Frequently Asked Questions About OFM in Apples

As most Ontario apple growers by now are aware, oriental fruit moth (OFM) is a major pest of apples in North America. This pest has come to the forefront in the past few years, but there is still a lot of confusion as to what the damage from this pest looks like, whether sprays should be applied to control it, and how sprays should be timed if needed. We will try to answer some of these questions, however, it is important to keep in mind that researchers and crop specialists are still learning about this insect and its biology in apples, so there are still a number of questions that remain unanswered for now.

How do I know if I have OFM damage in my orchard?

OFM damage is not as obvious to see in apple orchards as it is in peach orchards. However, once you know what the damage looks like, it is easy to monitor an orchard for damage. Growers who had high levels of internal lepidoptera damage (Figures 1 and 2) last year should have a qualified crop consultant monitor their orchard for OFM (using pheromone traps and by conducting damage assessments).

The 1^st and 2^nd generation OFM will tunnel into terminals (Figure 3), eventually causing the terminals to wilt. First generation larvae generally attack the terminals, however, in some cases they will also attack the fruit - as we have already seen this year.

Figure 3. OFM damage in apple terminal

Should I spray for OFM in my orchard?

Currently there is no economic threshold for OFM in apples in Ontario. Pheromone trap catches do not give an accurate indication of the amount of damage that will be incurred in the orchard. Pheromone trap catches should only be used to monitor the presence of the insect and to determine the timing of sprays. They should not be used to determine if control measures need to be applied.

If low numbers of OFM are being trapped in your orchard, and there is no prior history of OFM damage (or internal lepidoptera damage) then there is no need to start a management program for OFM. However, if you had internal lepidoptera damage last year, and OFM moths are active in your orchard, you should discuss OFM management options with your crop consultant. Timing of sprays to control OFM is critical in managing this pest. The larvae move into the fruit within 2 hours of hatching, at which point in time they are well protected from any insecticide application.

Are there any models available for predicting the development of OFM?

While models predicting the development of OFM and timing of spray applications have been developed and are being tested in Michigan and Pennsylvania, these models have not been validated in Ontario. As a result, they may not provide accurate timing of sprays. As with other insect models, it is important to remember that models should always be used in conjunction with field data (pheromone trap counts) to time spray applications. Models have been shown to be less accurate in seasons like this year, where we had such a long, cool, wet spring. Using the model alone to time insecticide sprays may result in inaccurate timing and potential crop loss. However, models can be very useful for verifying field observations and validating the timing of insecticide sprays.

If insecticide sprays are necessary, what products are available and when should I time my sprays?

Always discuss with a certified crop consultant whether insecticide sprays are necessary to manage OFM in your orchard, and, if so, which products might work best for you. In orchards where management programs for OFM are necessary, OMAFRA recommends applying an insecticide at 6 days following the upswing of OFM populations (based on pheromone trap counts), or 3 days following peak flight. In apple orchards where OFM sprays are necessary, OMAFRA recommends the use of Assail (acetamiprid) to manage 2^nd and 3^rd generation OFM. (Assail is not currently registered on peaches). The number of applications of insecticide for the 2^nd and 3^rd generation will depend upon the emergence of adults. If there is a prolonged emergence, a second application of product (10-14 days later) may be required to manage this pest. However, if OFM emerges within a short period of time, one insecticide application may provide adequate control. As a resistance management strategy, always use the same chemistry if multiple spray applications are required to manage the same generation. Assail should be used no more than four times per season. Never use the same insecticide to target more than two different generations of OFM each year. The recommended rates for managing OFM in apples are as follows:2 Assail 240 g product/ha, Decis 250 mL product/ha.

What do I need to keep in mind when using mating disruption to manage OFM?

If you are using mating disruption to manage OFM, your pheromones should already be out in the orchard. If you haven't placed mating disruption pheromones out in your orchard as of yet, I would not recommend using mating disruption for OFM this season. We have already started catching moths from the second generation, so some mated moths are likely already present in your orchard. Mating disruption is not effective if pheromone 'twist ties' are used after flight has occurred. Growers using Isomate M100 should keep in mind that this product only lasts for 75 to 85 days. Growers who applied the product in late May will need to make a second application of twist ties around the last week in July.

How do I monitor in my orchard for OFM damage?

Pheromone traps should be placed in each orchard to monitor OFM populations. Traps should be checked by a crop consultant twice per week on the same days each week. Pheromone lures should be replaced after each OFM generation or every 6 weeks. No moths should be caught in orchards using mating disruption. A few male OFM in traps on the edge of orchards is not unusual but more than 5 moths caught in any mating disruption area trap is cause for concern. Other moths besides OFM will occasionally be caught in pheromone traps, so you must be able to identify OFM accurately - another good reason for hiring experienced, knowledgeable crop consultants to monitor your orchards.

Damage assessments should be conducted approximately 7 to 10 days after peak flight catch (based on regional trap data). Monitor a minimum of 50 fruit and 50 terminals from 20 trees for OFM damage (paying special attention to varieties such as Gala, Jonagold, and Mutsu).