Washington State University
Vancouver Research and Extension Unit
Vancouver, WA 98665-9752
The orange tortrix, Argyrotaenia franciscana (Walsingham), continues to be a key harvest contaminant of machine harvested cane berries in southwestern Washington and Oregon. This leafroller species expresses two to three generations a year, does not diapause and overwinters in a range of larval stages. Their larval instars web and feed on dead foliage, primocane tissues and fruit buds. Orange tortrix become problematic because the larvae will wiggle and drop from their feeding sites on silken threads when disturbed. The current control strategy is a prebloom spray in early May and the traditional clean-up/preharvest spray with Capture/Brigade to control summer larvae feeding on terminal primocane foliage to form leafolled shelters.
Effective insecticides are registered for the two timing intervals which include the: organophosphate malathion, carbamate carbaryl, pyrethroids esfenvalerate and bifenthrin, microbial Bacillus thuringiensis, insect growth regulator tebufenozide and the recently registered bacterial fermentation metabolites spinosad/spinosyn. The current arsenal of insecticides for leafroller control in red raspberry is very good given the climate for cancellation of many older chemistry compounds by EPA. However, canefruit growers in southwestern Washington and the Willamette Valley are reporting dissatisfaction with their preharvest control programs. Discussions have centered on population resistance to bifenthrin or whether to control first generation moth populations or their preharvest larval progeny. These issues were investigated in an area-wide mode in the Woodland’s Bottom region with grower participation and concurrence.
In collaboration with Tom Peerbolt, we held breakfast meetings with red raspberry and black berry growers in the Woodland’s bottom beginning in late March. Acreage of red raspberry was about 353 while that for black berry and evergreen black berry was 96 for a total of about 450 acres. The hands-on participation by this set of growers clearly dispelled the commonly held notion that OT in the Woodland bottom had developed resistance to bifenthrin and that a biorationale such as Success would not possess the residual to effect their feeding and leaf-rolling behaviors.
Laboratory cultures of the orange tortrix were propagated from populations taken from the Tsugawa Farm and WSU R&E Vancouver in 2003. These colonies were used for our 2004 lab bioassays testing the residual activity of field rates of Capture (bifenthrin) and Success (spinosad) to adult moths. Of major interest was the concern by the industry for the possibility that orange tortrix had developed resistance to bifenthrin in the Woodland bottom area. The recent registration of Success will provide an ideal alternative to the broadspectrum pyrethroids.
Area wide orange tortrix program in Woodland, WA, 2004. Prebloom discussions centered on: the life history/phenology of the orange tortrix, use and implications of area wide pheromone traps to measure onset and duration of male flight activity, sprayer calibration and assessment of coverage with water sensitive paper and grower consensus to apply malathion for adult moth control prior to 5% bloom. Pheromone counts indicated a depression of adult moths up to 3-4 day posttreatment. This suggests partial elimination of progenitors of the next generation of orange tortrix larvae. The latter have been of special concern to local IQF producers during late June and July harvest. Perimeter pheromone traps placed around the bottom’s region indicated orange tortrix refugia, flight and overwintering is primarily an in-field phenomenon. However, orange tortrix larvae are listed from 82 plants in the Pacific Northwest. Many of these are common to the hedgerows and numerous verges and riparian habitats alongside the Lewis River.
Intense monitoring was initiated by mid-May to locate orange tortrix egg clusters and to mark and observe them for the onset of larval hatch and migration to primocane terminals. The tactical plan was to apply either Bt treatment(s) or an application of the biorationale insecticide Success about one month from harvest. Timing for early larval emergence is critical during this time when they seek feeding domiciles on elongating primocanes through harvest. A standard bifenthrin, ‘clean-up’ application was applied at FMC’s projected 3 days PHI. Traditionally this application remains very effective for eliminating all instars of orange tortrix through harvest, including root weevil species and multiple insect contaminants as well.
Based on peak adult male trap counts that occurred between 31 May and 3 June, the growers applied Success (spinosad) at 0.094 lb(AI)/acre to cover foliage for earlier emerged OT larvae, hatching larvae and as an adulticide. All of the pheromone monitored field showed significant adult orange tortrix decline through 7-9 June. Degree-day accumulations, with a lower threshold of 41°F from 1 January, was 1,483 for observing the first F1 larva in the field. This compared favorably to the 1,270-1,370 averages for OT egg hatch with the 1988 OSU model. Because of an unseasonably mild spring, red raspberry maturity was advanced by 10-14 days. This increase in degree days accumulations resulted in the decision to apply Capture/Brigade (bifenthrin) clean-up spray on 14-16 June at 0.1 lb(AI)/acre. This application further depressed adult flight activity to the end of the month as well as no reported downgrading of IQF submitted product for the Woodland bottom growers. IQF growers risk rejection of their entire crop when one or more orange tortrix larvae are found in the finished product.
Population responses to lab applications of Capture and Success, 2004. Capture (0.1 lb(AI)/acre) and Success (0.094 lb(AI)acre) were applied with a Solo backpack sprayer to drip on 5 ‘Meeker’ hills each on the Vancouver R&E on 20 February. Every 24 hours to 5 days posttreatment, individual trifoliate leaves were place in a small water-filled vial stoppered with a cotton plug. These were placed in 6 inch Petri dishes along with one adult orange tortrix moth. Each of 6 treatments was replicated 10 times over a 5 day interval. Data reported represents mortality after 3 days of exposure to the respective 5 posttreatment regimes for two orange tortrix populations and each exposed to two pesticides and the untreated check. However, our experimental design held individual moths for 5 days of exposure to each of the field aged intervals. The results from these tests showed no significant difference between both field populations to Capture and Success. However, mortality for the slower acting Success was different compared with Capture on 1 and 2 day old residues. Adult mortality to residues was comparable with Capture after 3-4 days posttreatment and when held for 5 days, mortality was nearly complete for both registered pesticides.