Interpretation of Trap Counts and Risk Forecast

Diamondback Moth Monitoring Program

Diamondback Moth Risk for Manitoba as of June 30, 2008

Diamondback moth: Diamondback moth traps have been up for about 8 weeks in many areas, and can now be removed. Highest counts over this period were from traps near Stonewall (56), Steinbach (47), and Emerson (46). These are not alarming numbers, although it is still advised that agronomists and farmers should pay attention for diamondback moth larvae or feeding damage while scouting canola, particularly in the south Interlake and Southeast. Diamondback moth larvae have been noted feeding on canola in the southeast, but not at economical levels.

At this point in the season, information on the levels of diamondback moth is best gained by tapping plants over something where larvae can be counted, or by taking sweepnet samples where doing a general assessment of insects in the fields. Taping or shaking diamondback moth larvae off plants to do proper economic threshold assessments is necessary if levels in the net appear high.

The Role of Pheromone-Based Traps in Determining Risk of Diamondback Moth to Canola

The purpose of the pheromone-baited traps as a component of a diamondback moth monitoring program is to determine the regional risk of an outbreak in advance of the appearance of the damaging (larval) stage.

Diamondback moth does not over winter in the Canadian prairies in significant numbers, but high populations of adult moths may get blown in on winds from the south. Diamondback moth is at a higher risk of being a problem in years when high populations of adults blow in and establish early (May or early June). Thus the primary goal of this monitoring program is to establish a network of traps to determine when diamondback moth populations arrive, and in what number. This, combined with considering what the environmental conditions are like when they arrive, will determine the risk of larvae later doing significant damage to canola.

Generally, the higher the cumulative adult counts are early in the season, the greater the risk for economic damage by larvae as the season progresses. However, data is not available to correlate adult counts with levels of larvae which will follow.
The trap data is not meant to provide a risk assessment for individual fields, but a regional early warning should high moth numbers blow in during the spring.

Once larvae of diamondback moth are present in the area, it is important to be monitoring individual canola fields for feeding damage and the number of larvae, and using this data to assess the risk to crops, regardless of trap counts in the region.

For further information, contact your GO representative.