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Oriental fruit moth: next generation or tail end of the first one?

In addition to its influence on insect growth and development, temperature can have a profound effect on insect activity. Just as there is a base temperature below which no development occurs in immature forms, there is also a minimum temperature required for activities including adult flight and searching for a mate. When it's too cold, adult OFM are not active in the orchard. They are not looking for mates; they are not laying eggs. But they are still out there. When temperatures rise, mated females get back to laying eggs. In addition, some of the overwintering generation that didn't quite make it to adulthood prior to things cooling down will continue their development and emerge to mate and lay eggs.

The result can be what is being reported in some tree fruit production areas (Niagara, SW Ontario) this spring: Things were really warm, OFM flight was on the upswing and an apparent peak had, in some cases, been reached. Then all of a sudden, things got cold over the May long weekend - really cold - and activity ceased. With several days of hot weather followed by more seasonal temperatures, activity resumed and adults are once again being caught in pheromone traps. Many people have wondered if the "new" activity marks the beginning of the second generation of OFM. The answer is no; there haven't been enough heat units (degree days) accumulated for this to have occurred. The adults that are being caught now represent the tail end of the overwintering generation.

All of this can lead to challenges in management, and in some cases, additional insecticide sprays by the grower. If numbers being caught in traps haven't tapered off yet and the last spray was a couple of weeks ago, a second spray may be required to protect shoots and / or developing fruitlets. All growers should be aware of the residual activity for the pesticides they are using. For the management of OFM in apples, the recommended reapplication interval is 10-14 days for Intrepid. Assail should be reapplied after 12 days. Check labels for intervals recommended for pyrethroids, as they vary considerably depending on the active ingredient. Keep in mind that at this time of year, the trees will outgrow the residues quickly. If the pesticide has worn off, and traps are still catching a significant number of OFM (for arguments sake, let's say more than a third to a half as many as during the first peak), then a second application of insecticide should be applied. For resistance management, make sure that the 2nd insecticide application is the same product that was used for the first spray-don't rotate chemistries within a generation (rotate between generations instead).

Be aware that a split or bimodal peak in the overwintering generation usually translates to the same thing occurring in the second flight. For this reason, in areas where a bimodal peak (also called a "peak and shoulder") has been observed, growers using insecticides to manage OFM should be prepared to apply two sprays to manage the second generation, as indicated by activity in pheromone traps during the next flight period. Growers who are using mating disruption for the management of OFM in apples and / or tender fruit have the luxury of not having to worry about this.