May 1, 2002

Vol. 4 No. 4

New Insecticides for Codling Moth Control

Codling moth control in the Northwest has relied upon organophosphate insecticide sprays for decades. Guthion (azinphosmethyl) and, to a far lesser extent, Imidan (phosmet) have been central parts of most apple and pear growers pest management programs and have provided cost-effective control.

Recently the Environmental Protection Agency (EPA) made the decision to allow uses of these products with some additional use restrictions for 4 more years. What will happen in 4 years, or even this year once the EPA completes its review on cumulative organophosphate risks (August 3, 2002), is any one's guess. The likelihood is that both materials will no longer be available for apple and pear growers or restrictions will be even more severe than at present. Restrictions on use rates and reentry intervals (particularly for Guthion) have already made their use a problem for many growers.

Several new insecticides have been registered in recent years for codling moth control. The most effective new materials are Esteem, Intrepid and Assail. Extensive research trials have been done with these materials and growers and consultants are now gaining field experience with them. These new insecticides are less harmful to many types of natural enemies and may allow for increased biological control of a number of orchard pests. They are also of low toxicity to orchard workers. Summarized below is some key information on these insecticides.

Esteem (pyriproxyfen) - This insect growth regulator functions as a juvenile hormone mimic. It is a highly selective insecticide, providing suppression of codling moth without disrupting activities of many biological control agents. Esteem has low toxicity to mammals and has a short worker reentry interval (REI) of 12 hours, but a long pre-harvest period (PHI) of 45 days. Esteem is limited to two applications per season and a total of 10 oz. of the 35WP formulated material per acre per season.

Esteem has activity against the codling moth egg, acting as an ovicide when eggs are deposited on the Esteem residue. The first application for the first codling moth generation should be applied soon after moths start flying (75-100 degree-days after biofix). In most situations a second application of Esteem should be made 14 to 21 days following the first. This approach provides active Esteem residues during most of the egg-laying period of codling moth. Esteem is best used against the first codling moth generation when the egg laying period is compressed; this timing enhances its efficacy and pre-harvest intervals are not an issue. As eggs don't move (!), thorough coverage is essential to achieve maximum effect with this material.

Esteem is not considered to be a strong codling moth control tool and should be used in a pest management program that includes mating disruption. It can be a very useful tool in this kind of program because applications made to kill codling moth eggs will coincidentally provide control of leafrollers.

Intrepid (methoxyfenozide) - Intrepid causes a premature lethal molt in many species of lepidopteran larvae. The larvae are unable to complete the molt and die within the old skin that cannot be shed. In some cases, Intrepid will not kill the larva but the subsequent adult will be sterile. Intrepid has little or no contact activity and must be eaten by larvae to have a toxic effect; therefore, thorough spray coverage is essential. This product should be used with a spreader or a low concentration of horticultural mineral oil to enhance coverage. Intrepid does have a strong ovicidal effect on codling moth eggs that are deposited on spray residues. Intrepid has the advantage over some older insecticides in having a short REI (4 hours) and PHI (14 days).

Intrepid as a codling moth control has primarily been targeted against young larvae before they can enter the apple. The Environmental Protection Agency (EPA) considers Intrepid an organophosphate replacement (OP replacement). However, this product is not a simple replacement for Guthion. It does not provide the same degree of crop protection as Guthion or Imidan under the same use pattern. To achieve control of codling moth approaching that provided by Guthion or Imidan requires one additional application of Intrepid in each generation.

In a 2001 test at the WSU-TFREC more damage was found when Intrepid use was started at the more t raditional "hatch" timing (250 degree-days) than when it was started at the "oviposition" (75-100 degree-days) timing. In this test two additional applications of Intrepid were made at 14-day intervals following the first spray. These data confirm laboratory studies showing a strong ovicidal activity of Intrepid. If further research confirms that the oviposition timing of Intrepid is as good or better than the egg hatch timing it opens a new strategy for using this product. Because Intrepid also has good activity against leafrollers its use at petal fall (approximately 75-100 degree-days) could simultaneously control codling moth and leafroller. Intrepid should not be considered a "stand alone" control for codling moth except with very low populations. It has its best fit as part of a pheromone-based IPM program where it is integrated with the use of codling moth mating disruption. There is some concern, based on experiences in California, Canada and France, that Intrepid use might encounter codling moth populations that are difficult to control due to cross-resistance with organophosphates.

