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FINAL REPORT FOR 1999-2000

TITLE: Management of Leafrollers in Apple

PRINCIPAL Alan L. Knight, Yakima Agricultural Research Laboratory, ARS

INVESTIGATORS:

CO-INVESTIGATORS: Steve Cockfield, Scientific Methods

FUNDING HISTORY: Funding in 1995-1996 (Year Initiated): $ 22,998

Funding in 1996-1997 (2nd Year): $ 29,000

Funding in 1997-1998 (3rd Year): $ 29,500

Funding in 1998-1999 (4th Year): $ 46,000

Funding in 1999-2000 (5th Year): $ 31,000

Total Project Funding: $158,498

SIGNIFICANT FINDINGS:

Sublethal exposure to Bt endotoxins causes severe retardation in larval development. Inclusion of

this delay into a predictive phenology model improved the prediction of pupation and adult

emergence.

Sex pheromones can be used effectively in combination with the use of insecticides to manage OBLR

populations. Current sprayable formulations are short-lived. The Isomate CM/LR dispenser is

effective but runs out of pheromone before the end of the season. New dispensers being developed

are effective.

Aerosol puffers when placed internally in the orchard at 1 per hectare and integrated with border

treatments of hand-applied dispensers are effective.

A three year area-wide program effectively managed both codling moth and obliquebanded leafrollers

using the Isomate CM/LR dispenser plus reduced use of insecticides.

OBJECTIVES:

Evaluate the effects of Bt endotoxin ingestion on leafroller larval development and develop and then

validate a predictive phenology model for leafroller emergence and egg hatch following spring Bt

spray applications.

Evaluate the effectiveness of various hand-applied sex pheromone dispensers, sprayables, and puffers

for mating disruption of leafrollers.

Evaluate the adoption of a sex pheromone-based area-wide management program for both codling

moth and the obliquebanded leafroller.

PROCEDURES:

Field studies were typically conducted in replicated 20-40 acre orchards in the Brewster region.

Orchards were treated with various mating disruption systems including hand-applied dispensers,

sprayables, and aerosol devices. Orchards were monitored with traps and both larval sampling and

fruit inspections. Emission rates of the various hand-applied dispensers were monitored throughout

the season.

Laboratory studies with either Bt or sex pheromone components were conducted with the Yakima

OBLR strain under controlled temperature and light conditions.

RESULTS AND DISCUSSION:

The first year of the project focused on both the use of Bacillus thuringiensis sprays and both handapplied

dispensers ( Hamaki-con and Isomate CM/LR dispensers) and sprayables to manage

leafrollers. Various field and laboratory studies were conducted that evaluated the influence of larval

ingestion of Bt endotoxins on subsequent rate of development and pupal weight. A predictive

phenology model for leafrollers was developed which included the delay in larval development

following sublethal ingestion of Bt endotoxins. We also surveyed eight endotoxins and reported that

the most active toxins are the ones currently being used in the Bt products available to growers. Other

studies demonstrated the importance of temperature on the effectiveness of Bt sprays and led to the

development of a set of recommendations on how growers can optimize their use of these products.

Studies with the pheromone dispensers and sprayable formulations were conducted in 10 – 40 acre

replicated blocks and the results were encouraging. Moth catches were reduced > 90% and orchards

treated with leafroller pheromone had similar levels of fruit injury as untreated blocks but were

treated with $80 per acre less insecticide. The CM/LR dispenser performed well but was found to run

out of pheromone late in the season. The sprayable formulation was found to work best at a rate of

24 g per acre and lasted only three weeks.

Studies conducted during the second year of the project again focused on the Bt-phenology model

and the use of sex pheromones to disrupt leafrollers. The Bt-model was validated for OBLR and was

found to significantly improve the prediction of pupation and adult emergence in orchards treated

with Bt sprays in the spring. The CM/LR dispenser was evaluated in three 20 acre orchards and fruit

injury was reduced 64% compared with orchards treated with similar numbers of insecticide sprays

but without leafroller pheromone. Also during 1997 six 40 acre orchards were split and treated either

with 200 or 400 Isomate CM/LR dispensers per acre for codling moth and obliquebanded leafroller.

