How can I control codling moth in apples?
Answer: The codling moth, Cydia pomonella, is present throughout North American apple-growing regions. Prior to the advent of synthetic pesticides, the codling moth larva was the proverbial “worm in the apple.” Relatively cold regions may have only one generation of the codling moth, while in the warmest apple-growing areas the codling moth may pass through two to three generations per season. Several organically acceptable controls are available and discussed below.
Among the most effective nontoxic controls for codling moth is mating disruption using pheromones—chemicals naturally produced by insects as a means of communication. During the mating period, female codling moths release pheromones that signal their locations to males. By releasing quantities of these pheromones into the orchard, the grower can confuse and disrupt the moth’s mating cycle. This approach faces two general problems: difficulties with sustaining an even, long-lasting distribution of pheromones throughout the orchard and complications due to the biology and initial distribution of the codling moth. For instance, dispensers can release pheromones too slowly or too quickly, thus allowing mating to occur. Orchard layout is another consideration. For best results, trees should be evenly spaced and of equal heights since treeless spaces and taller trees interrupt the pheromone spread. Cold weather can cause too little pheromone release and hot weather can cause the pheromone to deplete too fast. Since the pheromones actually attract male moths, fruit damage can be worse if pheromone levels drop low enough to allow mating to occur (Quarles, 1994).
Dispensers should be placed as high in the trees as possible, since mating can occur in the air above the dispensers. For pheromone dispensers to be effective, it is important to use them at the recommended rate per acre (Warner, 1996). An aerosol dispenser, nicknamed the “puffer,” which uses a timer to periodically spray pheromone into the orchard air, is an effective dispensing method. These puffers reduce the labor requirement of tying pheromone twist-ties on to orchard trees. Some of the puffers are allowable for use by the USDA National Organic Program.
For organic growers it will probably not be feasible to achieve adequate suppression using mating disruption alone. Growers in California have significantly improved codling moth control by combining mating disruption with black-light traps. Both male and female codling moths are strongly attracted to black light (Howell, 1997).
Prior to the development of the mating-disruption system, pheromones were used primarily for monitoring to determine the best timing for spray applications. Degree-day monitoring can also be used to this effect. Since insects are cold blooded, weather monitoring can forecast when an event, such as egg hatch, will occur. This information can be obtained by calculating degree days and can be used to implement control methods, such as pesticide applications or cultural manipulations, so that they are used at the most effective time in the pest’s life cycle.
There are several “windows” in the pest’s development that, if detected, can greatly increase the effectiveness of control measures. Determination of these critical periods is especially important, since codling moth eggs are fairly resistant to pesticide treatments, and once the eggs hatch, the larvae will quickly enter a fruit and be protected from sprays. While Bacillus thuringiensis has shown effectiveness with other moth pests, it is not as effective on codling moth, and additionally can be cost prohibitive. A granulosis virus, originally identified from codling moth, has been shown to be effective for control of early-stage codling moth larvae. This virus was developed for commercial use in Europe and has been used in the United States under the brand name Cyd-X (CMISS, 1998). Degree-day monitoring is necessary to time the application of Cyd-X.
The trichogramma wasp is increasingly used in U.S. orchards as a biological control organ¬ism against codling moth. The wasps can be ordered from insectaries, which ship them as pupae inside parasitized grain moth eggs glued to perforated cards (100,000 trichogramma per card). Each card can be broken into 30 squares, allowing for even distribution in orchards and fields. Trichogramma parasitize freshly deposited moth eggs, so release of the adult wasps should be timed to coincide with moth egg-laying. Degree-day monitoring can help determine when egg laying is occurring. Trichogramma feed on insect eggs, nectar, pollen, and honeydew. They live much longer and destroy more codling moths when supplied with nectar. Good nectar and pollen sources in and around the orchard, such as borders or strips of unsprayed alfalfa, sorghum, sunflower, corn, clovers, and wildflowers, will increase Trichogramma parasitism of pest eggs. Beneficial organisms are not sufficient by themselves to affect a commercially acceptable level of control; rather, they play a potentially potent part in an overall long-range ecological management strategy. Best results are usually observed after three to five years of releases, as the population of beneficials grows.
Sanitation and cultural practices can help reduce codling moth populations. Woodpiles, boxes, and bins can be a major source of reinfestation, so these should be kept away from the orchard. If wooden crates or boxes are discovered to contain codling moth pupal cases, they can be disinfested by scorching with a propane torch.
In smaller orchards, codling moth larvae can also be intercepted as they descend the trunk to pupate in bark crevices, soil, and certain weed stems. Wrap the trunks with corrugated cardboard, which will provide an attractive artificial pupation site. In areas with only one generation of codling moth, remove and burn the cardboard at the end of the season. If there are two or more generations, the cardboard should be removed and destroyed about a month after the first larvae moved down to pupate. To determine the timing of this larval movement, use the degree-day method described above or employ a trap of a 6-inch-wide burlap strip painted with Tanglefoot and wrapped around the trunk just above the cardboard wraps (Dickey, 2009).
You can learn much more about apple pests in the ATTRA publication Apples: Organic Production Guide. This publication provides information on organic apple production from recent research and producer experience. Many aspects of apple production are the same whether the grower uses low-spray, organic, or conventional management. Accordingly, this publication focuses on the aspects that differ from nonorganic practices—primarily pest and disease control, marketing, and economics.
Note: The mention of specific brand names, manufacturers, or companies is for educational purposes only and does not constitute endorsement by ATTRA, NCAT, or USDA.
Codling Moth Information Support System (CMISS). 1998. Integrated Codling Moth Management Biological Control of Codling Moth. Oregon State University. www.ipmnet.org
Dickey, Philip. Coddling Moth. IPMopedia. IPM Education Project. Sponsored by Toxipedia.org.
Howell, J.F. 1997. Organic orchard assistance. The Grower. June. p. 14-15.
Quarles, William. 1994. Mating disruption for codling moth control. The IPM Practitioner. May/June.
Warner, Geraldine. 1996. Number of dispensers is key to mating disruption. Good Fruit Grower. Vol. 47. No. 6. p. 16-18.