by Timothy J. Smith
Codling Moth has been the key insect pest of apples in Washington since the early 1900’s. Damage was constant and, despite heavy spraying with lead-arsenate, 10-25 percent losses were expected yearly in orchards up until 1948, when DDT became available to growers. Control has been relatively easy since that time, with azinphos-methyl (Guthion) becoming the standard control material from 1965 until present. This azinphos era is rapidly closing, as new control methods and materials evolve.
For 30 years, loss of control of this insect has been considered a sign of carelessness on the part of the grower and their advisers. Since the mid-1990’s, the background population of codling moth in Washington apple growing regions has been increasing, and partial loss of control is a more frequent occurrence. Control breakdowns now lead to significant economic damage, rather than mild embarrassment.
Adoption of new control strategies is accelerating, as growers are beginning to realize the older “easy” management methods are becoming less reliable in high pressure regions. Recent demonstrations of the use of pheromone confusion (supplemented by traditional sprays) in large contiguous blocks has reassured growers that the newly developed method works, though this method remains more expensive than presently available effective products. This pest remains one of the more difficult to manage with newer lower-toxicity control products, such as the insect growth regulators, due to adult and larval behavior that differs significantly from many other Lepidoptera pests. Unlike most in this genus, the larvae of Codling Moth does not consume leaves or fruit surface tissue. To be effective, an insecticide must have contact action on the adult, egg or very young larva in the few hours it remains on the foliage or fruit surface. Research shows promise of possible new control products.
In Washington, this insect has from 2 to 3 generations per year, depending on the warmth of the growing region and the relative warmth of the growing season. Adults first emerge about 14-30 days after bloom, the first significant flight an mating taking place when evening temperatures exceed about 60 degrees F. This first significant flight and mating is identified by trap monitoring, and is documented as “biofix” in the temperature driven codling moth model. First generation continues for about seven to eight weeks, until late June or early July. The second generation takes place during July and the first 2 or 3 weeks of August. (Chart) It is individuals from the later portion of the second generation that enter diapause to overwinter in the orchard, though it seems that some of the first generation larvae may emerge the next spring, too.. A partial third generation often extends into early October, as an ever-decreasing number of the second generation mature into adults. Damage is common after September, especially when moth numbers are high, and the weather stays warmer than normal.
Males fly relatively well to find females, usually up to about 1/4 mile (400 meters). The males can move much farther, at times caught more than a mile from their point of release. Females do not often fly far, generally a few hundred feet or less if there are hosts nearby. Females attract males by releasing a pheromone. A synthetic codling moth pheromone is used in traps to detect the presence of males, and to roughly estimate the numbers of females present in the area. Females may lay over 100 eggs, mostly on or near fruit. Eggs hatch 8-14 days after they are deposited on the surface. Larvae must find and enter fruit within a few hours of hatching. They enter either through the skin or the calyx, and though they may chew their way into the fruit, they do not swallow the surface layer.
Most newly hatched larvae fail to live long enough to penetrate fruit. Larvae are most successful when weather is warm and dry. Larvae from the eggs of a single female can damage 20 to 60 fruit. Surface damage to the fruit skin caused by larvae that died soon after penetrating the skin is called a “sting” by growers. Any codling moth damaged fruit is discarded during sorting in the packing house.
Once inside the fruit, the larvae remain near the surface for 2-4 days, then penetrate to the core, where they feed on seeds and flesh for 3-4 weeks. When fully grown, the larvae leave the fruit, find sheltered places on or near the host tree, and spin a shelter. At this point, they may either remain dormant for the winter, or emerge after 2-3 weeks to further infest fruit.
The first codling moth generation is generally the lowest in potential numbers, is struggling to survive in cooler, wetter Spring weather, and is easiest to contact by sprays. Successful codling moth control is dependent on proper timing of effective management programs or materials in the entire neighborhood during this first generation. Loss of control at this time usually leads to greatly increased damage (see image at right) during the remainder of the growing season.
The development of the codling moth generations is modeled and reported by web sites to the growers and their advisers. Many advisers share the timing of their first trap catches, pooling their data for more accurate “biofix” dates for the region. Most growers time their control programs based on the progression of the codling moth phenology model.
Application of spray materials has traditionally started when models indicate that 3% egg hatch has been reached. With the advent of new control materials and strategies, this application starting time may be moved forward a few days to 100 degree days after biofix, to affect the first egg deposition. Sprays are applied to maintain coverage during the entire first generation, which may last from about 50 to 65 days, depending on local temperatures. This once required two sprays (first and second cover), but those days seem long gone with current products. Many growers are now asked to apply three covers for 1st generation, timed to be at their freshest during rapid egg hatch periods.
