Thursday, 21 June 2018

Diamondback moth (Jun 21, 2018; Wk 07)

Diamondback moth (Plutellidae: Plutella xylostella) - Once the diamondback moth is present in the area, it is important to monitor individual canola fields for larvae.  Warm growing conditions can quickly translate into multiple generations in a very short period!


Remove the plants in an area measuring 0.1 m² (about 12" square), beat them on to a clean surface and count the number of larvae (Fig. 1) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.

Figure 1. Diamondback larva measuring ~8mm long.
Note brown head capsule and forked appearance of prolegs on posterior.

Figure 2. Diamondback moth pupa within silken cocoon.

Economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1  (approximately 2-3 larvae per plant).  Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1  (approximately 1-2 larvae per plant).

Figure 3. Diamondback moth.

Across the prairies, provincial staffs coordinate diamondback pheromone trapping during the growing season.  Every spring, the early arrival of diamondback moths (Fig. 3) is monitored through the tracking of high level air masses that originate from the south of North America and arrive across the Canadian prairies. Additionally, pheromone traps are deployed to intercept the initial moths.  Cumulative male moth counts occurring over a 6-7 week period of trapping are used to estimate relative risk for the growing season.  Vast networks of cooperators across Manitoba, Saskatchewan, Alberta, and the BC Peace work with their provincial entomologists to generate the following in-season results: 

● Counts are summarized by Saskatchewan Agriculture (updated June 15, 2018, by J. Tansey):

● Manitoba Agriculture generally reports low DBM counts so far but review the specifics by region within the latest Insect and Disease Update (June 6, 2018).  

● Alberta Agriculture and Forestry has a live 2018 map reporting Diamondback moth pheromone trap interceptions.  A copy of the map (retrieved June 21, 2018) is below for reference.

Biological and monitoring information for DBM is posted by Manitoba AgricultureSaskatchewan AgricultureAlberta Agriculture and Forestry, and the Prairie Pest Monitoring Network.  

More information about Diamondback moths can be found by accessing the pages from the new "Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide".  View ONLY the Diamondback moth page but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.