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Delayed Dormant Sprays for Leafrollers

Monday Jan 02, 2023

Pandemis leafroller (PLR) and oblique-banded leafroller (OBLR) have different phenologies which are well documented on DAS. Delayed dormant sprays can work well for PLR, but are generally too early in the season for efficacy against larvae of OBLR.

Traditional leafroller (LR) control programs begin with a Lorsban application at the delayed dormant (or half-inch green) stage of bud development. In recent years there has been a shift in LR species in most commercial orchards from PLR to OBLR. Both LR species over-winter as small larvae in hibernacula in bark crevices or other protected areas on the tree. While the majority of PLR larvae have emerged from their hibernacula by the delayed dormant stage, OBLR do not complete their emergence until approximately three weeks later.

As a result, the effective Lorsban residues decline prior to the full emergence of the OBLR population limiting the value of the delayed dormant treatment. Predictive models for both PLR and OBLR are available via DAS that will help growers improve timing for OP-alternative insecticides as well as improve decisions about when to sample for LR larvae to get a better estimate of population densities or efficacy of previous insecticide applications. Optimizing LR timing with OP-alternatives will make it possible to move away from a reliance on delayed dormant Lorsban for LR control.

(Jay Brunner, Keith Granger, and Mike Doerr, WSU-TFREC)

Traditional LR Programs