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Diamondback Moth
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 | Diamondback moth larva Photo courtesy the Canola Council of Canada |
Description
Diamondback Moth is a periodic pest of canola across the prairies. The adult moths get their name from the diamond-shape markings that are formed when their wings are folded at rest. The moths have a narrow appearance and are about 1 cm or ½ inch long. They are gray or brownish with white marks on the front margins of the forewings. Infestation of Diamondback moths cannot be predicted based on the previous year's population. The moths are weak flyers that don't survive winter in Canada, but they can appear in large numbers when winds from the south carry them from the United States in early May.
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| Adult Moth Photo courtesy Agriculture and Agri-Food Canada |
Larvae Photo courtesy the Canola Council of Canada |
Life History
Females tend to deposit eggs (about 160) in the depressions created by leaf veins or where the leaf petioles clasp the stem. Small green larvae hatch within a few days and enter the leaves to feed on, or "mine", the internal tissue. After feeding inside the leaf for about a week, the larvae move to the outside of the leaf. The smooth, pale yellowish-green larvae commonly cut holes or feed on the outer tissue of leaves or seed pods. When disturbed, the larvae wiggle violently and drop from the plant on a fine silken thread. Larvae feed for 10 to 30 days, depending upon food supply and temperature, to reach a mature length of about 12mm. Pupation takes place in delicate white, open mesh cocoons attached to the leaves, stem and seedpods of the host plant. Initially, the pupae are light green but as they mature, they become brown as the adult moth becomes visible through the cocoon. Depending on environmental conditions, the pupal stage lasts from 5 to 15 days.Damage
Crop damage is sometimes first seen on plants growing on ridges and knolls in the field. When larvae are small, damage is seen as small irregular holes in the leaves. If the larvae are numerous, they may eat an entire leaf, leaving only the veins. When the crop matures, larvae feed on the outer green tissue of the pods, leaving plants with a whitened appearance when viewed from a distance.Economic Threshold
Monitor larvae by removing the plants in an area measuring 1/10 of a square meter (about 1 square foot, 12 inches square). Beat these plants on a clean surface and count the number of larvae dislodged. Repeat this procedure with plants from at least five different locations in the field. Multiply the average count by ten to obtain the population per square meter. In canola the economic threshold for Diamondback moth is above 100-150 larvae/sq m at early flowering OR 200-300 larvae/sq m at the pod stage. These numbers indicate significant damage may be expected and control should be considered. If the crop has large, healthy plants with lots of leaves and pods are maturing quickly, a higher larval density may be tolerated without damage to yields.Forecast Maps
For more information, contact:
Kerry Clark, Crop Protection Specialist
BC Ministry of Agriculture and Lands
1201 103rd Avenue
Dawson Creek BC V1G 4J2
Tel. 250 784-2559
Fax 250 784 2299
Toll Free: 1-877-772-2200
Email: Kerry.Clark@gov.bc.ca
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