Wednesday, June 21, 2017

Outsmarting the codling moth

Codling Moth infestations were really bad in Tasmania last summer. This post explains the Codling Moth’s life cycle and a range of pest control measures that can be put in place to make the coming fruit season much more successful.

The life and times of the Codling Moth

The life cycle of the Codling Moth is quite interesting when you look into it, and the better you understand it, the better you can respond to it. So here we go:
  • Codling Moths come out of cocoons on or near fruit trees in Spring when fruit blossom buds begin to open and nights are dry and not cold.
photo Dept. of Agriculture and Food Western Australia
  • They flutter around in the evening, eat nectar (adult moths don’t eat fruit), and mate. Wind may take them quite a distance away from where they emerged, possibly to a fruit tree in your garden.
  • When temperatures reach 15 degrees Codling Moths lay 50 – 60 eggs usually on leaves or fruit of apple, pear, nashi pear, crab apple and quince trees (sporadically also on walnut and stone fruit). 
  • The eggs are tiny and nearly transparent, and hatch in ten days. 
  • The small young caterpillars that emerge make their way to the nearest fruit they can find. They burrow into the fruit (often at the top or bottom). They head for the core, and stay there for 3 – 5 weeks, while eating and growing to full size.
  • After having lived inside a fruit for 3-5 weeks, fully-grown caterpillars burrow themselves to the surface of the fruit (telltale signs include lots of ‘frass’ - reddish-brown droppings on the surface of the fruit) and move to a suitable spot to form a cocoon (a crack, crevice, loose bark or other tight space in the trunk of the tree, or debris or mulch or soil under the tree, or a nearby tree support).
A cocoon removed from under bark - photo by R. Knox (Agriculture Western Australia)
  • The cocoon hatches after a few weeks, and a new Codling Moth emerges. Back to the second dot point and the cycle continues, until temperatures drop to under 15 degrees. In warm locations protected from sea breeze this resulted in three generations of Codling Moths in our recent long summers. All three generations visited the same fruit. No wonder there was hardly a fruit left with a Codling Moth hole. 
  • The last generation of caterpillars pass through winter dormant in their cocoon, and the cycle resumes at the first dot point. 

I asked entomologist (insect-scientist) and Food Garden Group member Margaret W what would happen if the first caterpillar generation of the season hatched early and there wasn’t any fruit yet? Would they all die? Margaret explained that this scenario simply will not happen because the moth responds to the exact same weather signals as the tree. The caterpillars are 'in sync' with the tree.  There simply will be fruit when Codling Moth caterpillars need it.  Wow!



Disrupting this life cycle


The Safe Pest Control series of blog posts on this blog describes six steps to get rid of vegie garden pests. For the Codling Moth we will use the same steps and do specific things to disrupt the moth’s life cycle described above.

There are bound to be many over-wintering moth cocoons at the start of this season, so apply as many of the methods described below as you can, instead of just relying on one strategy to work.


What trees to buy and how to maintain your fruit tree area


There are many things you can do to make your fruit tree area ‘moth-unfriendly’.

The home gardener with a small number of trees can employ an important method in the combat against the Codling Moth: checking individual fruit. Why is this important?

When you see a little hole in a fruit, the damage is done. Does it not make sense to let this fruit ripen and use the parts of it that are unaffected? The answer is a resounding ’no’! By doing so you will allow a caterpillar that is in the fruit to escape and create more generations of Codling Moth that very same season that will affect other fruits in your garden. Immediately pick affected fruit and remove it from the garden. Don’t put it in your compost. Remove it from your garden and destroy.

During the season regularly check all fruit on apple, pear, nashi pear, crab apple and quince trees. ‘Easier said than done’ you may say. You can’t do this if your trees are high and wide, so the number one suggestion on the way to combating the Codling Moth is to make sure that all fruits at workable heights, so you can reach them and inspect them:
  • When you buy fruit trees get fruit trees on dwarf or semi-dwarf root stock 
  • Keep trees pruned to a size that allows you to inspect all fruits, or espalier trees 
  • Consider early-maturing varieties to avoid the third generation of Codling Moth, which is often the most devastating. 
Mulching is a great way of keeping orchard soil moist. Mulch also provides habitat for ants, spiders and predatory ground beetles, which feed on Codling Moth larvae. Codling Moth larvae will come down a tree if they did not find a suitable spot to make their cocoon on the tree. Make sure that when they reach the ground they don’t find any suitable spots there either, by keeping mulch well away from the base of the tree.

Chooks or other animals that free-range under the trees and eat fallen fruit and larvae are a great way to help contain moths. Instead of you having to pick up and dispose of damaged fruit, the chooks will do it for you. Just do not introduce them into a young orchard, as they will scratch at mulch and expose roots.

Birds and predatory insects are an important means of Codling Moth control. If you have flowers in your fruit tree area, they will come, and they will eat Codling Moth caterpillars, moths and cocoons. Dill, Coriander, Alyssum and Cosmos are said to attract parasitic wasps and other helpful bugs. Wasps are so successful in reducing moth numbers that they are commercially produced in Australia and used in orchards for this purpose, but the available pack sizes and therefore cost make it inappropriate for use in home garden orchards. More info can be found here: 


At the start of the season – June to August

With three generations of Codling Moth in one season it is important to reduce numbers as early as possible in the season.

Start your campaign against the Codling Moth in June – August by doing the following start-of-season cleanup:
  1. Remove pieces of flaking bark, broken branches, leaf debris and other litter from the tree. Squash any over-wintering cocoons you find. 
  2. Remove ladders, old boxes, stakes and other tree props after checking them for cocoons. 
  3. You may not want to remove sturdy tree supports because the tree will continue to benefit from them. Inspect these supports thoroughly. 
  4. Check nearby wooden fences. 
  5. Remove any bands and traps (see below) that were around the tree trunk last season. 
  6. Remove leaf litter and mulch around the base of the tree. Don’t re-use this elsewhere in the garden or on the compost heap, but dispose of it in your rubbish bin or burn it. 
It is recommended that everyone with fruit trees undertakes this start of season cleanup, regardless of whether they might get Codling Moths or not.


But I may not get any Codling Moths


You were lucky if you did not get any Codling Moths last season. Consider how many over-wintering moths there will be eager to fly out at the start of this coming season. It will be best to assume you are going to get them (again). However, if you decide to only take action once you have proof you have any, there are two ways to find out before you find telltale holes in your fruit.

Hang a jar with a sweet liquid off a tree in the middle of your fruit tree area. A small amount of molasses or sugar or honey mixed with water - enough to cover the bottom of the jar – will do the trick because Codling Moths look for nectar and other sweet liquids. Pour a thin film of vegetable oil over the mix to stop moths from escaping. Check the jar regularly and take action (see below) when you catch a Codling Moth. This jar will attract other moths as well, so it is important that people know what a Codling Moth looks like (see first photo in this post). This no-cost trap may miss some moths and it is not an effective means of pest control.

Commercial orchardists use pheromone traps to determine when to start their expensive pest control measures. The traps release a non-toxic sex-attractant that only attracts male Codling Moths. The moths then get stuck in the glue in the trap.

This is a great example of pest control that is not broad-spectrum, ie. it only destroys the intended target, no other (beneficial) insects. Pheromone traps are non-toxic to humans.

A pheromone trap under construction
The photo shows, in the foreground, a little cream pheromone lure that was put in the middle of a surface coated with glue. This is then inserted in the housing shown behind it.

A pheromone trap in action
Home gardeners can use the pheromone trap as one of their methods of catching moths. Use them from the time trees are first blooming until temperatures go down at the end of summer. A trap with five pheromone sachets (each sachet will last five weeks) will cover the whole season and cost around $45 (2017 – Australia) (for sale at hardware stores and on the net). Additional sachets for subsequent years are a lot cheaper.

Have this trap in place from the time blossoms open until top day temperatures drop under 15 degrees.


During the season

Once every ten days from blossoming time until the end of the season:

  • Look for and remove flaking bark, broken branches, leaf debris and other litter from the tree. 
  • Collect any fruit you find with small holes, and destroy it. In a long season three generations of Codling Moths will hatch. Leaving a fruit on the tree because you can’t bring yourself to waste it, will enable the moth to generate more off-spring that will affect more fruit. Do not leave affected fruit lying around. Don’t put it in your compost heap. 
  • Collect and remove all fallen fruit. 
  • Check mulch to make sure it is well away from the base of trees. 
  • Change pheromone sachets if their five week period has expired 
  • Check other types of traps (see below) that you added. 
Once you have done this a couple of times it becomes second nature and very little work.


At the end of the season


After all fruit has been harvested and before leaves drop prune your fruit trees so you can once again reach all fruit next season. Make sure that no branch, especially when laden, is ever likely to touch the ground.


More types of traps


Having removed all suitable spots on a tree for caterpillars to form cocoons, they will move down the tree in search of a suitable spot in leaf litter, mulch or soil around the tree.

Cocoon traps are simple traps consisting of a double layer of hessian (see photo below) or even cardboard, held in place with a piece of string around the base of a fruit tree just above the ground. No glue or anything else is needed. This trap provides a great place for Codling Moth caterpillars to form cocoons.

Just be alert to the fact that you must check this trap thoroughly every ten days and destroy cocoons you find, otherwise you provide ideal accommodation for many cocoons, and Codling Moths will love you for it. This simple trap is specifically for moth cocoons. No other (beneficial) insect is harmed.

Ideally it is in place from when blossoms open until late Autumn. Only replace it if it no longer is the nice dry hiding place it was when you first installed it.

You could add the same traps along limbs of the tree. Just remember to check them regularly!

A cocoon trap
Evolution has not yet created caterpillars that can fly or swing themselves from tree to tree, so this is a cheap and effective method to trap cocoons, provided you check and destroy regularly.