Assail (acetimiprid) - Assail is in a relatively new class of insecticides (chloronicotinyls or neonicotinoids) that are synthetic analogs of nicotine. Assail, and other chloronicotinyls like Provado and Actara, act at the nerve synapse like nicotine acetylcholine. In tree fruits they are generally systemic insecticides and have their highest activity when ingested. Unlike Provado and Actara, Assail has good activity on codling moth. Assail does have contact insecticidal properties but the residue is relatively short-lived on the plant surface. Assail, like Esteem and Intrepid, is relatively safe for mammals, and requires a low level of personal protective equipment for applicators.

Assail received a registration for use on apples and pears in March of 2002, so there has been very little large-scale field experience with this product to date. In replicated small-block tests in 2000 and 2001 where Assail was applied with an air-blast sprayer it performed well against codling moth. Applied at the same timing interval as Guthion or Imidan, two applications per generation starting at egg hatch (250 degree-days), Assail provided codling moth control similar to these well-known standards. In a small plot test where treatments were applied by a handgun sprayer, Assail was statistically as good as Imidan or Guthion in preventing fruit injury. All of the tests at the WSU-TFREC were conducted under very high pest pressure and the minor differences in efficacy observed between Assail and Guthion or Imidan would probably not be evident in commercial orchards In a large plot test applied by an orchard air-blast sprayer Assail did not perform quite as well as Imidan. where codling moth pressures are much lower.

One problem noted with Assail use is a consistent increase of spider mite populations. Both 2- and 4-spray programs have caused spider mite flare-ups in tests, some quite severe. This observed effect is probably the result of Assail's toxicity to predatory mites, whose populations were reduced in these tests. In addition to the possible negative impact on predatory mites, Assail might also stimulate spider mite reproduction. Most Washington apple orchards have good integrated mite control, requiring no post-bloom miticide applications. Assail use should be limited to one or at most two applications to reduce the chance of disrupting integrated mite control. A good strategy for using Assail this year would be to replace an OP insecticide, for example at a second cover timing, that would allow farm workers to re-enter the orchard within a day to continue activities such as fruit thinning.

Other non-OP Codling Moth Insecticides
The above three insecticides are the most effective of the registered organophosphate replacements, although Intrepid and Esteem are not equal to Guthion or Imidan in efficacy. Other materials are registered for codling moth control that are even less effective, but may have a place in a multi-tactic pest management approach. Some brief comments:

1. Horticultural mineral oil: Oils are used mostly by organic growers who have few other insecticide options. Oil acts as an ovicide, killing eggs by limiting oxygen availability. Frequent applications, at 7-14 day intervals, may be needed throughout the egg lay period to achieve best control. Oils are best used in conjunction with mating disruption. There is concern with possible acute and chronic phytotoxicity associated with oil use.
2. Surround: This is a kaolin clay product that has been tested against codling moth and has provided suppression, with three applications per generation, similar to mineral oil (60-70% reduction in damage). As a comparison registered OP insecticides with two applications per generation regularly provide 90-99% reduction in damage. Post-bloom use of Surround can disrupt biocontrol of several pests, including spider mites and leafminer.
3. Avaunt (indoxacarb): This recently registered material has shown good activity against lacanobia fruitworm and pandemis leafroller, but is relatively weak on codling moth. In several trials from 1999-2001 it provided only 60-70% reduction of damage, despite as many as five applications per generation.
4. Success (spinosad): This material has been used for four years as an effective leafroller control. Codling moth is on the Success label and it does have activity if applied often enough; however, it is best reserved for control of leafrollers to limit opportunities for resistance development. The active ingredient (spinosyn) is a naturally derived fermentation product from an Actinomycete fungus. If a reformulation is approved for organic use it could provide a more effective alternative for codling moth control for those growers.

• spray coverage is more critical than ever
• more sprays will be needed for equivalent control, e.g. three Intrepids where two Guthions are adequate
• these materials are best suited for use with mating disruption

Contact Us

Ted Alway, Coordinator Areawide II
Phone: 509-663-8181 x268
E-mail: alway@wsu.edu

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