By Patrick Mangan, MSU Extension Agent, Ravalli County
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. Data combining the presence of adult codling moths and ambient air temperatures have been programed into a modeling program to help us predict the beginning of the larvae hatch this spring. The model predicts the hatch would begin on June 5th this year. Begin the first application of control sprays around June 9th.
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. The developing codling moth eggs have a temperature “sweet spot” they like to be at, within the range of 50 to 88 degrees Fahrenheit. If the ambient air temperatures are too cold, the eggs won’t develop for that period of time. Additionally, if the air temperature is above 88 degrees Fahrenheit, the development of the larvae will halt, and even degrade a little. After a confirmed biofix, the model accumulates degrees of temperature and time length in that sweet spot between 50 and 88 degrees. The accumulation of the total degrees of temperature are known as degree days. As the eggs reach 250 degree days, they are expected to begin hatching as larvae. The hatch rate moves from a 1% hatch rate at 250 degree days to a 3% hatch rate at 340 degree days. For this year, the model predicts a 1% hatch on June 5th, and 3% on June 9th.
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.
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.