Washington State University Cooperative Extension

Areawide IPM Update

The Newsletter of Pheromone-based Orchard Pest Management

Vol. 2, No. 7 -- June 1, 1997

Cooperating agencies: Washington State University, Oregon State University, University of California, U.S. Department of Agriculture, and Chelan County.

Cooperative Extension programs and employment are available to all without discrimination.

Leafroller models: predicting development and timing controls

Leafrollers are an increasing problem for many orchardists in the Northwest. Two species are responsible for almost all of the damage found: the pandemis leafroller (PLR), and the obliquebanded leafroller (OBLR). Monitoring trees for larvae is difficult and time-consuming, and pheromone traps have been unreliable indicators of the need for leafroller treatments. Proper timing of sprays is known to be crucial to successful control programs, particularly with Bacillus thuringiensis (Bt) materials that are only effective against larvae.

Research on OBLR phenology has been conducted over the past three years by Jay Brunner and Lyla Lampson in the Milton-Freewater, Oregon, area, and a predictive degree-day (D) model has been developed. Further modifications to the model will be made in 1997, particularly with regard to predicting moth flight. The model predicts flight and egg hatch for both generations of OBLR. Predicting the hatch of summer generation eggs could be most useful for improving the timing of monitoring and control programs. A similar model exists for pandemis leafroller (PLR), details of which can be found in the book Orchard Pest Management, published by the Goodfruit Grower. Although similar to the OBLR model, it differs in small but important respects, having a lower temperature threshold for development.

This model predicts the beginning of OBLR flight approximately 1000-1100 D after March 1, generally mid- to late May in Milton-Freewater. This gives an indication when pheromone traps should be in place. The first moth catch in a pheromone trap, or biofix, is the starting point of the model. Degree-days are calculated daily from this point and at approximately 400 D from biofix, eggs of the first generation will begin to hatch. Egg hatch period lasts about 400 D, or until about 800 D after biofix. Predicting egg hatch allows consultants to better focus their efforts in monitoring for summer larvae, which when young are very difficult to find, and aids in the timing of sprays aimed at their control.

The use of Bt products against the overwintering larvae around bloom time can often have sublethal effects, causing delayed development of some larvae, but not death (see Areawide IPM Update, April 1, 1997). This effect makes the model less accurate in predicting summer generation egg hatch, as hatch is delayed or becomes more protracted. Several consultants who use the leafroller model have accounted for this delayed development in their programs by not setting biofix with the first moth caught, but delaying it until the first surge in catch, perhaps 10 or more in a week. This surge can be one or more weeks after the first catch. Alan Knight, of the USDA Yakima lab, is working on a leafroller model that will account for the sublethal Bt effect.

A lookup table is available which provides accumulated OBLR D in 10 unit increments and percent of OBLR moth flight and egg hatch as predicted by the model. You may obtain a copy of this table online or from Ted Alway in the WSU Cooperative Extension office in Wenatchee.

Timing Sprays for Summer OBLR Control

Camp site updates - late May, 1997

The use of mating disruption for codling moth control has continued to increase in the Western United States. In 1996 almost 34,000 acres were estimated to have been treated with pheromone dispensers, of which almost 20,000 acres were in Washington. Information from the three dispenser manufacturers indicates that an estimated 45,000 acres were treated in the West in 1997, with close to 26,000 acres in Washington. Estimating acreage under MD is complicated by the increasing use of the Isomate dispensers at less than the full rate. The Codling Moth Areawide Management Program (http://pwa.ars.usda.gov/yarl/areawide/areawide.html) has grown substantially this year, with the addition of five new sites, increasing the total acreage from close to 3200 acres in 1996 to nearly 9500 acres in 1997.

Randall Island - The RIP is now in its fifth year of mating disruption for codling moth. Isomate-C+ is used by all growers at 400 dispensers/acre, and was applied by the first week of April, close to 10 days after biofix. The use of a delayed "hang time" is intended to extend the useful life of the dispensers in this hot and high CM pressure area, and avoid a second dispenser application. Close to 70% of the project received a cover spray, generally aimed at the second peak of the first generation flight. (In California, two distinct peaks are seen in the first generation flight, often called the "A" and "B" peaks.) About 25% of the acreage, most of which has not been treated for almost 3.5 years, will receive two applications this year to suppress slowly increasing CM and leafroller populations.

Ukiah - Full bloom in this Mendocino County site occurred about March 22, with a good crop of pears on the trees at this time. CM flight began soon after bloom, and catch in traps has been running well below that of last year. In 1996, through the "A" peak, an average of 1.8 moths/trap/week was found. This year the number is down to 0.4. Isomate-C+ was applied by all growers in late March at 400/acre, with plans for a second application of 200/acre to be applied at approximately 1000 D, around the second week of June. Only 50 acres of this 550 acre project received a cover spray, based upon a higher trap catch (4 moths/trap/week) and a history of higher pressure.

Carpenter Hill - Full bloom in the Medford area began in late March with Anjous, extending into mid-April with apples. At this point, the crop appears to be average in size, with good quality. CM biofix was established on April 15 at this site. Isomate-C+ dispensers were applied at 400 per acre to all blocks by mid-April. This site uses foliar horticultural oil applications for supplementary control of codling moth, psylla and mites. The first application of oil was completed by May 12 (200 D), with a second one planned for 400 D after biofix. CM catch so far is equal to or less than last year.

