Tips on managing Obliquebanded leafroller (OBLR) in Ontario apple orchards

Adult obliquebanded leafroller (OBLR) moths have started to emerge and fly in many areas and growers are making decisions on whether to manage this pest, and what products to use if necessary. OBLR has been a problem in many areas in Ontario, however there has been an increased incidence of leafroller damage in Norfolk orchards in the past few years. Damage from OBLR larvae is particularly troublesome in orchards late in the season. Pin point damage from these late feeding larvae to the fruit, can slow the picking crews down considerably during grading at harvest. It is too late to manage larvae once damage is present, so targeting the larvae that emerge from these adults is the last opportunity to avoid late season damage.

OMAFRA recommends petal fall sprays in orchards that have historical problems with OBLR, or have high populations in the spring. Before determining whether management may be necessary for the summer generation of OBLR, it is important to be aware of the extent of overwintering larvae which survived petal fall treatments. Monitoring for the presence of larvae and damage from the summer generation is important to determine if summer sprays are needed for this pest. More growers are applying petal fall sprays for leafrollers, and excellent products are available for managing this pest, so we are seeing fewer overwintering larvae surviving.

While trap catches and the use of developmental models provide useful information on timing insecticides for the summer generation, they do not provide an adequate indication of the abundance or potential damage from leafrollers in orchards. Trap catches vary depending on the placement of the traps in the orchard, and they can attract insects both from within the orchard and from neighbouring habitats. Thus trap counts do not provide an adequate evaluation of OBLR populations or the potential for damage in the orchard. Larval assessments should always be used to determine if management of summer generation OBLR is necessary.

It is important to predict when larvae should begin to appear in orchards, since they can be overlooked during monitoring. Traps are placed in the orchard at petal fall and models are triggered after first sustained moth catch occurs. 50% catch of the overwintering generation occurs at 77.8 DDC, base 6.1°C after biofix. 1% egg hatch begins at 244 DDC, base 6.1°C and 95% egg hatch occurs at 433 DDC base 6.1C). Immature larvae are very small and can be difficult to see. Small larvae are present at 500 DDC, and mostly large larvae are present at 666 DDC (Brunner et al., 1997). Larvae initially feed on tender growing terminals, water sprouts and developing fruit, however after the 3rd instar, larvae often cause more damage to fruit. Monitor for emerging larvae by examining 10 shoots on 10 trees for the presence of larvae or feeding damage. Also check 10 fruit from 10 trees for the presence of damage. Larvae are approximately 25 mm in length when full grown, and are green in colour with a brown or black head capsule. Often damage is more apparent in orchards than are larvae. Larvae roll leaves forming a shelter and use silk webbing to attach leaves to a fruit or to attach leaves together. Management is recommended if 1-2% of the terminals or fruit are infested. The orchard should be re-sampled again in the next 3-5 days to ensure that the population wasn't underestimated.

If sprays are necessary OMAFRA recommends applying an insecticide at 240-280 DDC (base 6.1° C) when larvae are active in the orchard. For those of you that are internet savey you are probably aware there are several different phenology models published on obliquebanded leafroller, and each model has a different minimum threshold (ranging from 6.0, 6.1,7.2, 10, or 10.8° C) and maximum threshold. The most recent published research from Washington suggests that the lower threshold is 10° C and the upper threshold is 30° C from egg to adult are 10° C to 30° C. This model suggests that at temperatures above 30° C developmental rates of leafroller larvae are reduced, and increased mortality of larvae occurs at 34 or 36° C. Traditionally we have not used an upper threshold for our model in Ontario. This upper threshold may explain why in some years (particularly hot years) our model predicts larval emergence earlier than when we see the larvae appearing in orchards. We are hoping to evaluate this newer model under field conditions in Ontario, but at present, we continue to use that developed by Brunner et al. (2007). Timing is very important when managing OBLR. Although we used to think that targeting the small larvae was critical in OBLR control, Dr. Pree (formerly of AAFC) found that the insecticides worked just as well against older larvae as they do against young larvae. It is most important that products are not applied too early. OBLR emergence can occur over an extended period of time and applying products too early can leave little residue to manage late emerging OBLR, and may cause growers to have to re-apply another insecticide.

OMAFRA received funding from the Ontario Fruit and Vegetable Convention last year to initiate a trial evaluating the thresholds developed in Washington under Ontario conditions. Preliminary results from last year indicated that the model we are currently using in Ontario was more accurate than this new model for our conditions, however we are continuing this study this year so stay tuned for more results.