Washington State University Cooperative Extension

Areawide IPM Update

The Newsletter of Pheromone-based Orchard Pest Management

Vol. 2, No. 2 -- February 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.

Horticultural spray oil effects on pear tree productivity and fruit quality

There is increasing use of foliar oils, particularly on pears, for the benefits they can provide in controlling mites, pear psylla, codling moth and other pests. Their use is limited mostly out of concern with possible fruit or tree damage, both in-season or over time. Rick Hilton, with Oregon State University in Medford, is conducting studies with Orchex 796 oil. The oil is applied with a handgun as a 1% spray to pears three times per season, at 200°D, 400°D and 600°D after biofix. Effects are being studied on Bartlett, Bosc and Comice in Medford, and Bartlett and Anjou in Hood River.

After one year, the effects on fruit size and fruit set show no significant difference between the oil treatment and the control (no oil). Differences in yield are also insignificant, although there is a trend for all cultivars to have yield reduction with the oil treatment. With fruit weight, however, it appears that both Medford Bartletts and Hood River Anjous have lost about one box size. No difference has been found with the other cultivars. In fact, Bosc fruit may even be a bit larger. With regard to fruit finish, increased russet was observed with the oil treatment on Bartletts, but in neither location was it enough to downgrade any fruit. Overall, Bosc seems to be a more oil tolerant cultivar, and Anjous the most susceptible.

Fruit bins as a source of codling moth

Bins have long been recognized as a source of codling moth when they are placed in piles in or near the orchard. The concern with this source has increased in recent years. This is due to the perception that bins have become more heavily infested with increasing CM populations, and from the increase of orchard pest control programs with greatly reduced use of organophosphate insecticides, such as those using mating disruption. In these programs a chemical insecticide barrier doesn't exist to protect against a source of moths that bin piles can contain.

Brad Higbee, of the USDA-ARS Entomology Lab in Parker, WA, began studies in 1996 to investigate how bin piles influence CM populations in nearby orchards, and whether CM can be forced to emerge early by covering piles with plastic. Bin piles were constructed and diapaused CM pupae were placed within them at several levels. The piles were then covered with clear plastic sheeting.

Covering with plastic did warm the piles considerably and forced moths out some three to four weeks earlier than in uncovered piles. In the uncovered piles, in which CM pupae were placed in late March, the peak moth emergence was in early June, with the last ones out in early July. Further studies are planned in 1997.

Biological control of leafrollers with Colpoclypeus florus

Leafrollers are parasitized by many wasps and flies, which can provide fairly effective leafroller control in many native habitats. Because leafrollers are primarily foliar feeders, not preferentially attacking fruit, there is hope that by encouraging parasitism in orchards we can gain substantial control benefits. Colpoclypeus florus is a eulophid wasp originally from Europe that was found in Washington in 1992. It is one of the most effective parasites in finding and parasitizing leafroller larvae.

Techniques have been developed by Jay Brunner and Bob Pfannensteil of the WSU-TFREC for rearing this parasite in the lab to permit releases in orchards, in an attempt to establish new populations there. The rearing has proven to be laborious and expensive, but 52,000 female C. florus were released in 1996 at 14 sites with leafrollers in northern Oregon and Washington. They attempted to release at sites having both substantial leafroller populations and minimal insecticide use, an uncommon combination. Even Bt sprays, which are not toxic to the parasite, affect the extent of parasitism by either killing the leafroller larvae or by the sublethal effects of Bt of delaying and changing leafroller development.

There was mixed success in establishing C. florus populations in many of the release blocks in 1996. Because rearing this parasite is so expensive, precluding the use of regular, annual releases in orchards, the research emphasis is shifting towards how to encourage the successful overwintering and development of C. florus populations. There are several successfully established populations in the Wenatchee and Orondo areas that overwinter well and have provided 50-60% parasitism of leafrollers in the spring and 70-80% in the summer. This success may rest upon there being a suitable overwintering host for the parasite. C. florus passes the winter as a larvae associated with a nearly mature leafroller larvae. The orchard leafroller pests in Washington overwinter either as small larvae or eggs, so a suitable leafroller host will need to be found on other plants, either native or cultivated, nearby or in the orchard. Several leafrollers were found in 1996 in Central Washington on alfalfa and weeds that may prove to be good hosts for this parasite.

Codling Moth Monitoring and Control: Survey Results

Codling moth (CM) is the key pest for most apple orchards in the Western US. Orchard pest control programs often revolve around the cover sprays targeted for its control. Deciding if a control treatment is needed, and what that treatment will be, is one of the most important pest control decision made each year. How, then, is this important decision made?

To answer this question, I surveyed 25 pest control consultants in the summer of 1996. Ten were private pest management consultants, nine represented agrichemical distributors, and six were from fruit packing warehouses. Nine work primarily in the Yakima Valley, five work mostly in the Columbia Basin, and eleven work in North Central Washington. All but two consultants had at least five years experience with pest management in Washington apple orchards, with several having consulted for more than 20 years.

Pheromone Trap Use
All consultants used pheromone traps to monitor codling moth to some extent. Trap density ranged from one trap per 5 to 40 acres, depending on CM pressure, block size, knowledge of CM history for the block and more. Most common with the private consultants was a density of one trap per 5 to 7 acres. Many said they would trap at a higher density, but didn't have the time to check more traps. Most put the traps in the orchard by bloom; some delayed this until near the end of the first CM generation, using traps only to help with second generation control decisions.

