 41.5 and 47.2 moths per trap site were captured in 2000 and 1999, respectively. The average number of BA moths per trap week was 24 during 2001; in contrast, the average was 7 moths per trap week during 2000. Overall, there was a dramatic threefold increase in numbers of BA populations at most trapping sites from previous years. Based on Canadian trapping guidelines, 21% (or 6 trap sites) were at the "uncertain" risk or unlikely that fields will be infested with larvae; and 79% (or 23 trap sites) at the "low" risk of larval infestation. Some field scouting for larval feeding and damage were conducted in the "hotspots" during 2001. However, very few fields had to be sprayed for BA, because larvae did not move up the plants to feed on the pods. The presence of natural controls like a nuclear polyhedrosis virus and fungi were common in fields as well. This increasing trend is alarming thou, since BA populations usually buildup several years in a row before an "outbreak" year!

Diamondback Moths:
The first flight of Diamondback moths (DBM) peaked near the end of May early June, and the second peak flight followed near mid-July. Diamondback moth migrated into North Dakota early again, as in 2000. In contrast, DBM migrated into North Dakota later in 1999 with the first peak flight near mid-June. The cumulative number of DBMs captured is 17,901 moths for 29 trap sites, or an average of 617.3 moths per site. These numbers represent a twofold plus increase over the past two years with 6,515 and 5,900 cumulative moths per season, or an average of 271.5 and 125.5 moths per trap site for 2000 and 1999, respectively. The average number of moths per trap week was 78 during 2001; however, the average was about one-half that during 2000 with 40 moths per trap week. Field scouting is usually necessary when more than 100 DBMs are captured per trap week for several weeks prior to bloom to early bud development. Unfortunately, some canola fields suffered yield losses, because they were not sprayed, or the proper spray timing for DBM control was missed. Fields that were damaged were in the areas with high trap captures from Mountrail, Ward, McHenry, northward to Burke County. This year, the first record of DBM larvae destroying a canola field in the seedling stage was also observed near Velva. The site with the highest trap count was Mountrail County near Parshall with 1,876 total moths, and then Thief River Falls, Minnesota with 1,515 total moths. Diamondback moths were captured at all of the trap sites during 2001. The presence of natural controls like a nuclear polyhedrosis virus and fungi were common in field.

Crucifer Flea Beetles:
During 2001, the crucifer flea beetle (FB) activity started late, close to late-May, which was later than the year 2000. A total of 6,734 FBs were captured on sticky yellow traps from 19 different trap sites with an average trap catch of 73 per trap week. The highest average trap catch was 515 beetles per trap week in Langdon, 274 per trap week in Minot, and 192 per trap week in Carrington. There were two major peaks with the major activity in late May, and again in late June. Minot had the highest cumulative trap catch with 1,915 total FBs, then Langdon with 1,546 total FBs, Carrington with 958 total FBs, and Watford City with 625 total FBs. The FB trap catches were lower at other sites partly because the monitoring effort was not as continuous throughout the field season, and traps may have been placed in commercial seed treated canola fields. Traps were also monitored longer (end of July) at the research extension centers. Flea beetle pressure was generally lower from regions where canola has been grown for only a few years, such as Southwest. However, it was interesting to note the 8fold increase in the western region of North Dakota for McKenzie County. The duration of the feeding period was typical approximately 1 to 1.5 months long. The majority of the canola crop was planted during early-mid May in the North Dakota, which provided opportune time for the emerging flea beetles to infest. However, the weather conditions in 2001 were not conducive to early flea beetle feeding due to dry conditions in the North Central Region, and the statewide windy field conditions. Unfortunately, some canola fields located in heavy FB "hotspots" had to be rescued with one or more applications of a foliar insecticide regardless of whether the seed was treated or not.

Canola Insect Trapping Network Web Site:
Data for the Canola Insect Trapping Network was updated weekly on the NC Research Extension Center’s webpage under "Pest Notes" during the 2001 field season:
http://www.ag.ndsu.nodak.edu/minot/pest/pn.htm
Please see the website for more information from the different field sites.

Acknowledgements:
Authors would like to thank the trap cooperators, which included County Extension Agents, Area Extension Specialists, Crop Consultants in North Dakota and Minnesota for making this a successful network.