Manitoba Agriculture, Food and Rural Initiatives

Trap Assembly and Monitoring Protocol for Bertha Armyworm

Purpose of Monitoring Program

Bertha armyworms can be serious pests of canola in Manitoba. It is the larval stage that is damaging to the plants, however the adult stage appears before the larvae are present. This provides an opportunity to assess in advance the risk of a potential outbreak.

The pheromones used by female bertha armyworm moths to attract males are known and are synthesized for use in monitoring programs. These synthetic pheromone lures are very effective at attracting male moths to traps, which have been designed to capture and kill the moths. This system provides a relatively simple and effective method of monitoring and predicting in advance outbreaks of the damaging larval stage of bertha armyworm.

The purpose of this monitoring program is to determine the regional risk of an outbreak in advance of the appearance of the damaging (larval) stage. This gives farmers, farm production advisors, agronomists, chemical dealers, and others involved in pest management some advanced warning of a potential outbreak, and enables them to place proper emphasis on monitoring for the larvae. It also provides time for agriculture retailers to have the appropriate insecticides in place.

At no time should a decision to use insecticides to control bertha armyworm be made based only on information from the traps for adults of this insect. Such decisions need to be made after later sampling for the damaging (larval) stages of bertha armyworm and determining if the levels of larvae present in the field are above the economic threshold. Weather can affect the success of mating and laying eggs, and many mortality factors could reduce the numbers of eggs and larvae before they develop to the damaging stage.

When to Monitor

Bertha armyworm traps are normally placed in canola fields during the first week in June with the first moth counts being recorded the second week in June. Traps should be checked and the number of moths counted once per week. Traps can be removed after counts for the last week of July.
 

Where to Put the Traps

Traps should be located two meters in from the field edge and away from any existing shelterbelts. When more than one trap for bertha armyworm is placed in a field, traps should be located a minimum of 110 meters apart. If diamondback moth and bertha armyworm traps are both located in the same field, a distance of at least 50 meters between the two trap types is recommended.

The site selected for the traps should be representative of the surrounding area, and at least 1/4 mile from the nearest farmyard so that the lights do not compete with trap attraction.

Tips for Setting Up the Traps

1. Place a vaportape insecticidal strip inside the bucket of the trap so the moths are killed when they fly in (Figure 1).

Figure 1 Vaportape insecticidal strip (red) in trap

Figure 2 Trap components

2. Secure the funnel and lid in place as shown in Figure 2. Place the lure basket into the lid of the trap.

3. Place the lure (rubber stopper containing pheromone) into the lure basket, and place the cap on the lure basket. Do not handle the rubber stopper with your hands. Oil from your skin can lessen the lures' effectiveness. Transfer lures while handling only the plastic tie attached to the rubber stopper, or use rubber or latex gloves or tweezers to handle lures.

4. Mount the traps about three feet off the ground on a sturdy stake. The trap can either be hung by a wire hangar from a horizontal post (Figure 3a), or it can be secured by placing a metal spike secured to the bottom of the trap into a hollow metal pole that has been hammered into the ground (Figure 3b).

For further information, contact your GO representative.