Diamondback Moth

Diamondback moths are slender, grey – brown in colour, measuring about 10 mm long, with a 10 mm wingspan. Diamondback moths have a distinct white stripe down the centre of their back. When moths are at rest, this forms the pattern of diamonds, which is less obvious in males. Eggs are oval, pale yellow and about 0.5 mm in length. Larvae are pale yellow-green, reaching 10 – 12 mm in length when mature. Pupae are cream-green, darkening in colour prior to the adult moth emerging.

Female moths can produce up to 150 eggs throughout their life either singularly or in clusters along leaf veins, shortly after mating. Eggs hatch in about 4-6 days. First instars tunnel into leaf tissue. Larvae go through four instar stages before they pupate. The rate of development from eggs to moths depends on temperature, faster in warm weather and slower in cool weather. At 28°C the lifecycle takes 14 days, whereas at 12°C the lifecycle takes more than 100 days.

Larvae chew holes known as windows when they feed on the underside of leaves. In brassica vegetable crops larvae can burrow into the heads of cabbage, Brussels sprouts or broccoli, making control difficult. Damage due to feeding can render produce unfit for sale.

To avoid further insecticide resistance developing in DBM populations, management, and control requires an integrated approach, combining cultural, biological and chemical methods. To reduce larvae numbers building up, it’s important to control volunteer host crops and weeds. Avoid early sowing of susceptible crops into paddocks which have a history of DBM. Diamondback moths can migrate long distances on winds, so where possible, separate blocks of plantings to avoid spread of DBM. Plant healthy seedlings and slash or turn in old crop residues after harvest.

Several naturally occurring predators and parasitoids attack DBM (e.g. Diadegma semiclausum wasp), which provide some level of control. To preserve these populations, it is important to limit the use of broad-spectrum insecticides.

Monitor crops from late winter to late spring for the presence of larvae. The use of pheromone traps can be used in brassica vegetables to monitor DBM, however this should not replace crop monitoring.

Biological insecticides containing Bacillus thuringiensis (Bt) have been shown to be effective against DBM. Follow Bt application directions to ensure best results and rotate insecticides as per crop and regional resistance management guidelines.

If DBM thresholds are reached in crop, an application with an insecticide such as Belt®, which is soft on beneficial insects should be applied. Belt is best applied to target young larvae and is registered for the use in brassica vegetable crops. Movento® provides another soft option for the control of DBM in leafy brassica and brassica vegetable crops, making it ideal for use in an integrated pest management system. Movento should be applied when larvae are small.

References

Agriculture Victoria (2021), ‘Diamondback moth’, Diamondback moth | Priority pest insects and mites | Pest insects and mites | Biosecurity | Agriculture Victoria

Baker, G and Kimber, B (2015), ‘Diamondback moth’, PestNotes Southern, South Australian Research and Development Initiative (SARDI), Diamondback_Moth.pdf (pir.sa.gov.au)

Department of Primary Industries and Regional Development (DPIRD),(2017), ‘Diagnosing diamondback moth, DPIRD, Diagnosing diamondback moth | Agriculture and Food

Dimsey, R, Carey, D and Henderson, S (2010), ‘Brassica Best Practice Integrated Pest Management’, Department of Primary Industries, Ausveg page 16, TL197.pdf (ausveg.com.au)

Grains Research & Development Corporation (GRDC) (2020), ‘ Diamondback moth best management practice’, Southern Region, Diamondback moth best management practice guide - southern - GRDC

Grains Research & Development Corporation (GRDC),(2013), ‘Diamondback moth is a sporadic but serious canola challenge’, GRDC Southern and Western Regions Fact Sheet, grdcfsdbmlow-respdf.pdf.pdf

Queensland Government (2017), ‘ Diamondback moth, Department of Agriculture and Fisheries, Diamondback moth | Department of Agriculture and Fisheries, Queensland (daf.qld.gov.au)