Management of the Obliquebanded Leafroller and Organophosphate Insecticide Resistance with Soft Pesticides in New York Apple Orchards 2000
Project Leaders: H. Reissig, A. Agnello, J. Nyrop, and R. Straub, Department of Entomology, NYSAES, Geneva, NY 14456
The 2000 growing season marks the completion of the second year of a proposed three-year research project with the following objectives: (1) To determine if populations and fruit damage from OBLR will decline in commercial orchards treated with soft pesticides for several consecutive seasons because of the effects of natural enemies (parasitoids and predators). (2) To determine if resistance levels of OBLR to organophosphates and other classes of conventional pesticides will decline during 2-3 growing seasons in plots set up in commercial apple orchards treated entirely with soft pesticides. Plots, ranging in size from 4-30A, were set up initially in 1999 in 5 commercial orchards in Wayne and Orleans Co., and in a research orchard at Geneva. A growerís standard plot of similar apple cultivars and tree training systems, which was treated with a normal, organophosphate based insecticide program was used as a comparison for the ìsoftî insecticide plots on each farm. Colonies were collected from 4 of the 5 commercial orchards during early spring prior to the beginning of the first and second season of the project and laboratory bioassays were conducted to compare the susceptibility of each population to two organophosphates commonly used in NY orchards, Guthion and Lorsban. Treatments of soft pesticides were continued in the research plots during the second year of the program (2000) throughout the season.
The results of monitoring the susceptibility of ovewintering OBLR during the start of the 200 grwoing season in the blocks that had been treated with soft pesticides the previous year showed that organophosphate resistance is fairly stable in populations of OBLR in NY apple orchards. Therefore, multiple seasons of reduced selection pressure may be necessary before resistance levels substantially decline.
The total amount of OBLR damage was considerably lower in all of the soft pesticide blocks than in the standard comparison plots during the 2000 growing season The average total damage at the end of the season was less than 2.0% in most of the soft insecticide blocks. The overall percentages of clean fruit in the soft blocks were similar at harvest to those in the comparison blocks. However, plum curculio damage was observed in several of soft blocks, particularly near the borders next to woods. The general levels of curculio damage in these soft programs was higher at the end of the 2000 season than in the initial year of the trial. No damage from internal lepidoptera or apple maggot was observed in either the standard or soft plots. Populations of foliar pests such as mites, aphids, leafhoppers, and spotted tentiform leafminers were low throughout the season in the soft blocks.
Although the results on the second year of this study appear very promising , this work should be continued at least one more season to determine if the reductions in OBLR populations and damage and acceptable levels of fruit damage from other major pests in the soft blocks can be sustained for multiple seasons. Also, it will be essential to continue to monitor the susceptibility of the populations of OBLR in these blocks to determine the stability of resistance to organophosphate resistance under this soft pesticide regime. Ultimately, this study may have to be expanded to include substantial numbers of representative orchards in areas throughout NY state that have chronically experienced severe damage from OBLR.
If continued studies show that OBLR populations can be reduced to low, sustainable levels under this type of selective pesticide regime, it is likely that NY growers in areas that are severely infested with this pest will implement this program within a very short period of time. Unfortunately, insecticide costs for this type of selective management program may be somewhat higher than a standard schedule relying on conventional broad spectrum materials. However, long-term studies in orchards treated with conventional control programs, have shown that OBLR populations persist at damaging levels from year to year in chronically infested areas in spite of the continued heavy use of insecticides specifically for control of this pest. In contrast, the adoption and implementation of this type of program could result in a long-term solution to the management of OBLR and the rest of the orchard arthropod pest complex. Ultimately, in the future if FQPA regulations result in the elimination of organophosphate insecticides from use in apple orchards, growers may have to adopt this type of selective insecticide program on their entire apple acreage throughout NY state.