Codling moth mating disruption pheromone rings (against “worms” in apples)
Hawi Winter PhD MSc, Waikato Branch
Few things spoil the taste of a home-grown apple faster than discovering a “worm” inside. For orchardists and backyard growers alike, codling moth can be a persistent frustration – but pheromone mating disruption offers a clever, low-toxicity way to reduce damage without relying on conventional sprays. In this practical guide, Hawi Winter explains how the rings work, when to use them, and what results growers can realistically expect.
The enemy: codling moth (Cydia pomonella)
Codling moths are members of the butterfly/moth order (Lepidoptera). They are major pests in apples, pears, nashis, quinces and walnuts. It is the larval state that is annoying for us growers. When you find a worm in your apple, it is actually not a worm, but the caterpillar instar of the moth.
How do codling moths reproduce?
Codling moths reproduce by complete metamorphosis (e.g. egg to caterpillar to pupa to moth) starting in spring with the emergence of adult moths from overwintered pupae. The nocturnal female moths signal to the males their readiness to mate by releasing a pheromone scent. Males approach the females upwind, guided by the scent of codlemone, the sex pheromone specific to codling moths.
The principle of mating disruption
Codlemone can be synthesised on an industrial scale; it is a white powder that evaporates (sublimes) slowly over several months. It is not a poisonous insecticide. It can be co-extruded with or put inside plastic carriers. If you put these plastic carriers into your orchard, you saturate the air with the scent (unnoticeable to humans or other animals), which confuses or misleads the male moths. They don’t find the females because their scent is overpowered by the artificial scent. Hence, no mating, no fertilised eggs, no offspring (caterpillars/worms) in your apples.
Pheromone products available
There are so-called codling moth traps available in garden centres. They trap codling moths on a sticky surface inside hanging box structures. The lure is the sex pheromone of the female, therefore catching only males. These traps were originally developed as monitoring tools. Once you detect codling moths on the sticky surface, you are alerted to their presence and you are then supposed to spray with pesticide. These monitoring traps do not work as mating disruptors over greater distances/areas. Because they are expensive, most people probably don’t use them.
Plastic pheromone mating disruptor rings are the products we use in our orchards. They are little loops or rings that don’t kill but confuse the male codling moths. The pheromone will diffuse out of the plastic as vapour, becoming airborne and wafting through the orchard for about eight to 10 months. The scent is many times stronger than that of the female codling moths. The resident females will eventually lay unfertilised eggs.
The main brands are Isomate and NoMate; both work well.
There are also pheromone mating disruptor rings available that combat several pests like codling moths plus leaf rollers etc. I found them less effective against codling moths. After all, you can only pack so much pheromone into a little plastic ring and I think that codling moths are the main insect pest in pipfruit in New Zealand. I therefore use the one effective against codling moth only.
Why can’t I buy the products in a garden centre?
The manufacturers are aiming to supply large-scale commercial pipfruit orchards. Marketing these mating disruptor rings as retail items is difficult due to the time restraints of the application. You can buy the mating disruptor rings at leading horticulture supply outlets in packs of 400, but you need to order these packs well in advance due to the limited shelf life of the product. They come from Japan or the USA. The importers don’t sell directly to the customers.
Packaging sub-lots of 400
I started sourcing and using these some seven or eight years ago. This gave me the opportunity to trial and test the mating disruptor rings in smaller orchard lots. The manufacturers did not recommend their use in small home orchards. By now we know that the minimum number of rings should be 10 per orchard to be effective. Handling mating disruptor rings in the orchard did not affect me (wearing rubber gloves), but re-packaging the rings in my workshop made me nauseous. I therefore wear protective gear nowadays.
Timing
The timing of hanging up the rings in tune with the lifecycle of the codling moth is crucial. The rings should be in the trees by the start of the bud-break of blossoms, when codling moth mating starts. The rings work for one cropping season and need to be replaced annually. Deploying the rings earlier than October is OK, we apply them in the northern Waikato in the last week of September.
Practical considerations
The best method is if you hang one ring per 12 m (or less) in any direction, at about two to four metres in height (in the upper third of the tree canopy). In our orchards I put one ring in every tree, plus some in the periphery on any type of tree. For a small domestic orchard, I recommend one ring per tree plus some in the periphery.
It is important to safeguard the surrounding area by hanging up rings in trees other than pipfruit trees. This will hopefully create a buffer zone that reduces the migration of fertilised female codling moths into your orchard from outside your control area. Apparently, the dispersal range of codling moths is about 300 m.
It takes some time to reduce the population density of codling moth in heavily infested areas; I have observed an improvement over several years in our orchards.
Involving neighbours in the fight against codling moths is obviously an advisable thing, because that extends the buffer zone around your orchard and fewer fertilised female codling moths will drift into your area.
Hanging and removal
One can manually hang smaller numbers of rings (use rubber gloves), but I have devised home-made installation tools using first a bent #8 fence wire, and then a nasal speculum on two metre poles. Removal at the end of the growing season is not necessary, because of the flexibility of the rings. They will fall off if the branch increases its girth and can then be collected from the ground for disposal.
Results and limitations
You will NOT eradicate all codling moths with mating disruptor rings. We have seen a reduction of approximately 98% infested apples down to to 5%. The reasons for not achieving complete eradication are most likely migration of fertilised female codling moths from surrounding areas like neighbouring properties and probably accidental meetings of males and females.
Economy
The rings cost between NZ$2 – 4 per ring plus postage. Stockpiling for next year is not recommended, because the rings evaporate the active ingredient, the pheromone. Fresh is best. Still, if you are happy with a reduced efficacy, you can freeze surplus rings in a glass container with an air-tight metal lid at -18°C in a freezer (the pheromone fumes can tunnel through plastic bags in your freezer and contaminate food).
Common misperceptions and answers to FAQs.
The pheromone rings work specifically to interrupt the mating and reproduction of codling moths; they don’t work for guava moths because they have different pheromones.
You won’t achieve better results if you place several rings in one apple tree and none in the other trees. You must spread the pheromone carriers out.
Rain does not influence the viability of the rings.
There are several generations of codling moth (up to four or five) in one growing season; the rings work for the whole season.
Pheromone mating disruptor rings are acknowledged as an organic input.
Links to the MSDS and more information will be distributed via email on request.
How to get the rings?
Send an email to nocodlingmoths@gmail.com for more information. Keep the season timing in mind!
