Codlin Moth is a major pest for some orchid growers, me included, in Melbourne’s eastern suburbs – once home to many fruit orchards. The codlin moth that once infested these orchards is still present in large numbers, thriving on other plants, including orchids. It is a small, brown moth that can be seen in flight, often in large numbers, during the warmer months. It lays its eggs on the new growths and flower spikes of various orchids. These eggs hatch to produce small, yellowish caterpillars that then burrow into the new growths and flower spikes. Their presence is often undetected until the growths and spikes collapse or the caterpillars’ small brown droppings are noticed.
Cymbidiums and Australian native dendrobiums seem to be worst affected. New cymbidium growths sometimes rot off soon after they emerge, while flower spikes often collapse when the first buds emerge from the sheath. Most, if not all, of the new growths of native dendrobiums may be attacked, ruining the vigour of the plants. I find that regular spraying throughout the warmer months of the year with Carbaryl and systemic insecticides such as Rogor® or Lebaycid® provides effective control. Beginning in October, I spray every three weeks until April. Great care must be taken when applying these sprays. I always wear gumboots, a disposable coverall with hood, rubber gloves and a gas mask with the correct filters (which must be replaced regularly, regardless of how often they have been used). I spray only in calm weather, making sure that any breeze is at my back. To make doubly sure of safety, I always shower and change my clothing after spraying.
The above spraying regime will also kill other types of caterpillar, mealy bugs, scale, aphids and thrips. Less toxic pyrethrum sprays may be used to control occasional outbreaks of aphids. Cockroaches and ants are easily controlled by spraying Yates Ant and Roach Killer® onto the pots, benches and walls of the shade house, where it has a residual effect. Snails, garlic snails and slugs may be controlled with Baysol® or Blitzem® pellets or sprays. Occasionally I use tomato dust, which contains carbaryl, copper and sulphur, to control some caterpillars, garlic snails and some fungal diseases. I apply this dust with a bellows’ type dust gun. Provided it is only partly filled it gives a fine, even covering of dust without any heavy concentrations that may burn some young growths. Always take safety precautions while applying any toxic sprays or dusts.
This article first appeared in the Australian Orchid Foundation’s publication Orchids in Australia: Growing Orchids: Common Cultural Problems and their Solutions, edited by B. Milligan and A. Hope (2005).