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Awful gingers!

July 16, 2010

The ornamental torch ginger (Etlingera elatior) is commonly grown in Chiang Mai in northern Thailand. Sometimes, the flowers turn brown even before they open, and the pseudostems turn brownish too. If you look carefully, you will see holes in the pseudostems. This is due to a stem borer often identified as Conogethes punctiferalis, or the ‘yellow peach moth’. This insect is claimed to attack many different plants, from cotton to ginger and longan. It is possible though, that there is a complex of many similar species. Anyhow, the larvae seem to focus at one food source at a time, so the best way of striking back is to cut down all your sick gingers. That will kill the larvae inside the pseudostems, and you disrupt the reproductive cycle. Of course you need to compensate the gingers for the loss of nutrients, by adding some old manure. If you see the pupa, or rather the frass covering the pupa, hanging from a leaf, then you have waited too long. The moth is attacked by a parasitoid fly (Argyrophylax proclinata), which eventually will keep the population at tolerable numbers. If you spray a surface insecticide on the gingers, while the larvae are inside, you will just kill innocent insects. Commercial ginger farms in India spray 0.1% malathion (a neurotoxin like temephos) throughout the rainy season, so that the larvae can never enter inside. Resorts and sales nurseries usually spray this compound regularly on any plant, regardless if there is an attack or not. 

Eric Danell

The pupa of the yellow peach moth is surrounded by a tough cocoon, which in turn is covered with frass. The pupa is firmly attached to the undersides of the host plant’s leaves.

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