The Husbandman (1538, Holbein)
7 Horticultural Practice
Codling moth is vulnerable to different control techniques at each lifestage, so the descriptions, below, follow the order of lifestages. Because lifestages repeat at least twice during the growing season, it may be necessary to apply the same technique more than once.
Chemical control is dealt with in greater detail in its own section, below. Here the general terms ovicide and larvicide are used to describe compounds that are applied as sprays. Ovicides are applied earlier because their principal mode of action is to slow or stop the development of the eggs. Larvicides are applied later because they act to kill the larvae before they can damage the fruit.
Although codling moth development is more or less synchronized, not all moths will be at the same stage on the same day. For this reason the expectation is that all sprays will be reapplied at least once, treating a cohort of moths, to catch not only the earlier developing moths but the later developing moths as well (except in situations where only very light control is required). The minimum interval before reapplication is listed among the instructions for using each compound and varies according to the kind of spray but is usually around ten days.
Eggs are small and difficult to see, so manual removal is not effective.
7.1.1 Trichogramma Wasp
The Trichogramma wasp inserts its eggs into codling moth eggs, and its larvae consume the moth eggs before they can hatch. Several species exist in nature and may provide background control of codling moth. Culturing and releasing Trichogramma wasps is used as biological control of codling moth in commercial settings where infestation is light, but efficacy varies, treatment is expensive, and the technique is considered unsuitable for the backyard gardener (Brunner).
Granulovirus is also used for biological control of codling moth in commercial settings. It is a virus that infects codling moth larvae. It, too, exists naturally and provides some background control. It is cultured and applied as a spray in commercial settings. It must be applied over the eggs. Then the larvae consume it along with their eggshells after they hatch (Wise et al.). Larvae are not killed outright and may live long enough to cause damage, so this technique is applicable only where infestation is light. Because the virus degrades in sunlight, it must be reapplied frequently while eggs are hatching. As with other means of biological control, efficacy varies, treatment is expensive, and the technique is considered unsuitable for the backyard gardener (U. C. Agriculture and Natural Resources (UCANR), "Management Guidelines").
7.1.3 Chemical Control
Various ovicidal sprays are commercially available and accessible to the backyard gardener. These are divided into those that are more efficacious when applied under the eggs (that is, before the eggs are laid) and those that are more effective over the eggs (that is, applied after the eggs are laid). Some are listed in the "Chemical Control" section, below.
7.1.4 Horticultural Oil
Horticultural oil is a mildly effective ovicide when applied over the eggs and may be used in combination with some chemical controls and with granulovirus (UCANR, "Management Guidelines").
7.2.1 Maggot Barriers
Footies are disposable nylon half-socks that clothing stores give to patrons before trying on shoes. These may be slipped over fruitlets just after the fruit has set to prevent infestation by apple maggots (Rhagoletis pomonella). In fact, they are marketed to backyard gardeners as Maggot Barriers. These are also moderately effective against codling moth. They discourage the larvae from attacking the fruit, but the effort required to bag each fruitlet is extreme, and, although Maggot Barriers are not individually expensive, bagging all the fruit in a backyard orchard can require hundreds. Rather than bag his whole orchard, the backyard gardener may wish to bag only select fruit on certain trees and then rely on other means to reduce infestation of the rest.
7.2.2 Chemical Control
Larvae do not spend a lot of time outside the fruit between hatching and burrowing in, but, while they are still outside, they may be attacked with various larvicidal sprays, which are commercially available and accessible to the backyard gardener. Some are listed in the "Chemical Control" section, below.
7.2.3 Horticultural Oil
Horticultural oil is a mildly effective larvicide and may be combined with some chemical controls (UCANR, "Management Guidelines").
7.2.4 Manual Removal of Infested Fruit
Once the larvae are inside, there are no effective treatments other than removal of each infested fruit by hand. This technique is worthwhile to the backyard gardener, though, who will notice the frass on the outside that the worm produces from within. By removing and destroying infested fruit as soon as it is discovered, he will destroy the larvae before they leave the fruit and thus cut down the codling moth population in his yard.
