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Codling Moth
...a common pest in apples and pears
(and walnuts, and sometimes in other fruit such as peaches or nectarines).
What is it?
This is the "worm" in your apple. It is the larva of a small moth. The egg is deposited on the young fruit or nearby leaves and the caterpillar hatches and burrows into the fruit, usually from the blossom end.
What is the life cycle?
Pupa overwinter in bark, adults emerge in spring.
Adults deposit eggs when the temperatures are warm enough (62F at sunset), which usually is when the tree is just past full bloom--usually April.
The first larva infest fruit, drop from the tree, then try to crawl back up--usually May. They pupate, hatch in late spring; these new moths lay eggs in the developing fruit. Badly damaged fruit drops; the larva crawl out and try to crawl back up again--usually July-August.
This cycle can continue as long as night temperatures are warm enough--well into October in our area.
The female moths usually begin laying their eggs (ovipositing) just after the tree flowers. This can vary from the time of blossom to as much as a few weeks later, depending on temperatures. The key time is "50% petal drop": the tree is just past full bloom, and there is a carpet of petals on the ground. So buy and install traps, used to monitor them, when the tree is just starting to bloom.
How to manage it?
Organic control measures include: Pheromone traps (put in trees during bloom). The traps used for monitoring give some level of control; two traps in a back yard tree may reduce the number of wormy apples.
Cleaning up the infested fruit. Picking up the wormy apples that drop is very important in preventing the secondary infestation that occurs in the late spring. Worms will crawl out of the apples and back up the tree.
Beneficial nematodes may help control the larva that are in the fruit which has dropped. Picking up and disposing of that fruit is probably more effective.
Putting bands of rags or corrugated cardboard on the trunks to block larva which are crawling back up the tree. This prevents the second generation (there may be as many as 3 - 4 generations per year). The larva try to pupate in the cardboard, or are blocked physically by the rag (so make it a tight fit, and don't forget to remove it at the end of the season).
Releasing natural predators. A tiny parasitic wasp sometimes released for control of codling moth is Trichogramma wasp. We sell an empty box that customer can mail to Orcon to have the wasps mailed back. Timing is early spring when moths are being caught in traps and sunset temperatures are at +/- 62F--typically just after the bloom ends. (This is also when spraying is done, if chemical control is being used. The sprays kill the Trichogramma, so the methods are not compatible.) Releases are only partially effective.
Chemical sprays are used by commercial growers to keep the infestation to 10 - 20%. Homeowners may get sufficient fruit, even with higher levels of infestation, without spraying by following all the other practices listed.
Desperate? You can enclose the fruit in No. 2 paper bags (lunch bag size) when they are less than an inch in diameter. This is a way of guaranteeing at least some clean fruit if your tree is in a highly infested area. If a neighbor's tree is heavily infested and no control measures are being applied, this may be the only way to get clean fruit.
If this all makes it sound as though it is difficult to control codling moth in a home orchard, that is because it IS. It's a frustrating pest when you get it, and the population increases year after year. Nearby infested trees will infest your fruit. Codling moth is the major reason that pears and apples are less popular for home orchards than stone fruits, persimmons, figs, pomegranates, and citrus.
What to spray?
Pesticides labeled for codling moth include spinosad and malathion. The first is an organic control.
The timing is crucial: put out the traps and watch for the female moths, then spray 2 - 3 times at 2 week intervals. This is roughly from the time of "50% petal drop" (i.e., the tree is in full bloom with a carpet of petals on the ground), but varies from year to year.
A useful fact is that mating occurs when the temperature in the late afternoon is 62F or above. They won't start laying eggs until we've been at that temperature for a couple of days.
Do winter dormant sprays help?
The dormant sprays that you do in the winter will not control codling moth. These are done to control fungus and help prevent overwintering aphids.
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© 2008 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
www.redwoodbarn.com
Feel free to copy and distribute this article with attribution to this author.
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