Abstract:
The seasonal biology of the obliquebanded leafroller, Choristoneura rosaceana (Harris), was studied to improve its management in Mid-Columbia area sweet cherry orchards. Overwintering OBLR larvae began to emerge from hibernacula at bud stage 2 (side green). Most overwintering larvae emerged from hibernacula within three weeks of first bud swell and were randomly distributed in the canopy of cherry trees. Most of the overwintering generation pupated by the end of May. The overwintering generation flight began in late May with the first moth catch used as the Biofix for degree-day accumulation. Flight of the overwintering generation peaked (50% catch) at an average
of 104 ± 2.5 (SE) degree-days. First eggs of the overwintering generation were found at
85 ± 0.8 (SE) degree-days from Biofix. All summer generation eggs had closed by 572
± 10.1 (SE) degree-days. The first summer generation larvae large enough to be detected
in fruit bins (third instar and larger) were found at an average of 686 ± 12 (SE) degree days.
Rates of larval development on leaves of different hosts as well as artificial diet were recorded. This information was used to determine developmental thresholds. The estimated lower developmental threshold of OBLR larvae reared on foliage was
significantly greater than that for larvae reared on artificial diet. Analysis of phenological data determined that a lower threshold of 6°C and an upper threshold of 30°C yielded the lowest coefficient of variation.
Differences in development rate of OBLR larvae on young and old leaves from various tree fruit hosts were described. Development rate was significantly faster on young leaves than old leaves for cherry and pear. There was no significant difference in development on young and old apple leaves. Cherry leaf age had no effect on development when leaves were taken from non-growing shoots. Larvae on pear developed faster on young than old leaves from growing and non-growing shoots. Larva development was faster on leaves collected early in the season than on leaves collected later in the season.
The Washington OBLR phenology model was tested for OBLR in sweet cherry. This model provided accurately described the flight period of the overwintering generation as well as the chorology of summer generation egg hatch. However, the model did not accurately describe the flight of the summer generation.
Selective insecticides and timing strategies were evaluated for OBLR control. There was no improvement in control by applying delayed dormant sprays before or at peak emergence of overwintering larvae. Spinosad was as effective as chlorpyrifos when applied pre-bloom to control OBLR. Spinosad and methoxyfenozide effectively controlled summer generation larvae.
