Time for apple and pear orchardists, both backyard hobbyists and larger commercial growers to begin applying control sprays for codling moth in apples and pears.
The modeling algorithm and temperature data used to predict codling moth activity predicts the beginning of the larvae hatch to be on or near June 13.
Every spring, orchardists and researchers hang pheromone traps in their apple trees to attract the emerging adults as they mate and lay eggs. The presence of the first adults in the traps is documented as “the biofix,” and starts the temperature based model.
As the spring progresses, the eggs develop into larvae. The development time for the larvae is impacted by the ambient air temperature. A computer model calculates when the larvae will begin to hatch based off of temperature data gathered at weather monitoring stations.
The timing of spray applications while the larvae are hatching is important to the control. For contact types of sprays to be successful, they must be applied when the larvae are present and outside of the apples. If sprays are applied too early, then they may lose viability for control before the hatch is over, requiring additional applications. If the spray application is too late, then larvae have already burrowed into the apples and are out of reach of the control mechanism.
There are a host of spray control options for codling moth larvae. Organically derived sprays include Spinosad or pyrethrin.
Conventional insecticide options include malathion, carbaryl, or permethrin. It is important to read and follow all directions found on the label of the product you choose and understand the persistence and viability of the spray.
Many products will require multiple applications during the hatching period to get the desired amount of control on codling moth and wormy apples. Read the label completely and understand the interval for reapplication to ensure the best control of codling moths and wormy apples.
It is important to note that the dates of codling moth and the larval hatch can vary from place to place in mountain environments like the Bitterroot valley up to a month. The development of the eggs and larvae depend on the air temperature.
The models we use draw data from weather stations in Stevensville and Corvallis. But colder areas may have delayed development of the larvae and the flowering of the trees. It is very important to note that we should not spray trees that are flowering, which can lead to injury to our pollinator populations.
Individuals can search for sign of codling moth larvae on their own fruit. Inspect fruit often for the first sign of “stings,” or entry sites on fruit from the first codling moths. Stings are very small reddish-brown piles of frass, about 1/16th of an inch in diameter. You might be able to see the tiny entry hole where the larvae entered the apple if you scrap away the frass.
There are numerous integrated pest management strategies that can be employed to aid in the management and reduction of codling moths. Removal of fallen apples each fall can help, as can strategic thinning of the fruit on the tree at clusters where they touch each other.
Encouraging the presence of bats, predatory wasps and some birds can also help. Wrapping the trunks of trees with corrugated cardboard can also intercept the pupating larvae, for eventual removal prior to the emergence of adults in the following spring. There are additional biologic controls including viral controls and pheromone lure traps for mating disruption that can be considered.
The MSU Extension Office and MSU Western Agricultural Research Station work together closely to monitor for adult codling moths and the collection of weather and temperature data. The MSU Extension office in Hamilton coordinates an automated phone call and email as the beginning of the spray window arrives each spring. Call the office at 406-375-6611 to be added to the list for future notifications.