Managing OFM in Apples with New Products

The tool box for managing oriental fruit moth (OFM) in apples continues to be filled with new products, offering growers more options for pest management. While these new insecticides are efficacious, their timing of application may differ from older conventional products targeting newly hatched larvae. Many reduced- risk products must contact the target insect life stage directly or be ingested. Good coverage, timing, and accurate monitoring are all essentials in managing pests in apple orchards today, and this certainly applies to a serious direct pest such as OFM.

In the past, recommendations for timing application of insecticides have been based on pheromone trap catch data, between 3 and 6 days following peak activity (6-10 days following rapid upswing in numbers) depending on the time of year. Several of the new products need to be applied much earlier - in some cases shortly after adults emerge and begin to lay eggs, or before eggs begin to hatch. For this reason, the use of degree day developmental models and egg hatch prediction models are now required to ensure appropriate timing.

Recall that there are 3 generations of OFM in Ontario. A partial fourth generation may develop in some years, with adult flight and egg-laying activity extended into October. The insect overwinters as a late stage (4th or 5th instar) larva within a cocoon under bark scales, crevices and other protected areas on the tree or on the ground. They pupate in the spring and emerge as adults in late April or early May. Pheromone traps are used to track their emergence and flight.

Fluctuating spring temperatures can affect trap catch data. Just as there is a base temperature below which no development occurs in larvae, there is also a minimum temperature required for activities including adult flight, searching for a mate and egg-laying. During cool nighttime periods often experienced early in the growing season, adult OFM may not be active in the orchard for periods of several days. When warmer temperatures resume, so does flight activity. This may give the impression that the flight of the second generation has begun, when in fact the activity represents a split or bimodal peak of the overwintering generation. Bimodal peaks often carry-over to the next generation.

Pheromone traps will provide information on insect activity, but in order to understand what is actually happening at a population level will also require the use of degree-day models to verify that enough heat units have been accumulated to drive the pest to the next generation. A phenology model to predict development of OFM from egg to adult (generation time) is available. Oriental fruit moth have a base developmental temperature of 7.2ºC and require an accumulation of approximately 550 DDC base 7.2ºC to go from an egg to an adult (generation time). If you are seeing a fresh flush of adults but have not yet accumulated enough heat units, then the new activity likely represents a bimodal peak rather than the beginning of the next generation.

A degree day-model to predict the percent egg-hatch for OFM is also available. Both models have been used with success in apple IPM programs in several production areas to help time insecticide sprays. Note that while degree day models can provide important information for predicting the timing of insecticide applications, they are not a replacement for continued monitoring of pest activity with pheromone traps and field scouting for damage.

When using the OFM model, begin accumulating degree days (base 7.2ºC) at the first sustained moth catch (biofix) of the overwintering generation in pheromone traps placed in apple orchards and continue to calculate these for the remainder of the season.

The timing of insecticide applications varies depending on the products being used. For products targeting newly hatched larvae such as Delegate, Calypso, Assail, Altacor*, timing is approximately 194-208 DDC for the first brood (generation), 805-833 DDC for the second brood, and for the third brood two applications at 1361-1389 and 1611-1667 DDC to cover extended activity (where required). Check residual activity of products and re-apply as required where extended flight occurs. For products that need to be applied before eggs are laid (residues under eggs) such as Rimon, application should occur at least 100 DDC earlier for each generation. For products that need to be applied prior to egg hatch (residues over eggs and /or timed for first hatch) such as Intrepid or Altacor*, application should occur 50-80 DDC earlier for each generation. Monitor flight for each generation, check residual activity for each product and re-apply product if necessary.

Keep in mind that larvae enter the fruit within 24 hours of hatching. Rapid entry into the fruit means that there is a very narrow window of opportunity for contact with insecticides on the surface, and many newer products must be ingested. Adequate spray rates and good coverage are essential for growers using insecticides to manage OFM.

When using insecticides, each generation should be managed as separate units. Use products from a single chemical group to manage a given generation of a pest. If emergence and/or activity for that generation is prolonged (for example, due to bimodal or split peaks), apply a second application of the same product. This exposes each generation to only one chemical group. Rotate to another chemical group for each subsequent generation.

Mating disruption of Oriental fruit moth is a highly effective alternative to insecticides. The technology is readily incorporated into IPM programs for apples, offering season-long protection against OFM damage (depending on product choice), and without the need to time insecticide spray applications. Dispensers must be applied prior to flight. Mating disruption is a key tool in preventing / delaying the development of resistance to insecticides.