Diamondback moth

Constraint - Diamondback moth

Description

• DBM caterpillars are pale yellowish green and tapered at each end of their body

• They grow to about 12 mm long and often wriggle rapidly when disturbed

• Moths are about 10 mm long and grey-brown in colour with a characteristic whitish strip down the back, which resembles diamond patterns

• DBM is the most destructive insect pest of brassicas worldwide

Symptoms

• Damage occurs in spring and summer

• Oval cream coloured eggs presnt on stems and the undersides of leaves

• Feeding damage causes clear membranous windows in leaves

• Larvae also feed on pods

Damage

• Seedlings may be completely eaten

• Severe defoliation and pod grazing of mature plants may cause greatly reduced seed set

• In extreme cases, the whole crop has been ploughed under and no yield has been achieved

Control

Management of diamondback moth requires an integrated approach as it is difficult to get insecticide contact with the diamondback caterpillar due to its feeding sites, and it has a marked ability to develop resistance to insecticides. When pest pressure is low, predators and wasp parasitoids of this pest can provide an acceptable level of control. Use of the bacterial insecticide, Bacillus thuringiensis, can also be effective when populations are low, and is non-toxic to predators. Using chemicals wisely by saving insecticides for high pest populations, or when larvae are less than 5 mm long to ensure a good kill rate can also help decrease insecticide resistance development. As a last resort, ploughing in crop residues or heavily infested crops promptly may prevent the spread of populations to as yet unaffected crops.

Links and Resources

CESAR - Pestfacts. Diamondback moth Information on distribution, insecticide resistance, appearance, sampling and monitoring, and winter canola considerations for Diamondback moth. Published 2012.

DAFWA - Identification of pests of canola. Diamondback moth Pages 24-25. Information on description, lifecycle, damage, and control. Published 2005.

DEPI VIC - Diamondback moth Introduction, description, biology, damage, and control. Published 1996, updated 2013.

GRDC - Best Practice Management Guide. Diamondback moth Page 55 of 92. Introduction, feeding habits, damage, appearance, conditions favourable to DBM, monitoring, control advice, and mechanisms of resistance. Published 2009.

NIPI - Diamondback moth Information on finding, monitoring and recording, beneficial insects, control, thresholds, multi pest considerations, and communication on management. Published 2014.

PIRSA DAFWA & CESAR - I Spy Manual. Diamondback moth Section 3, page 21. Pest ID key of Canola. Section 4, pages 13-14. Distinguishing characteristics, crops attacked/ host range, damage, confused with, distribution, pest status and risk period, monitoring/sampling, and management. Published 2012.