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Gardening Articles: Care :: Pests & Problems

Healthy Home Orchards (page 2 of 5)

by Whitney Cranshaw

Codling Moth

No discussion of fruit-loving insects can avoid the codling moth (Cydia pomonella), the proverbial "worm" in the wormy apple or pear. Larvae tunnel into the fruit in search of its nutritious core, but in doing so, they destroy the flesh of the fruit that we cherish. Codling moths start the season within a silken cocoon, hidden in and around fruit trees.

The following spring, the first adult moths emerge, usually around the time of full bloom. Over the next few weeks, female moths lay eggs on the leaves and young fruit. Some of the newly-hatched caterpillars manage to make it into the developing fruit, although few are successful.

However, it's the second generation of the moth that worries apple and pear growers. This generation typically occurs in mid to late July. Eggs are laid directly on the fruit. One to two weeks later, eggs hatch and the young larvae tunnel into the fruit, usually at the calyx end or where two fruit touch--both sites offer these tiny insects a better grip as they try to cut through the fruit's skin.

Codling moth control usually involves repeated use of insecticides, so that plants are protected during the entire egg-laying period. If the activity of the moths is monitored--by the use of attractant pheromone traps, for example--then use of sprays can be limited to only those periods when the moths are most active. Otherwise, use a regular 10- to 14-day schedule of sprays, beginning as soon as flower petals fall, to ensure a near worm-free crop.

Sprays of the insecticide Bacillus thuringiensis (Bt) are moderately effective. Sprays of kaolin clay are also promising. At least three sprayings are needed, and timing is critical: Make the first spray 15 days after petal fall begins, and subsequently at 5-day intervals.

Many gardeners don't want to go through such a hassle and are willing to give up a few fruit to the caterpillars in return for cutting back on insecticide sprays. Several cultural controls can assist them in this regard.

Trap larvae. After larvae have finished feeding on the fruit, they wander to flaps of bark or other protected sites to pupate. Assist them in this by providing an "artificial bark flap", such as a band of corrugated cardboard or burlap, on the trunk. The caterpillars will use the band as a "resting" site to complete pupation. There they can be collected and destroyed.

Make sure that the bands are checked at least every two weeks, or the codling moth caterpillars may transform to the adult moths and escape before you get to them.

Trap the adults. Adults of both sexes can be attracted to fermenting mixtures and then trapped. Mix some molasses in water (about a 1 to 7 ratio is frequently suggested) and pour it into a cut plastic milk jug or other homemade trap and hang it on the tree.

(Note: Pheromone traps contain the sex attractant used by the female to attract male moths. They are highly effective in this regard but, unfortunately, trapping male insects doesn't do much in terms of population control. Instead the remaining males become more sexually active and females end up producing just as many little ones.)

Thin fruit. Thinning is often a desirable practice in promoting larger fruit and steadier production. It also controls codling moths. Young caterpillars have great difficulty holding on as they cut into the fruit. Areas where two fruit touch provide them leverage, but their success in tunneling is even more limited once these sites are removed.

Biological controls. Codling moths are attacked by several natural enemies, although these rarely are effective enough to prevent serious crop damage. Releasing additional natural enemies helps. Trichogramma wasps, tiny parasites of the moth's egg stage, are commonly reared by insectaries and sold for pest control. If you're trying out trichogramma, release them when there is evidence of codling moth eggs. Consider sequential releases at one to two week intervals throughout the egg-laying period. This can usually be easily arranged with your supplier.

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