Tree Fruit Research & Extension

New Insecticides for Apple and Pear IPM

Assail (acetamiprid) – Assail is the first neonicotinyl registered on apples and pears that has a high degree of lepidopteran activity, although it is primarily limited to codling moth. A short worker reentry interval (12 hrs), relatively short preharvest interval (7 days) and relatively low toxicity rating (Category III) allow more flexibility with Assail than the organophosphate insecticides that it will replace. Practical resistance management would suggest that growers should limit the number of neonicotinyl applications in a season, so care must be taken when adding Assail to a program that is already using Provado or Actara.

Lepidopteran pests
Codling moth – Initial tests with Assail indicated this product was very active against codling moth. In fact, Assail performed more like Imidan (and to some extent Guthion) than any new insecticide we have researched in many years. Assail can be applied at the same timing as Guthion and Imidan, with 2 applications per generation starting at egg hatch providing control of codling moth larvae similar to the industry standards. New evidence shows that when Assail is applied topically it is also highly toxic to codling moth eggs. A good resistance management strategy would be to limit Assail applications to one generation/year.

Leafrollers – We have not tested Assail in the field against leafrollers. However, laboratory bioassays indicate that Assail has only low toxicity to neonate larvae.

Lacanobia fruitworm – We have not tested Assail in the field against Lacanobia. However, laboratory bioassays indicate that Assail has only low toxicity to neonate larvae.

Indirect/secondary pests
Assail has good activity against leafhopper and the green aphid complex, with lesser activity against rosy apple aphid and woolly apple aphid. Assail also is a good campylomma material (and possibly thrips) and since it only has a bee toxicity rating of III it can be used at bloom when bees are not active. Leafminers are on the label but we do not have any experience with Assail against this pest; we would expect suppression like other neonicotinyls.

Pear pests
Assail has much the same activity as Actara and Provado for pear psylla and grape mealybug. It is relatively safe for bees, and can be used before bloom at the optimal timing for controlling both pear psylla and grape mealybug. The relative efficacy of Assail against pear psylla is reduced with late summer applications, so Actara may be a better option at that time. Assail is similar to Actara and Provado with regards to the same positive effects of adding oil as an adjuvant, and the same negative effects on campylomma.

Assail appears to have potential to become a viable alternative to Guthion for codling moth control in pear. However, because of resistance management concerns, it should be viewed primarily as a control for pear psylla and grape mealybug. With the current alternatives available for codling moth control (mating disruption, insect growth regulators), neonicotinyls such as Assail should be used carefully against codling moth as they would be selecting for resistance in pear psylla.

Beneficial arthropods
Given the efficacy against codling moth, the tendency may be to use multiple applications in a season, however both a 2- and 4-spray program have caused detectable mite flareups, some quite severe. At least some of this effect is attributable to a deleterious effect on predatory mites. This effect has been quite consistent in orchards with previous history of mite problems, thus risk of mite disruption is rated high in such areas. However, risk is mitigated if only a single application is made to an orchard with a stable mite situation. The addition of 1% oil to an Assail spray (the oil itself is miticidal) may help to reduce mite flare-ups in some, but not all, situations. The cumulative effect of multiple neonicotinyl applications for multiple years is unknown, but elevated risk is probable.

Tree Fruit Research & Extension Center, 1100 N. Western Ave, Wenatchee, WA, 509-663-8181, Contact Us