Codling moth decimates local apple crops

Codling moth can devastate an apple, pear or walnut crop.

In Medicine Hat this summer, many apple trees in the city lost their entire crop. Gerry Prince, a resident of the city, said via email, “Everyone I know on the south side of town had problems and had to throw most of their apples away.”

While Prince normally has a great apple crop, this year almost all of them went into his green bin, filling it more than half full. He requested some advice on how to protect the apples next year.

Codling moths overwinter in silken cocoons which are either under loose bark or at the base of the tree in the soil or under debris. They emerge as adult moths in early spring. Following mating, females will lay eggs on the apples, where the young bore into the fruit once they hatch. Once fully developed, the caterpillars drop from the fruit, spin a cocoon and start the cycle over again.

Once populations are high, they are more difficult to manage by natural controls and pesticides might need to be employed as well to get the population back under control. If using natural methods, it is best to use several at the same time to see any effect.

Natural methods of managing moths include thinning the fruit when they are small, ensuring to pick any that have small holes in them made by codling moth caterpillars. Composting alone doesn’t kill the caterpillars. It is recommended to put affected fruit in a thick black garbage bag, seal it tightly and put it in a sunny spot for a month before composting.

Thinning the fruit to one apple per cluster is advised to keep the tree vigorous. Apples that drop off the tree should be picked up and also put in a garbage bag in case they are harbouring caterpillars.

There are traps which can be used for both the moths and caterpillars, and bagging fruit is recommended.

For more detailed advice see either https://www.pesticide.org/moths_codling or http://ipm.ucanr.edu/ under home, gardens, landscapes and turf, and then codling moth.

SAMANTHA JOHNSON, Local Journalism Initiative Reporter, Medicine Hat News