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FINAL REPORT FOR 1999-2000

TITLE: Leafroller Biology and Potential for Control with Insect Growth

Regulators

PRINCIPAL David R. Horton, Yakima Agricultural Research Laboratory, ARS

INVESTIGATORS:

CO-INVESTIGATORS: Alan L. Knight, Yakima Agricultural Research Laboratory, ARS

FUNDING HISTORY: Funding in 1999-2000 (Year Initiated): $21,014

SIGNIFICANT FINDINGS:

Newly hatched larvae of oblique-banded leafroller were more susceptible to field-weathered residues

of CONFIRM than late instar larvae.

Mortality of small larvae occurred on CONFIRM residues field-aged for up to 5 weeks; large larvae

were killed by field-residues of 3 weeks in age.

Egg hatch was reduced on 1-week old CONFIRM residues early in the season but not later in the

season; spray coverage may have been better early in the season.

OBJECTIVES:

Determine whether moths collected from CONFIRM-treated orchards show reduced fecundity and

egg fertility (as suggested by earlier laboratory trials by Knight and Horton).

Quantitatively describe field-persistence of CONFIRM against oblique-banded leafroller larvae and

egg-masses.

PROCEDURES:

Light traps equipped with mesh bags were placed in CONFIRM-treated and untreated orchards to

collect live female moths. As with last year, captured moths were entirely male, thus the project was

discontinued.

CONFIRM was applied with a standard airblast sprayer to a 10 acre block of ‘Gala’ apples on May 1,

2000 and again on June 6, 2000. The application rate was 17 oz of product per 100 gallons of water

per acre. Foliage was collected from this orchard and a neighboring unsprayed orchard 24 hours

following application, 1 week following application, and 3 weeks following application. Foliage

samples were placed in large glass vials to which a single OBLR larva per vial was added. Two

larval ages were compared: newly hatched larvae and 4th – 5th instar instar larvae. There were 25

replicates per treatment combination. Survival of larvae was determined at 4 days and 7 days.

We allowed laboratory-reared moths (OBLR) to deposit eggs on field-collected foliage. Egg masses

were collected and allowed to hatch; number of larvae hatching was determined for each egg mass.

After hatch had been completed, area of the egg mass was determined using a LI-COR area-meter.

Hatch is expressed as number of larvae per cm2 of egg mass. Sample sizes were 5 to 20 egg masses

per treatment combination (adults were highly variable in egg-laying capacities, which explains the

variable sample sizes).

The experiment was repeated in early August at the experimental orchard located at Moxee. Two

rows of Golden Delicious apples were sprayed with CONFIRM using a small airblast sprayer pulled

by an ATV. Two control rows were sprayed with water. Foliage was collected at 24 hours, 1 week, 3

weeks, and 5 weeks, and assays were conducted as above. Rates were the same as at the commercial

site.

RESULTS AND DISCUSSION:

Light-traps equipped with mesh bags collected only 10 moths; all were male, and the project to

determine effects of field residues on field-collected, female moths was discontinued.

Figure 1 shows larval survival at 4 days (panels 1 and 2) and 7 days (panels 3 and 4) for small and

large larvae fed foliage collected in early May. The grower applied Guthion between the week 1 and

week 3 foliage collections, so the survival data for week 3 reflect the combined effects of Guthion

and CONFIRM residues. Mortality of small larvae on the 1-week residues was 100%; mortality

approached 100% for the large larvae.

Figure 2 shows larval survival for the June experiment. Again, the grower applied Guthion before the

week 3 foliage sample could be taken. Mortality of larvae fed 1-week old residues was again high,

irrespective of larval age.

Figure 3 shows results for the Moxee orchard, and indicate that small larvae suffered high mortality

rates up to 5 weeks following the CONFIRM application (panel 3), and that large larvae suffered high

mortality rates up to 3 weeks following the spray (panel 4).

Figure 4 shows that egg hatch rates were severely reduced on CONFIRM-treated foliage for the two

trials conducted in the commercial orchard. However, there was no significant reduction in egg-hatch

for the trial conducted in August at the experimental orchard in Moxee (Figure 5). Our results for the

larval survival suggests that we had better spray coverage at the commercial sites than at the Moxee

site (compare Figures 1-2 vs Figure 3), which may explain the poor egg-kill for the Moxee

experiment.

CONCLUSIONS:

CONFIRM residues provided kill of newly-hatched and large larvae of oblique-banded leafroller up

to and exceeding 3 weeks following the application. Results for egg-kill were less clear, due to poor

results for the August trials; however, results at the commercial orchard for applications made in May

and June suggest that residues caused substantial egg mortality at least up to one week following the

spray application.

Figure 1.

Survival of

small and large

larvae after 4

days or 7 days

feeding on fieldcollected

foliage. Early

May study.

Commercial

orchard.

Guthion

application

made between

weeks 1 and 3.

Figure 2. Survival of small and large larvae after 4 days or 7 days feeding on fieldcollected

foliage. Early June study. Commercial orchard. Guthion application made

between weeks 1 and 3.

Figure 3. Survival of

small and large larvae

after 4 days or 7 days

feeding on fieldcollected

foliage. Early August

study. Moxee

(experimental)

orchard.

Figure 4. Larvae hatched per square cm of egg mass. Commercial orchard.

Figure 5. Larvae hatched per square cm of egg mass. Moxee experimental orchard.

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