The development of the second generation usually begins in late June to early July, and if trap catch data or past history indicates that this generation presents a problem, the grower may choose to apply control materials during the six weeks that this generation continues. Number of sprays depends upon the products used and the relative numbers of codling moth that are present in the area. This second generation is often much more successful, as trees are more difficult to cover with protectents, and the weather is usually warm and dry, which is what the codling moth prefer. Growers seldom spray the partial third generation that may occur in late summer through fall.
For current advice on the use of several new products, see the new on-line spray guide. There are new products that appear quite promising, but they need to be carefully timed and applied to be fully effective.
Useful registered products include the ovicides such as Intrepid, Esteem and Rimon, the virus products, which are recently much improved, and nicotinyls such as Assail and Calypso.
Watch for Delegate (spinetoram) in spring of 2008, and Altacor (rynaxypyr) in late 2008, or 2009.
Azinphos-methyl – (Guthion, Azinphos-M). This product is being phased out by the EPA, and we will soon have to do without it. Azinphos is not holding up well in areas with higher numbers of moths flying. It does not work nearly as well as growers remember from the 60’s through the 80’s.
The product is applied by air-blast sprayer, 2 times per season (or a 3 lb./a active ingredient maximum for a growing year.) Number of necessary sprays depends on the number of codling moth present in the region near to the orchard, which is highly variable, and the CM numbers that may have developed within the orchard. If the problem is mostly due to external CM sources, some applications are made to the outside forty feet of the orchard, rather than the entire block. Rates applied range from about 1 to 1.5 lbs. AI/acre usually formulated as a 50% WP. (Two to three pounds of product per acre). This product was the standard control material for codling moth from the 1960’s, when it supplanted DDT and parathion. It was applied to the great majority of apple and pear orchards yearly.
Switching to the use of this product in the mid-1960’s allowed growers to eliminate the once-common use of miticides through integrated mite management. Other than the beneficial mite species, however, this product can be relatively or highly disruptive of various beneficial arthropods. . The product is considered effective for 17 days, less if heavy rains have washed protective residues from the foliage and fruit.
Pyrethroids – (Asana, Warrior, Brigade). The pyrethroids are cheap, effective, legal products with lower mammalian toxicity than other potential choices, but pyrethroids are highly disruptive of integrated mite management. Growers have wisely avoided the use of pyrethroid products as they would force growers to spray repeatedly to control the phytophagous mite complex, seriously disrupting apple orchard IPM. Historically, it has been simpler to manage codling moth than mites. These products are quite useful if the orchard is going to be removed soon, the moths are getting out of control, and you do not care about upsetting IPM on a site that is not going to be in orchard soon, or ever again.
Phosmet- (Imidan). Phosmet has been available for use for many years, but has gained very little acceptance, as it is perceived as less effective than the other control materials. It has some use as a “softer” material for growers trying to avoid the use of azinphos-methyl.
Horticultural mineral oil- Recent research has indicated that a 1% emulsion of highly refined, narrow range boiling point horticultural mineral oil applied at a per acre carrier rate that fully covers the tree may be effective as a codling moth suppressant. This spray is applied at 200, 400, and 600 codling moth degree days after the first significant flight of males are captured in pheromone traps.
Pheromone confusion: This approach has proven to be the most effective alternative control program in large trials and grower adoption over the past 16 years. Over half of the acres of Washington apples were treated with pheromone emitters during the past ten growing seasons. Growers apply pheromone releasing devices each season just prior to the flight of the first males. The pheromone in the orchard air make it very difficult for males to find and mate with females. Females that mate outside of the treated block may enter a pheromone treated block, or males may find and mate with females near the edge of treated areas where pheromone coverage is less consistent. Due to this “edge effect,” most successful pheromone treatments have been over very large acreages. Isolated or large treatment areas have had a history of successful control, with codling moth populations dropping to historic lows within the treated area. Control is not at all perfect, however, and chemical sprays are often used to supplement control throughout the treated area the first season, then to control outbreaks whenever necessary from the second treatment season and on. As the peromone treatment materials are initially more expensive than more traditional control methods, growers are reluctant to initiate this program during the recent difficult economic situation. In orchards with historically difficult to control codling moth populations, or those orchards irrigated by over-tree sprinklers, the combination of pheromone confusion and supplemental sprays have been more effective and economical than the alternatives.
