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   Wednesday, November 25, 2015

1. Brief description of Diamond back moth and larvae and lifecycle

Figure 1. Adult diamondback moth at rest.

Diamondback moth has four life states: egg, larva, pupa and adult. Crop damage is caused by the larval stage. Normally, the diamondback moth takes about 32 days to develop from egg to adult. However, the time to complete a generation may vary from 21 to 51 days depending on weather and food conditions.      

2. Do DBM over winter in Saskatchewan?

Figure 2. Diamondback moth larvae.

Yes to some degree. These tend to be isolated cases and have not been responsible for any of the large economic infestations historically.

3. What time of the season do they do damage?

Figure 3. Diamondback moth pupa.

Diamondback moth larvae have been known to cause economic damage as early as late May and have been a problem on some years later in the season debarking canola pods near harvest. It depends on when favourable winds blow moth populations from the south, usually the U.S. and Mexico.

4. What crops are at risk?

Canola crops are often most at risk due to the extent of the acreage planted annually, but all cruciferous crops, including mustard and vegetable crops such as cabbage

5. How many generations of insects are produced and how quickly?

There are usually 2 to 3 generations annually in Saskatchewan. In 2001 when the moths arrived early and had favourable climatic conditions throughout the growing season there may have been part of a fourth generation. After the first generation all life stages may be present in the field at the same time. This can cause problems with optimizing control that should be targeted at the destructive larval stage.

The time to complete a generation may vary from 21 to 51 days depending on weather and food conditions.

6. What is the present economic threshold for DBM?

Early growth stages (cotyledon and rosette) – 25 to 33 % of leaf tissue destroyed and the larvae are still feeding on the plants.

Immature and flowering fields – 100 to 150 larvae per square metre

Late flowering and podded canola – 200 to 300 larvae per square metre

7. For more information:

Diamond Back Moth Fact Sheet on this site.

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