West Parker Heights - Full bloom on apples occurred at this site around April 20-22 and, like most Washington orchards, was generally lighter than last year on apples, particularly Red Delicious, and good on pears. CM biofix was set for April 25. Isomate at 400/acre has been applied to 470 of the 480 acres of this site, with the remainder in Checkmate CM. Isomate Special, a dispenser containing both codling moth and leafroller pheromone, is being used on 40 acres. Warm weather following bloom has accelerated CM flight, and at least half of the CAMP site will receive a first cover. No other pests are of general concern at this point.

West Wapato - This first year CAMP site in the Yakima Valley totals 964 acres, including 100 acres of non-bearing fruit, and involves 19 growers. Full bloom on apples occurred about April 24-26, and CM biofix was set for April 26. Isomate-C+ has been applied to 781 acres, with Checkmate CM being hung on 83 acres. Close to half of the Isomate acreage here is using this product at half rate. All growers plan to supplement mating disruption this year with one or more cover sprays targeting the first CM generation, depending upon history and trap catch.

Howard Flat - Total acreage treated at this site has reached 1650 acres, with the addition of 550 acres in the Chelan River area. Biofix was set for May 5 for Chelan River, and May 8 for Howard Flat. Participation on Howard Flat is now 100%, with the inclusion of the orchard that was not involved the past two years. CM catch on the Flat has been quite low despite the high temperatures, with only 126 moths in 455 traps through May 22; 90 of these came from just six traps in the newly participating block! The Chelan River area has some blocks with high CM pressure, many of these near bin piles, backyards or "under-managed" trees. All growers are using Isomate-C+, with an increasing number using less than the full rate. Most growers in the Chelan River area will be applying at least one cover, but some on Howard Flat may elect to go with mating disruption only this year.

Manson - This new CAMP site along the north shore of Lake Chelan includes 1014 acres of monitored bearing orchard, involving 68 growers and 96 different blocks. Bloom was "mixed" but warm weather has permitted good pollination and set. All growers are using Isomate-C+. Most have applied the dispensers at 200 per acre; some are using up to 400 per acre. May 9 was established as CM biofix, and all growers are encouraged to apply a first cover. Close to 360 traps are being used for CM monitoring, and leafroller traps will be installed shortly. CM catch in traps has been high in areas with historically high CM pressure and in non-pheromone blocks within the treated area. There is also a large increase in MD use in the Chelan Valley this year outside of the CAMP sites.

Brewster - This new CAMP site, known as BAM, is by far the largest of the ten sites, with 2400 acres being monitored this year. Together with the extensive acreage in the area that has been using MD for several years, there are close to 4500 acres in the Brewster area treated with CM pheromone dispensers. BAM involves 60 growers, and 520 CM traps. Leafrollers in this area have historically been a pest equal to or worse than CM for many growers, and leafroller pheromone traps will be in place before expected flight. Most growers are using Isomate-C+ at 200 dispensers per acre, with an increased rate applied to some borders. CM biofix was set for May 7, 9 or 10, depending upon elevation. Moth catch is generally low, with the exception of some hot spots. Most growers are expected to apply a first cover spray for CM.

Progressive Flat - This fifth new CAMP site contains 582 acres, farmed by 24 growers. All participants have applied Isomate-C+, mostly at 200 dispensers/acre with a small acreage containing 300 or 400/acre. Biofix was set on May 12. Initial CM catch the first two weeks of monitoring has been low for most of this site, despite high temperatures. Close to 75% of the traps show no catch through the third week of May, but all growers have been encouraged to apply at least one cover in this first year of the project. Leafrollers have not been a problem here in the past, but pheromone traps for both pandemis and obliquebanded leafrollers will be installed by June 1, and growers are aware that leafrollers have increased at other sites with the reduction in cover sprays.

Lake Osoyoos - This site has doubled in size this year to close to 800 acres, with additional acres on both sides of Lake Osoyoos. A total of 24 growers are now involved. All growers are using Isomate pheromone dispensers, mostly at 400/acre, but some are opting to install lower rates of 200 or 300 per acre. With the exception of two blocks, all dispensers were installed by full bloom (May 7). CM biofix was set on May 9. Initial CM catch in the original acreage, now going into its third year of MD, has been very low, almost nonexistent, and growers are not planning on any cover sprays. The release of sterile moths from the SIR facility in Osoyoos, British Columbia, began on this acreage and on close to 80 acres of the expansion on May 8. Included this year is a 28- acre block in the middle of the original site that did not participate in CAMP the first two years, and experienced very high CM populations for multiple reasons. Moth catch in the expansion acres has ranged from none to high: all expansion growers are planning to apply one or two covers for the first generation.

Ted Alway, Editor
Phone: (509) 664-5540
Fax: (509) 664-5561
e-mail: alway@coopext.cahe.wsu.edu

Partial Funding provided by: Washington State Tree Fruit Research Commission, U.S. Department of Agriculture-Agricultural Research Service.

WSU Cooperative Extension, Chelan County
400 Washington St.
Wenatchee, WA 98801

Wenatchee WA, 28 May 1997