The gardener naturally desires a massive crop; nevertheless, he must wrestle with his greed while thinning the crop to improve fruit size and to bring the crop load within the bearing capacity of every branch of each tree. Destroying infested fruit is similar to thinning the crop. Both strategies aim to maximize not only the value of the crop but also the long-term productivity of the orchard instead of churning out biomass. Both arouse the same anxiety, and both must be done, anyway, regardless of cognitive dissonance.
In this context, destroying the fruit means treating it in such a way that the larvae in it do not reproduce. Composting fruit is insufficient because larvae can survive unless the compost "cooks" at a high temperature through and through. Backyard gardeners should, if they wish, eat any infested fruit that is ripe enough because processing it dooms the worm within, but this does not mean that infested fruit may be left on the tree from the time it is noticed until it is ripe. Such a delay would allow the worm time to escape. Instead, the infested fruit — ripe or unripe — should be removed from the tree, and fruit not destined to be consumed should, where permitted, be hauled off the premises and immediately incinerated or landfilled as is the case with municipal garbage.
Infested fruit may be fed to livestock. Free ranging poultry consume several insect pests of apples although they are more effective against those that spend time on the ground such as plum curculios (Conotrachelus nenuphar). Presumably, chickens will catch the occasional codling moth larvae as the worms escape from fallen fruit.
The backyard gardener will need to protect those portions of his crop destined for sale from contamination by livestock manure and feedlot dust.
7.2.6 Disposal of Falls
Often, infested fruit that remains on the tree, unnoticed, will drop of its own accord. Mulching within the drip line of the tree makes this "summer drop" easy to spot. All fruit that drops prematurely, whether or not obviously infested with codling moth, should be regularly picked up and destroyed to reduce the possibility that codling moth or any other pest species may escape from it.
7.3.1 Cardboard Bands
It is possible by banding tree trunks and limbs to lure a few mature codling moth larvae to spin cocoons in corrugated cardboard at least two or three inches wide. Use duct tape to secure the cardboard bands with the edges open and the passages parallel to limbs and trunks. These bands may be removed and destroyed before the second flight begins. They may then be replaced with fresh cardboard, which is to be destroyed at the end of the season (Cranshaw).
This works only when tree bark does not provide adequate cocoon locations. Also, if the cardboard bands are not destroyed at the right time, they can actually wind up benefiting the codling moth population. For these reasons, banding trees is not recommended to backyard gardeners.
Woodpeckers must not be discouraged if they are drawn to hunt for cocoons among the trees in the backyard.
The transition from larvae to pupae happens within the cocoons and is, thus, invisible. Control methods, which apply to cocoons, apply to pupae, as well.
The presence of adults may be detected by capturing males in pheromone traps. Ongoing mating activity may then be inferred. Because development of the first flight is synchronized to within a few days, the capture of adult males can be used to synchronize the treatments described, above, too.
7.5.1 Mating Disruption
In commercial-scale operations the same pheromone may be used in much more concentrated amounts to disrupt the mating behavior of most males, but this is effective only for isolated orchards or for orchards extending over several acres, which are not easily accessible to bred females from outside. It is definitely not as effective for the backyard gardener.
7.5.2 Particle Film
Kaolin clay, which is marketed as Surround, may be applied as a spray, creating a particle film on leaves and fruit, which is an irritant that repels females and slows down larvae. Complete coverage is essential. Precipitation will dissipate it and necessitate reapplication.
Bats must not be discouraged if they are drawn to hunt night-flying insects such as codling moths among the trees in the backyard.
7.5.4 Vinegar Trap
A few adult codling moths can be drowned in homemade vinegar traps. These are constructed from one-quart plastic milk jugs with holes cut through two opposite sides. It takes quite a few — at least two per tree — and the vinegar solution must be replaced every week or two, so this is a labor-intensive technique for the backyard gardener. Here is the recipe for the vinegar solution, which is enough for two dozen trees: