Obliquebanded Leafroller - A Persistent Pest of Apples

Most apple growers agree that obliquebanded leafroller (OBLR) has been one of the top five pests of apples over the past few years. So what is it about OBLR, that makes it such a challenge to manage in apple orchards? Unfortunately there is no easy answer to this question, but there are several different issues that likely effect OBLR management strategies.

Biology and monitoring

Unlike many other lepidopteran pests of apple (codling moth, oriental fruit moth), OBLR larvae emerge in the spring and begin feeding on the foliage of trees. Growers who are unaware of the biology of this pest may not be monitoring for the larvae, so early season damage may go unnoticed. Orchards with a history of OBLR damage should be monitored carefully in the spring, and insecticide sprays should be applied if populations are above threshold (12-15 larvae in 100 terminals inspected). The summer generation of OBLR can be very difficult to monitor due to the small size of the young larvae. This could lead some growers to believe that this pest is not a problem in their orchard, when there may be many tiny larvae present. In order to prevent unexpected OBLR outbreaks, the crop should be monitored closely for 1 to 2 weeks once 240 degree days Celsius (DDC) has been reached.

Timing of insecticide application

There is a relatively narrow window for targeting OBLR using insecticides, so the timing of insecticide applications is critical in managing this pest. Although insecticides against the overwintering generation of OBLR can be applied as early as pink, growers will get the most "bang for their buck" by waiting until petal fall. Often the emergence of overwintering larvae in the spring occurs over an extended period of time, so delaying sprays until petal fall will likely increase the number of insects that have emerged and are at the stage of development where they are susceptible to insecticides. For the summer generation initiating sprays at 240 DDC (when larvae are present in the orchard), optimizes the efficacy of the pesticide and may reduce the need for repeat applications.

Product choice

Proper choice of products is essential in managing OBLR effectively. In most commercial apple orchards, OBLR populations are resistant to organophosphates (Imidan®, Guthion®). More recently, researchers have shown that insect growth regulators such as Confirm®, and Intrepid® may not be as effective against organophosphate (OP) resistant OBLR populations. (Brunner, 2005). Growers have several options for managing OBLR, however, regardless of the product used, growers should always keep several important points in mind:

1. Good coverage is essential for good control, so keep sprayers calibrated and prune to keep the canopy open.
2. Understand the strengths and weakness of the products you are using. Many of the newer chemistries need to be consumed by insects, and although the insects may have ceased feeding they may not appear to be dead for up to 1 week.
3. Researchers have shown that the use of some products (Confirm, Intrepid) early in the season can cause sterility in insects from subsequent generations. The use of Bt early in the season has been shown to delay the development of OBLR, potentially affecting degree day models (Knight and Cockfield, 1997).
4. Use resistance management strategies, such as using the same chemical within a generation and rotating chemistries between generations. It wasn't long ago that apple growers had no products that were effective in managing OBLR, so let's be careful not to misuse the tools that we have now.
5. In Ontario, Dr. Pree (AAFC) has shown that resistance to OP in OBLR populations is unstable and that the use of reduced risk programs can result in reversion to susceptibility to OP insecticides.

Brunner, J., M. Doerr, J. Dunley. 2005. Insecticide resistance in obliquebanded leafroller, 1997-2004. Proc. 79^st Annual Western Orchard Pest and Disease Management Conference. Jan 5-7, Hilton Hotel, Portland, OR. Published by Washington State Univ., Pullman, Washington, pp 12.

Knight, A., S. Cockfield. 1997. Bts change the leafroller time clock in apple. Proc. 71^st Annual Western Orchard Pest and Disease Management Conference. Jan 8-10, Imperial Hotel, Portland, OR. Published by Washington State Univ., Pullman, Washington, pp 93-94.