Grease bands are ready-to-use non-toxic inexpensive bands that are for sale in hardware stores and nurseries. They trap all insects that touch it, including Codling Moth caterpillars. They are what is called ‘broad spectrum’. They will catch a lot of insects other than Codling Moth caterpillars.

Choose a smooth area on the trunk not too far from the ground. Cut a strip of the band material so you have a generous overlap and fit tightly so insects can’t pass under the band. You may need to put a piece of string around if it does not fit tightly. The glue needs to face to the outside and is very sticky. You can wash it off your hands with dish-washing liquid.

Check this trap regularly to make sure it does not slip, and replace it when covered with dust or insects.

Don’t use this trap as your only moth-control measure as many moths will simply fly to leaves and fruit and never travel up or down the trunk of the tree.

A grease band
Remove the band at the end of the season as it is made out of strong material and will restrict the tree trunk from widening if left in place indefinitely.

Horticultural glue traps work very similarly and are also broad-spectrum.

Horticultural glue is a product that is non-toxic to humans and that can be bought from hardware stores and nurseries. Put a band around the tree trunk before applying the horticultural glue. Young trees with a thin sensitive bark may die if glue is applied directly to the bark.

Use a slightly elastic, rot-proof, non-sticky tape (at least 100 mm. wide) or some other waterproof banding material (you could use kitchen glad wrap). Wrap it around the tree trunk near the ground and make sure the material is tight enough so moths can’t pass under it. 

This trap will remain effective until it is covered with insects or dust.


Exclusion


Blocking access to individual fruits by bagging them is a great choice for home gardeners who have a limited amount of fruit because:
  1. Your fruit will remain undamaged, which is what all this is about. 
  2. Access to fruit is a crucial part of the Codling Moth’s life cycle. Stopping this means stopping the moth’s reproductive cycle in your local environment, provided you bag all fruit. 
  3. It is also totally effective against birds and possums. 
  4. Effective exclusion makes all other moth pest control measures completely unnecessary. 
There are several products especially made for this purpose: 
  • waxed paper bags with a built-in twist tie 
  • special nylon stocking bags with a draw string
You can also use nylon stockings for this purpose if they don’t have holes.  For more info about these products see for instance here.
After thinning fruit to just one piece per cluster, remaining fruits are put in a bag while still very small (around 4 – 6 weeks after flowering). Check bags for holes when putting in place and occasionally during the season. If you are reluctant to thin fruit, realise that this needs to be done anyway so the remaining ones become a good size, and because branches may break if you leave all fruit on the tree. Failure to thin fruit also the cause of ‘biennial bearing’, ie. a large crop one year and none the next.

Commercial growers may spray fruit before bagging just in case a small caterpillar is already present (spraying suggestions – see below).

Bags should be removed a week before picking to allow fruit to develop a stronger colour.

Some fruit varieties with short stems (eg. Gravenstein apples) may create a bit of a challenge.

Netting a whole tree works too of course if netting-holes are very small and the net is very carefully dug in at ground level.


Spraying

There are some low-toxicity pesticides that can be used against the Codling Moth:

  • Dipel, also known as Bt (for Bacillus thuringiensis), is used against white butterfly caterpillars on brassica, but it is equally successful against caterpillars of the Codling Moth. Spray the whole tree once a week from when fruit is 10mm. in size, or after rain, whichever comes first.
  • Eco Oil can be used to smother Codling Moth eggs. Also, adult moths will not want to land on a surface that is coated with oil. Consistent re-spraying may be necessary to control new eggs and to compensate for rain washing the oil off the surface of the leaves. Begin spraying at petal fall.
  • Spinetoram sprays, such as Success Ultra, are derived from naturally occurring soil bacteria. Spinetoram has low toxicity for humans, but a higher risk for pets eg. dogs. Spray the whole tree every fortnight from when fruit is 10mm. in size. For sale at any hardware store.
  • White oil can be sprayed to smother eggs and prevent them from hatching. Mix one part of white oil with fifty parts of water. Apply this at weekly intervals throughout the season.
  • Pyrethrum can be used to control adult moths and to kill tiny caterpillars before they enter fruit. Pyrethrum is harmful to beneficial insects.
Of these five pesticides only Dipel is not broad-spectrum. The other pesticides also kill other (beneficial) insects.

For general notes about spraying and the products above see the last post of this blog’s Pest Control series at http://foodgardengroup.blogspot.com.au/2016/03/safe-pest-control-step-5-and-6.html

Do not spray when very hot or when trees are suffering from drought stress. Pick a still day where no rain is expected for at least 6 hours. Make sure you don’t eat fruit within withholding periods.


Thank you!
Two members of the Food Garden Group, Margaret W (entomologist) and Max K (fruit tree professional) read a draft of this post and provided additional info and feedback! Many thanks to you both.



1 comment:

  1. Wow Max ! Thank you for all your research and efforts for bringing us this very valuable information. I think last year I must have had 10 generations at once and thus very few apples were grown without the tell tale signs of these bugs. I will try harder next season and use my chooks more. Cheers Ross (Roscoe ) Thomas

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