Sterile moth release: British Columbia fruit growers have supported a very large program of sterile codling moth release (see photo) for the past several seasons. This has proven to be very expensive (about $200 per acre per year), and not as successful as early pilot projects had indicated. A great amount of Canadian Government, non-orchard landowner and grower support has been required to initiate and carry out the program. A cooperative project of sterile moth release in a large pheromone confusion project immediately South of the USA-Canada border has proven quite successful, though impractical on a wider scale.
Cultural Control Practices
The proper design of orchards and pruning of trees greatly improves spray application efficiency. Growers are advised to stack orchard props or fruit bins contaminated with over-wintering codling moth larva well away from orchards, if possible.
Few biocontrol agents for this pest presently exist in Washington. Trichogramma minutum, a small wasp that lays its eggs inside the codling moth egg, is often sold as a biocontrol agent, but is effective only in reducing the percentage of damage in very highly infested orchards. Efforts continue to identify effective predators and parasites in regions of the earth where apples are native, and transplant them into apple production regions. USDA ARS is especially active in this effort since the break-up of the Soviet Union improved access into the countries where Codling Moth and apple are native.
There continues to be quite an issue with “abandoned” or pulled orchards, and their impact on codling moth pressure in their vicinity. A few key points to ponder:
- Unsprayed orchards can lead to unmanageable numbers of codling moth in a vicinity. Unsprayed orchards continue to occur, but are not common. Every season a few more look as if they are not being cared for, often while they are in the process of being (eventually) removed. If there is an “abandoned” orchard in your vicinity, the local pest boards would appreciate being told about it. They will investigate, but may not find that it is the problem you suspect. If the orchard is going to be pulled sometime soon, there are cheaper, legal, and very effective codling moth control products that we don’t use in commercial blocks due to their effect on mite management. These may be used safely and effectively in an “abandoned” orchard. If cost is the factor preventing your late season control in a soon-to-be-pulled orchard, talk to your supplier about these possible low-cost options. These products are not recommended in commercial, viable orchards.
- Pulled orchards: Codling moth MUST have fruit to complete their life cycle. There are periods when the larvae and pupae live outside of the fruit, on or near the tree. Any larvae that successfully completed the first generation in May and June can emerge as adults during July and August of the current season. The larvae that emerge from the fruit during August, September and October may fly from the orchard during September of the current season, or in May and June of the next year. If an infested orchard has been removed, you can expect codling moth to emerge and fly from that area in May and June of the next season, even if the trees were burned or chipped, as some larvae over-winter off of the tree. Burning or chipping before bloom time of the next year greatly reduces the number of moths flying from the infested orchard, as most (80%?) of the codling moth overwinter on the tree, and will be destroyed during the tree clean-up. So burning or chipping is critical to the reduction of pest pressure in the region around the pulled orchard. “Working” the soil and prepping the site for planting the next Spring may kill most of the larvae that were over-wintering on the orchard surface.
However, one way or the other, codling moth will fly from the old, previously infested block, but only during the first generation (May & June) of the next season. They cannot complete their life cycle on dead trees, so will not fly from that site again until fruit is available from root sprouts.
Dead trees provide host material for shot-hole borer and ambrosia beetle, but other important pests such as leafrollers and scale die with the tree.
- Orchards being minimally managed may have any number of codling moths, from almost none to more than acceptable. An orchard may look bad, but have fewer codling moth than yours, or it may be a mess. If you are a neighbor, you may be able to guess the success of the codling moth management in that block, based on your trap counts.
- Orchards with current codling moth management: For many years, the industry standard for codling moth infestation was almost zero. Any signs of “worm” damage was a disgrace, and might have lead to dismissal of your fieldsman, complaints about the poor pest management skills of your neighbors, and intensified spray programs. As the one control product we used was very, very effective, keeping infestations under control was simple: spray. Adults, and larvae that had not yet penetrated to the core were killed, and residues effectively controlled the pest for about three weeks. Each time you sprayed, the codling moth had to start from “zero” in the orchard. Timing and coverage was much less important than it is today. Codling moth were few, and a missed spray did not lead to problems, as some of the spray applications were not necessary anyway. Not so today. Timing, rate and product choice does matter now. The increased numbers of codling moth in the region are due to a number of factors, some economic, some biological. This pest can be controlled, and it continues to be, but prevention of infestation is still the key, as “cleaning up” an orchard is much more difficult than it was ten years ago.