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This leaflet is produced by the Ministry of Agriculture & Livestock, Solomon Islands, with support from IPPSI: 
Improved Plant Protection in Solomon Islands, a project financed by ACIAR, the Australian Centre for 
International Agricultural Research, Canberra. Authors: Authors: Helen Tsatsia, MAL & Grahame Jackson, 
TerraCircle Inc. 

Farmer Fact Sheet 20:

 Diamond Back Moth 

 

 

What is it? 

 

An insect that feeds on plants in the cabbage family - broccoli, cauliflower, Chinese cabbage, 
head cabbage – but also radish, Amaranthus and watercress. The scientific name is Plutella. 

 

What damage does it do? 

 

Caterpillars do the damage. They eat the leaves, making large holes. As the caterpillars grow, 
they tunnel into the centre of head cabbage, cauliflower and broccoli.  

 

How do I identify it? 

 

The caterpillars are light brown at first; when mature, they are dark green, and about 10 mm 
long (photo, right). When disturbed, they wriggle backwards, and drop from the leaf on a silk 
thread. The pupa is often found stuck to the underside of the leaf. The moth is about 10 mm 
long with three, white diamond-shaped patterns on its back (photo, left). 

 

How do I manage the moth? 

 

Cultural control: 

  Start with healthy, insect-free seedlings; this is VERY important; 

  When numbers are low, hand pick the caterpillars; 

  Destroy remains of the last crop, and any weeds belonging to the cabbage family; 

  Grow one crop at a time to prevent insects moving from older to younger crops; 

  If watercress is grown on rafts in the river, sink half the raft for 30 minutes, then the other 

half for 30 minutes. Sink half at a time so you do not drown the spiders; 

  Grow head cabbage from June to November, the cooler time of the year. 

Chemical control: 

  DO NOT use the same insecticide all the time. If you do, the moth will become resistant 

to it. Spray with one insecticide one time, and a different one next time; 

  Choose home-made plant-derived products, such as chili, tobacco or neem;  

  Choose commercial products that contain disease-causing organisms, such as spinosad 

(Success) or Bt - Bacillus thuringiensis; or new chemicals, such as indoxacarb (Steward).