Managing Codling Moth in Montana Commercial Orchards
Photo 1. Adult male moth showing copper bands (Wikimedia Commons).
The "Worm in Your Apple"
Codling moths are the primary insect pest of apple and pear trees in Montana and can destroy an entire crop if uncontrolled. Understanding the moth's life cycle is important for determining management methods and timing of controls. Depending on temperatures, there can be up to three generations of codling moths in Montana per growing season. Control measures implemented with the first generation will be most effective and efficient for preventing crop damage by reducing codling moth populations and protecting fruit from damaging larvae. Following is information regarding controlling the moth in commercial plantings (orchards of one acre or more). For management techniques suitable for home growers please visit Managing Codling Moth in Montana Home Orchards.
Description and Life Cycle:
Photo 2. Codling moth larvae in apple (Wikicommons media). Photo 3. Moths in trap used to determine biofix (Zach Miller).
As temperatures rise above 50°F in the spring, the first generation of moths emerges, mates, and begins laying eggs on immature fruits or nearby leaves. Adults are ½" grayish-brown moths with a dark copper-colored band at wing tips (photo above). Eggs hatch into larvae (caterpillars/“worms”), which are ¼-½" long with cream- to pink-colored bodies and black or brown heads (photo above). Larvae feed on leaves and shoots and later burrow into fruit to feed on the developing seeds. After they are fully grown (1/2” - 3/4”), larvae will emerge from the fruit, seek a protected site to pupate (form a chrysalis-like structure), and transform into the next generation of moths. In the fall, larvae spin cocoons for overwintering in loose bark, soil, and debris near the base of the fruit trees. In early spring, larvae become pupae for their transformation into adult moths.
Timing and efficacy of various controls depend on insect life cycle which is dependent on temperatures as described below.
Timing of Controls
|codling moth pheremone trap
photo by Zach Miller
Biofix & Degree Day Calculations
Management of codling moth must be timed appropriately for safety and efficacy. In Montana, biofix, or the date of initial emergence of the moths in spring, is used to determine timing of controls based on subsequent degree day calculations. Chemical controls for codling moth are always applied after petal fall and should never be applied during bloom when risk to harming pollinators is high.
Biofix is determined based on the date when at least two male moths have been caught in a pheromone (sexual attractant) trap on two consecutive nights (Alston, et al. 2010). A degree day is any day that the temperature rises one degree above the threshold temperature at which no development of that particular insect pest can occur. In the case of codling moth, that threshold temperature is 50°F/10°C degrees.
Other regions rely on models calculating degree days from January 1 or March 1 to predict moth emergence and development to determine control timing. Currently, MSU researchers at WARC are working to determine if these same models can appropriately predict codling moth in our mountainous region. Be careful to note when reading any recommendations whether degree days are calculated using biofix, January 1, or March 1.
Monitoring Codling Moth Using Pheremone Traps in Montana Orchards
Codling moths usually start appearing around the first week of May for Zones 5 and 6 and the second week of May for Zones 4 or lower (find your plant hardiness zone here). Biofix and egg hatch dates vary greatly with temperatures at different sites, especially in mountainous microclimates. Dates for 2019 biofix in several locations around Montana are displayed on the map below. Some Extension offices can provide you with biofix information, however, you can also purchase pheremones and orange delta traps online from various suppliers including Gemplers and Arbico Organics to determine biofix at your specific location. Note that these traps are not a control measure but simply provide information on when moths emerge and clues about codling moth pressure in your orchard. Traps should be hung at the beginning of bloom (at the pink stage) in the upper canopy of trees perpendicular to prevailing winds.
Once you catch two moths on two consecutive nights, you have determined biofix and can begin calculating degree days to inform your management decisions. You can use a nearby weather station to calculate degree days and estimate emergence using the calculator provided as part of USpest.org. 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. Please contact your local Extension agent using this directory for help determining spray dates for the current year.
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)".
2020 Biofix and Spray Dates
In Montana, spray dates are based on degree days from biofix and are reported for first chemical spray targeting emergence of first generation of codling moth larvae. Note that suggested spray dates may vary from year to year, and this table will be updated with new information as it is available. Strategic timing of the initial spray to target the first generation of moths is critical to control. After the first spray is applied according to the degree day accumulations, subsequent sprays should be applied according to the label of the chemical chosen.
Click on any orange dot on the map below to view 2020 biofix. More dates will be added as they become available. See also the 2019 map below for last year's biofix and suggested larvicide spray dates.
2019 Biofix and Spray Dates
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. Growers should determine their threshold for codling moth damage and manage for the insect accordingly. WSU's Codling Moth webpage provides guidelines for determining treatment thresholds based on monitoring adult moths through the growing season.
Table 1. 2019 Codling moth damage survey
Orchard sanitation and fruit thinning
Keeping your orchard floor free of dropped fruit and removing codling moth damaged fruit from your trees throughout the season can reduce overall crop damage. Fruit should be inspected for holes with frass (excrement and other waste associated with insect activity) indicating the presence of larvae. Damaged fruit should be removed and destroyed. Early removal of damaged fruit will reduce future generations of codling moth and overall damage to fruit including secondary damage from wasps and birds.
Fruit thinning is a common orchard practice that produces larger, high-quality fruit and also prevents codling moth larvae from migrating between fruit. For commercial growers, fruit thinning and crop load management will depend on tree age and the cultivar of fruit being grown, however, as a general rule fruit should be thinned to 1-2 fruit every 6" with no fruit touching. Fruit thinning will also discourage trees from cropping heavily one year and not a all the next, or biennial bearing. For more on thinning fruit visit WSU's list of resources on crop load management.
Codling moth mating disruption dispensers are also available and used by some Montana orchards, but these work optimally with areas of 10 acres or greater. For more information on using mating disruption read Utah State University'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 if degree days are reported from biofix, January 1, or March 1.
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 by USpest.org, 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
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.