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What is a codling moth?
Codling moths are small gray and brown insects considered to be the greatest threat to many fruit and nut growers. Their primary targets are apples and pears, but they have also been known to attack English and black walnuts, plums, and quince, a fruit used in jellies, preserves and pies.
Codling moths spend the winter primarily under loose bark as mature larvae in a silken cocoon. In some areas, they emerge as adults in the spring, starting in mid-March, but later generations emerge from June through September, depending on the area and the crop.
The earliest codling moths land on the leaves and spurs of fruit trees, where they lay eggs. The eggs then hatch into small larvae that may chew into the leaves, but mainly move to the fruit. Later generations lay eggs directly on the fruit. After exiting the fruit, the larvae crawl down the side of the tree under loose bark, develop into cocoons, and the process begins all over again. The codling moth produces two to three generations each year.
What types of damage can the codling moth do?According to the United States Department of Agriculture (USDA), if left unchecked, the codling moth has the potential to destroy 80 percent of the apple crop in the Northwest and 50 percent of the pear crop. The destruction is caused by larvae that tunnel into the core of the fruit, expand the seed cavity, then eat the seeds, making the fruit unfit for human consumption. That means reduced profits for growers and fruit packinghouses.
The larvae will often leave a mass of chewed material or excrement outside the entrance known as "frass." Some pieces of fruit may have more than one entrance hole with each one surrounded by frass.
The larvae may also cause another type of injury known as a "sting." A sting is a place where the larvae chewed just a small amount, then either died inside the fruit or entered at another place.
What steps can be taken to reduce codling moth damage?
There are some non-chemical methods that can be used to control the codling moth so that damage to fruit crops is minimal. One is called "mating disruption." This involves the use of dispensers containing pheromone, a synthetic copy of a scent emitted by female moths to lure males when they are in the mood to breed. Males that are attracted to the pheromone scent become confused when they can't find their female companions and fly away. This means the female moths are unable to lay the eggs that ultimately lead to damage.
One type of mating disruption dispenser in use in orchards in California is called the "puffer." This brown rectangular box emits pheromone equal to the scent of seven to 10 million female months into the air every 15 minutes.
You can also control the spread of larvae by immediately removing fruit containing worms from your trees and picking up infested fruit that has fallen to the ground. Fallen fruit should be buried underground six to 12 inches or placed in a black plastic bag in the sun for at least four weeks before it can be used as compost.
Wrapping burlap or corrugated cardboard collars around the tree trunks and main scaffolding branches may also help prevent the development of larvae within the tree bark. Place a 3- to 4 inch wide piece of cardboard around the trunk 12 to 18 inches off the ground and secure it with plastic flagging tape, string, or wire that can be removed or retied. A burlap bag can also be used. Mature codling moth larvae are attracted to these collars and try to use them to spin cocoons. The collars are usually more effective on trees with smooth bark, as opposed to trees with rough bark that provide the larvae more places to pupate. Be sure to check the collars frequently in early June through September for larvae that may be starting to develop.
Try to limit the use of pesticides to control codling moth. Some chemicals may kill beneficial insects, such as wasps, spiders and predatory bugs that prey on codling moth. Always use traps for monitoring and degree-day models before deciding if and when to spray.