Moth catches and fruit injury did not differ between treatments. The evaluation of the sprayable

formulation in 20 acre orchards demonstrated that multiple applications of this formulation were not

effective in managing seasonal leafroller populations.

From 1998 to 2000 a 450 areawide project was conducted with 12 growers who treated their orchards

with the Isomate CM/LR dispenser for disruption of both codling moth and obliquebanded leafrollers

(OBLR) for three years. Orchards were treated with 200 dispensers per acre and supplemental sprays

of Bacillus thuringiensis or spinosid were applied for leafrollers. Results were compared with 150

orchards in the Brewster Areawide Management program treated with Isomate-C+ plus insecticides

only for leafrollers. Moth catches of codling moth and obliquebanded leafroller were reduced > 95%

during the study. Fruit injury for both codling moth and leafroller were reduced > 60% and the

number of insecticide sprays for codling moth and leafrollers was decreased by nearly two sprays per

season.

Aerosol puffers were evaluated in four 40 acre orchards for OBLR in 1998, three orchards in 1999

and nine orchards were treated with dual canister in 2000. In all cases orchards were treated with 16

puffers placed one per hectare and the perimeter of the orchards were treated with the hand-applied

dispensers for leafrollers and/or codling moth. Moth catches and fruit injury varied widely among

blocks yet mean moth catches and percent fruit injury did not differ from surrounding orchards

treated with Isomate products during all three years. Also during 1999 we evaluated several

operational settings of the aerosol puffers to determine how best to release the pheromone. The use

of 15 minute intervals for sprays releasing 7.5 mg of pheromone for 12 hours each day (3 pm to 3 am)

was found to work the best.

Laboratory studies showed that the levels of E11-14:AC present as a contaminant with the pheromone

component, Z11-14:AC does not significantly reduce disruption of mating for Pandemis pyrusana at

levels from 0.25 – 6.0% in the formulation.

CONCLUSIONS:

Effective use of Bt insecticides is dependent upon minimizing sublethal larval exposures. Factors

such as, the formulation’s array of endotoxins, field temperature, larval age, spray rate, and time to

resumption of larval feeding should be considered in optimizing the use of Bt insecticides.

The use of various methods to disperse leafroller sex pheromone can be an effective tool to manage

populations especially when integrated with a reduced- use of insecticides.

REFERENCES:

Knight, A. L. 1997. Optimizing the use of Bts for leafroller control. Good Fruit Grower 48: 47-49.

Long, L. E., M. Omeg, A. L. Knight. 1997. Monitoring obliquebanded leafroller in sweet cherry

orchards. Oregon State University Extension Service, Wasco County.

Knight, A. L., L. A. Lacey, B. Stockoff, and R. Warner. 1998. Activity of CryI endotoxins of

Bacillus thuringiensis for four tree fruit leafroller pest species (Lepidoptera: Tortricidae). J. Agric.

Entomol. 15: 93-103.

Knight, A. L., D. R. Thomson, and S. D. Cockfield. 1998. Developing mating disruption of

obliquebanded leafroller (Lepidoptera: Tortricidae) in Washington State. Environ. Entomol. 27:

1080-1088.

Knight, A. L. and J. E. Turner. 1998. Sexual biology of Pandemis pyrusana (Lepidoptera:

Tortricidae) under laboratory conditions. J. Brit. Col. Soc. Entomol. 95:89-94.

Knight, A. L. and J. E. Turner. 1999. Mating disruption of Pandemis spp. (Lepidoptera:

Tortricidae). Environ. Entomol. 28: 81-87.

Lacey, L. A., A. L. Knight, and J. Huber. 2000. Microbial control of lepidopteran pests of apple

orchards. pp. 557-576 In Field manual of techniques in invertebrate pathology: Application and

evaluation of pathogens for control of insects and other invertebrate pests (L. A. Lacey and H. K.

Kaya, Eds.) Kluwer Academic Publishers, Dordrecht

Abstracts for 10 posters presented at the annual Washington Horticultural Association meeting are

published in their Proceedings.

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