Codling moth

Codling moth (Cydia pomonella)is one of the most common pests in New Zealand orchards.

It infests all pipfruit (apples, pears, quince, crabapples, nashi) and walnuts with its caterpillar which feeds for three weeks inside the fruit. Signs are an infected core and access hole ringed with brown frass.

Natural controls have not proved effective in New Zealand - yet.

  • The little wax-eye birds (silver eye, white eye, Zosterops lateralis) will dig out over-wintering pupae, but not usually enough to be an effective control.
  • A parasitic wasp specific to codling, Liotrophon caudatus was released in New Zealand in 1906 and though it has survived (in unsprayed orchards), it has not killed enough codling to reduce the population.
  • Since 2012, Plant and Food Research have been releasing Mastrus ridens, another wasp which will lay its parasitic eggs in the eggs of the codling moth. Over 60,000 have been bred and released in the commercial apple regions of Hawkes Bay, Nelson/Motueka and Central Otago.
  • There are several organic methods to control codling numbers in your orchards. Unfortunately, some commonly known ones are not particularly effective and all the methods target different stages of the life cycle so it is important to be doing the right one at the right time of year.

Winter

During winter the pupae spin a silken cocoon in a crevice or under bark and await temperatures of 15°C.

Strategy:

Clean up all fallen fruit and litter from under the trees - you don’t want any hidden habitats they can overwinter in.

Having chickens running under the trees may seem a solution, but Carabid beetles and disease will kill any codling on the ground and those who have trees both in and outside the chicken pen say there is no difference in the codling levels.

An old remedy is to wrap the tree trunk in corrugated cardboard. The theory is that the caterpillar will find that an attractive hiddey hole and spin their cocoon in there. You can then remove and burn it before they hatch in spring. The problem is there are lots of places further up the branches they can choose to hibernate and there can be several generations a year. To be most effective, place the cardboard as high up the trunk as possible (but below any fruit), grease or make a sticky band below the cardboard to stop them passing on by and remove and burn frequently from early summer to after harvest. Even then you will only be destroying a proportion of the codling cocoon.

Spring

This is the start of their active life cycle. Once the blossoms start showing pink colour the pupa develops the features of an adult moth and emerges late in spring (about petal fall). Adults will continue to emerge for several weeks and are most active on warm evenings. They will mate and the female will singularly lay tiny eggs (about 1mm) on or near developing fruit. These eggs take 8-14 days to hatch into tiny larvae and crawl inside the fruit. This is the most effective time to attack and there are several strategies:

Disrupt mating

Pheromone traps are commonly available at garden centres or hardware stores. They have a lure, a sticky trap base and a triangular cover to hang in the tree. These use the female mating scent to attract males.

To use them as a form of control is like putting a pub on the corner and hoping it will stop teenage pregnancies. Males can mate many times and a mated female can lay as many as 200 eggs. You would have to trap every male as a virgin to be effective.

However the traps are a useful way to monitor when the moths are active (so you can spray). They are only effective if the sticky base is sticky and dust can quickly coat them. Fold them in half and then re-open to restore the sticky tendrils and extend their effectiveness.

Pheromone disruptors

Organic pheromone mating dispensers are a twist tie that you slip over a branch at the beginning of the season. Applied at 100 to the hectare, they expel the female scent to such a degree it confuses the male and prevents mating. Trapping in the sticky base trap should shut down if they are working effectively.

They are not easy to source (try emailing Suzanne at This email address is being protected from spambots. You need JavaScript enabled to view it.) and though well regarded, I tried them for two years running with little noticeable effect. However I have three closely-planted apple trees that are badly infected, these are apparently more effective when used with low density of codling spread over a wide area/larger orchard.

Kill the eggs

Neem oil, conqueror oil or any oil spray will smother and kill the eggs. To be effective, this must be repeated at 8 day intervals until your traps show the adults have stopped flying and laying and full cover of the eggs must be achieved – spray under and over.

Kill the emerging larvae before it enters the fruit.

This is approximately at petal fall, and needs to be repeated for success.

You can use any spray at this stage that is effective against caterpillars. Be aware that organic pyrethrum sprays and homemade garlic sprays will also affect beneficial insects, including your pollinating bees.

There are two organic sprays which are more specific. Available at garden centres in sachets is the Kiwicare organic caterpillar biocontrol. It does not list the codling as a target (it is aimed at white butterfly, leaf rollers, looper and other caterpillars) but the Bacillus thuringiensis it contains is effective against the codling caterpillar.

The other is available through horticultural supply stores and is branded as Madex-3. This contains the Cydia pomonella granulises virus which is specific to the codling moth. It comes in 100ml to mix in 2000 litres to do a hectare and costs around $125 so is only economical for those with larger orchards.

Both need to be repeated until 10 days after the monitoring traps show the adults are no longer active to catch the emerging caterpillar. Once the caterpillar is inside the fruit it is safe from sprays.

Summer

The caterpillar will spend about three weeks gorging itself on the flesh of your apple, before emerging to seek a hidey hole to make it’s cocoon (see winter notes). North of Auckland, they commonly hatch a second generation about November and theoretically can have more generations in one year depending on the temperatures. Further south, the records show it to be more a single long stretch of activity.

Use traps to monitor and spray larvae 10 days after peak periods, and/or to catch adult moths.

Trapping adults

Moth traps can be used to significantly reduce numbers. While these have proven successful for me in the past, they were not effective enough in themselves for adequate control. There is no way to ensure you catch the female before she has laid her eggs.

However other users have found them to be very effective, almost totally eradicating within three years and swear by them.

I found all three types equally effective. Put out by mid blossom and maintain until after harvest in March to catch as many moths as possible. You will note the fluctuations in numbers and can use these as indicator traps (spray for larvae 10 days after peak periods) as well. You will need to clean and replenish frequently.

Light traps

Moths are attracted to light – any light or solar light seems to work though LED blue/white lights are said to be better than yellow-hued lights.
A container of water with a little cooking oil floating on top under the light will catch the moths. I have seen everything from corded lights under a Chinese-hat lampshade over a shallow dish, to cheap solar lights with their lens as the container.

Milk bottle traps

Cut an opening in the side of the milk bottle and fill with either of the following recipes – both work. Check after rain and clean out and replace as needed.

  1. Mix 1 litre of warm water with 100g sugar (white or brown), 1 tsp Marmite, 1/2 Tbsp cloudy ammonia and 1/2 Tbsp vanilla and place in milk bottles with an opening cut in the side.
  2. Put 1 tablespoon of vinegar and 1 tablespoon of treacle or molasses in milk bottles with an opening cut in the side and half full with warm water.

Early season infection of the fruit is often by way of the catlyx and can be hard to see. However the caterpillar can be active inside the fruit as indicated by brown frass around the telltale hole. Removing and disposing of infected fruit can help control numbers.

Summary – Recommended organic control for home orchards.

  • Hang moth traps in the tree as soon as blossoms start to appear.
  • Spray with Kiwicare organic caterpillar biocontrol a week to 10 days after traps start catching adult moths. Repeat in 10 days.
  • Refresh traps and leave out to monitor for another generation later on in summer.

 

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