Almost all used a wing-type trap, such as the Pherocon’ 1CP, baited with a red rubber septa containing 1 mg of codlemone. Traps were generally placed at 5'to 7' in the tree canopy. The frequency of replacing lures varied considerably. Most changed them at 3 or 4 week intervals, with several making the change at one month or more. (Investigations in Yakima and Wenatchee have shown that to maintain consistent attraction the red rubber lure needs to be changed at a 3 week interval in the spring, and every 2 weeks in the summer. Longer lasting lures have been investigated and are available.)

In blocks using CM mating disruption, most consultants increased trap density (to one trap per 2.5 to 7 acres), used a 10 mg septa as a lure, and hung the traps higher in the orchard, averaging 8' to 10'. To access these higher traps, most stood on the seat of a 4-wheeler, or attached an extension of bamboo or PVC to the trap wire to lift the trap up to a high limb and bring it down for inspection.

Codling Moth Model
Twenty-two of 25 consultants used the codling moth model, as adapted by Brunner and Hoyt for Washington orchards. Most said it was the key to proper timing of cover sprays. Many said it helped them interpret trap catch and determine the need for a third cover for the first CM generation. Many relied upon reports based on the model, put out by Cooperative Extension or an agrichemical distributor, to track CM development and determine spray timing. Biofix, the first consistent moth catch in pheromone traps, was determined by close to half of the consultants using their own traps, while others used information from Cooperative Extension, the full bloom date on Red Delicious, or even the first date after bloom when the temperature at dusk is 60°F or higher.

Treatment Decisions
These consultants used many different approaches in deciding whether CM control was needed. Thirteen of the 25 interviewed used trap catch throughout the season as the principal means of deciding whether to treat for codling moth. Ten recommended treatment for the first generation regardless of trap catch, using trap catch only for second generation decisions. Two considered trap catch only indirectly in their control decisions.

The action threshold, or catch that indicates a treatment need, varied greatly among consultants, just as the trap density did. Many applied first cover regardless of catch, and used a threshold for later treatments. Many also reduced the threshold in the second generation, when traps are less efficient. Two consultants with over five years of experience of using action thresholds with CM, and monitoring over 3000 acres between them, use one trap every 5 to 6 acres. Their thresholds are similar, recommending treatment with a cumulative catch of ca. 5 moths/trap in the first generation and 3 to 4 moths in the second. Both have never had a significant problem with this approach but have seen a general increase in CM populations and the development of isolated but nagging hot spots. They questioned whether this was due to using too high an action threshold, CM resistance to Guthion, or a combination of the two. Their response has been to lower the threshold for the first cover to 2 to 3 moths accumulated/trap, or to consider a blanket cover regardless of trap catch every 2 to 3 years.

Insecticides Used
Guthion 50W (azinphosmethyl) remains the material of choice of all this group of consultants. Few use less than 2#/acre any more, with nine advisors recommending up to 2.5# or even 3# in higher pressure situations. Three commented that they exceeded 2# in recommendations for the first time in 1996.

Penncap-M was used by some, mostly where there was a leafroller concern as well. Several stated that they had improved CM control with its use. Many used it as a last resort, having observed or fearing that its use will disrupt biological control, particularly of aphids or leafminers.

Lorsban was little used by this group for CM control. Imidan was also rarely recommended. One consultant was enthusiastic about the use of horticultural oils for CM control, applying up to 6 or 7 applications of 1% oil timed for egg hatch.

Codling Moth Pressure
Seventeen of the consultants have observed a definite increase in pressure over the past 5-10 years, and five saw no clear trend. A NCW consultant noted that average trap catch has nearly tripled over six seasons, with the number of covers almost doubling in that period. Two consultants in Yakima commented that trap catch has become almost continuous in many blocks, with there no longer being a distinct gap between flights. Most consultants suspected that this increased CM pressure was due to azinphosmethyl resistance.

In general, the response has been to:

  1. increase insecticide rates - most now recommend azinphosmethyl @ 2# or more.
  2. increase the number of applications - many comment that they now recommend two more covers now than they did 5 to 8 years earlier.
  3. decrease the spray interval - with azinphosmethyl, the most common insecticide used, most recommend an interval of 17-20 days, shortening this to 14-17 days with high CM pressure or overhead irrigation.
  4. use more Penncap-M or Lorsban - some recommend more use of these insecticides, believing they provide better CM control and help with resistance management.
In summary, most consultants across Washington State are seeing increased CM pressure, and growers are responding with increased insecticide use, particularly of azinphosmethyl. Focusing CM control efforts on the first generation is emphasized by many consultants as the "key" to a successful control program. Many are concerned that orchardists are losing the ability to have economical and effective CM control. As a response to this concern, in part, there is increased interest in and use of mating disruption of CM. Seventeen of the consultants interviewed have experience with mating disruption and most are pleased with the results, particularly when supplemented with insecticide use. Many express a concern with the difficulty of monitoring CM in mating disruption blocks, and with the development of more time- and information-intensive pest management programs in general; "We need more consultant-friendly schemes", says one. In the Columbia Basin, where CM pressure is generally less than the other regions, leafrollers are often the greater concern. Consultants across the state also identify overhead irrigation and bin piles as frequently contributing to or aggravating CM problems.

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, 31 January 1997