Managing Codling Moth in Montana Home Orchards
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.
For home plantings and orchards, several cultural and mechanical control measures are available to prevent damage to a harvestable crop of fruit, if implemented properly. Any spray controls should be applied following the product's label with proper equipment and rates as well as timing based on the insect's life cycle.
Description & Life Cycle
As temperatures rise above 50°F in the spring, the first generation of moths emerge, mates, and begins laying eggs on immature fruits or nearby leaves. Adults are ½ inch grayish-brown moths with a dark copper-colored band at wing tips (photo above). Eggs hatch into larvae (caterpillars/“worms”), which are ¼ to ½ inch long with cream- to pink-colored bodies and black or brown heads (photo above). Larvae feed on leaves, 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. Moths overwinter as larvae by spinning cocoons located 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.
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.
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. Timing of mechanical controls such as banding and bagging as well as chemical controls are dependent on the life stage of the moth which is driven by temperature. 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. 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 by 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 square on the map below to view biofix for 2020. Data for other locations will be added as it is available. See also the 2019 map below for last year's biofix and suggested larvicide spray dates.
2019 Biofix and Spray Dates
Orchard sanitation and fruit thinning
Keeping your orchard floor free of dropped fruit and removing codling moth damaged fruit from your tree(s) 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. To thin fruit, simply remove all but 1-2 of the largest fruit from clusters when the fruit are about marble size. Fruit clusters should be spaced about 6 inches apart, and fruit within clusters should not be touching to help reduce codling moth damage. Fruit thinning will also discourage trees from cropping heavily one year and not a all the next, or biennial bearing.
Initial trapping of moths with pheremone lures to determine biofix is an important management tool, however, trapping moths with other lures typically does not provide adequate control to reduce populations or result in fewer damaged fruits. Moth traps or bug zappers are usually most effective in situations where a single isolated tree can be managed for codling moth. If other fruit trees exist on neighboring property, trapping is largely ineffective.
Fruit bagging can prevent individual fruits from damage and is appropriate for home growers hoping to harvest a small crop for storage or fresh eating. Bagging should occur after fruit has been thinned and can be done until fruit is about 1" in diameter. Fruit bagging is an inexpensive control measure that WARC tested on apples in 2019. Fruit can be bagged with paper bags, panty hose or plastic baggies; however, WARC has found the latter—while effective for preventing codling moth—created a moist environment attractive to earwigs. In future studies, alternative bagging materials will be tested.
Trunk banding, with strips of corrugated cardboard, can be used to capture pupated larvae and remove them from the orchard. Efficacy of this control is based on proper removal and disposal of bands which must be timed with the development of each generation of moths. It is appropriate to use as one of several non-chemical measures to reduce overall codling moth pressure and is most effective for trees with smoother bark. It is also an option in large trees where home spraying is difficult.
To maximize trapping of pupae, bands should be placed on trees coinciding with initial egg hatch (220 DD from biofix) and replaced with new bands prior to emergence of the next generation of moths approximately once a month. Final bands should remain on trees until the final generation has pupated about the time fruit is harvested. All bands should be burned or disposed of offsite to prevent reinfestation.
Promotion of beneficial insects and natural predators
Several natural predators of codling moth exist including birds, bats and beneficial insects like assassin bugs, parasitic wasps and lacewing larvae (CSU Codling Moth in Home Plantings). Encouraging habitat for birds and bats in your landscape can be helpful to keeping populations in balance (Intermountain Fruit Production Guide--Birds and Bats for Pest Suppression). While the release of Trichogramma wasps and nematodes has been suggested to reduce codling moth pressure, the efficacy of these predators on codling moth control has not been tested in home plantings and should be considered experimental.
Insecticide controls targeting larvae are always applied after petal fall and should never be applied during bloom when risk to harming pollinators is high.
For home growers chemicals should be used as a last result and with proper application equipment. Both organic and conventional options for controling codling moth are available for home growers. Spray controls can target various life cycle stages of the moth. For example, horticultural oil, which is used to smother eggs, must be timed prior to egg hatch. Other sprays target larvae and must be applied to coincide with egg hatch.
Some of the organic options include the active ingredients spinosad, Bacillus thuringiensis var kurstaki (or Btk), kaolin clay, horticultural oil, and the codling moth granulovirus (CpGV or Cyd-X). Conventional controls include the active ingredients carbaryl, malathion and permethrin. Any chemical spray program should not rely on any one chemical control so as not to cause pest 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 timed sprays for maximum control of larvae. Please consult your local Extension office if you have questions about applying chemicals to your trees.
For More Information
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 Plantingsand UC Davis's publication, How to Manage Pests in Gardens and Landscapes 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.