Managing Codling Moth in Montana
Photo 1. Adult male moth showing copper bands (Wikimedia Commons).
Description and Life Cycle:
Commonly referred to as “the worm in my apple,” codling moths are the primary insect pest of apple and pear in Montana. Adults are ½ inch grayish brown moths with a dark copper colored band at wing tips (Photo 1). Larvae are ¼ to ½ inch long with cream to pink bodies and black or brown heads (pictured above). Codling moths overwinter as pupa in tree bark cracks and soil near trees. As temperatures warm in the spring (above 50°F), adults emerge, mate and begin laying eggs near fruit sites on trees. After eggs hatch, larvae feed on leaves, shoots, and later burrow into fruit until they pupate to emerge again as adults. Depending on temperatures, there can be up to three generations of codling moths in Montana per growing season.
Photo 2. Codling moth larvae in apple (Wikicommons media). Photo 3. Moths in trap used to determine biofix (Zach Miller).
The initial emergence of codling moth in spring, referred to as biofix, involves the capture of male moths in pheromone traps (Photo 3). It is determined based on the date when at least two moths have been caught in a trap on two consecutive nights (Alston, et al. 2010). Biofix helps growers time chemical controls to target larvae, the stage of the insect harmful to apples. Chemical controls are always applied after petal fall and should never be applied during bloom when risk to harming pollinators is high.
Biofix varies across the state depending mostly on temperature. Dates for 2018 biofix in several locations around Montana are displayed in the map below. Additional biofix and estimated spray dates will be added in Table 1 below for the 2019 season as they become available for locations across the state. Biofix has been monitored in Corvallis, MT at the Western Agricultural Research Center since 1991. Biofix dates have ranged from May 6 to June 3 at this location with most dates falling around the second or third week of May.
You can contact your local Extension agent using this directory for help determing biofix and subsequently spray dates. You can also determine biofix for your exact location by hanging pheremone traps in your apple trees during the beginning of bloom, usually starting around the first week of May for Zones 5 and 6 and the second week of May for Zones 4 or lower. Traps, are not a control measure but simply provide information on when moths emerge and help determine the most effective spray date for applying chemicals (see chemical controls). Traps should be checked daily for male codling moths. Be aware codling moths can look similar to sage moths, another native moth emerging around the same time. For more information on correctly identifying codling moths and distinguishing them from sage moths visit WSU's resource Early Season Codling Moth Monitoring. For more information on setting traps and determining biofix refer to Utah State University's Pest Fact Sheet, "Codling Moth (Cydia pomonella)."
2019 Biofix and Spray Dates
|Location||Biofix Date||Larivicide Spray Date|
|Big Timber, MT||6/4/19||6/28/19|
|Bridger, MT||No Data||No Data|
|Colstrip||No Data||No Data|
|Hinsdale||No Data||No Data|
|Fort Belknap||No Data||No Data|
|Great Falls, MT||05/17/19||6/24/19|
|Miles City, MT||5/13/19||6/15/19|
|Red, Lodge, MT||No Data||No Data|
|Whitehall||No Data||No Data|
|Winston, MT||No Data||No Data|
Table 1. 2019 biofix and spray dates. The table will be updated as information becomes available. Spray dates will be based on degree days from biofix and will be reported for first chemical spray targeting emergence of first generation of codling moth larvae. See control for more details on control options and degree day calculations.
2019 Codling Moth Damage Survey
In August 2019, WARC personnel assessed codling moth damage at orchards statewide where no codling moth management had been attempted. Where possible 20 fruit from 20 trees were assessed for the presence of codling moth damage. Apple varieties, age, and yield varied according to site; for more details contact us. In general, there appears to be be higher rates of codling moth damage west of the continental divide.
Mechanical and Cultural Control:
There are several options for managing codling moth in backyard plantings. Homeowners should start by practicing good sanitation by picking up and disposing of dropped fruit. Fruit should not be composted as home compost piles may not reach sufficient temperatures to kill pupa. Trees can be wrapped in corrugated cardboard or tree bands covered with Tanglefoot to trap pupating larvae. Wraps should be applied in late summer and removed and destroyed before adults emerge in the spring. In small plantings individual fruits can be protected by wrapping fruit in panty hose soon after fruit begins to set. Thinning fruit is also helpful in reducing damage as larvae will burrow between touching fruit. Codling moth mating disruption dispensers are available, but these work optimally with areas of 10 acres or greater. For more information on using mating disruption read Utah State Univeristy's Pest Fact Sheet, "Codling Moth Mating Disruption."
Several chemical controls are available. Some of the organic options include the active ingredients spinosad, Bacillus thuringiensis var kurstaki (or Btk). Other organic options include Kaolin clay, horticultural oil, and the codling moth granulovirus (CpGV or Cyd-X). Conventional controls include the active ingredients carbaryl, malathion and permethrin. A full list of chemicals registered in Montana for commercial use as well as a cost estimator are available in this downloadable spreadsheet. Additionally, any spray program should use some combination of controls so as not to cause tolerance of a certain chemical and to control insects at various stages. For example, WSU delayed first cover approach uses horticultural oil to smother eggs followed by chemical sprays to reduce egg hatch and time sprays for maximum control of larvae.
The timing of chemical controls is based on the degree days accumulated from biofix to target the greatest period of egg hatch. Degree days are calculated by monitoring for biofix and using an equation based on cold-blooded insects development being dependent on temperatures rather than day length or date. Biofix and egg hatch vary greatly from site to site as temperatures can vary greatly between different areas especially in mountainous microclimates. Table 2 below provides various insect development stages based on degree day accumulations from biofix. Be careful to note when reading any recommendations to note if degree days are reported from biofix or January 1 (WSU uses the later).
After the first spray is applied according to the degree day accumulations from biofix, subsequent sprays should be applied according to the label of the chemical chosen. Strategic timing of the first spray to target the first generation of moths is critical to control. You can use a nearby weather station to calculate degree days and estimate emergence using the calculator provided as part of USpest.org located here or if you are located near Corvallis, Stevensville, Bozeman, Miles City, Columbus or Helena, MT you can use the Utah TRAPS tool to track degree days and time controls. Links to each of these stations is provided on our weather data page listed under producer resources.
Table 2. Codling moth development activities. Source: http://www.intermountainfruit.org/insect-biology/codling-moth
For more information on identification, life cycle and management of codling moth in backyard plantings visit Colorado State University’s publication Codling Moth: Control in Home Plantings.
Disclaimer: These recommendations are provided only as a guide. It is always the pesticide applicator’s responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned. The authors and Montana State University assume no liability resulting from the use of these recommendations.