Rose habitats to enhance leafroller biological control in pome fruits

Rose habitats to enhance leafroller biological control in pome fruits

Summary

In 2005, we made 142 collections of OBLR leafrollers at 24 orchards adjacent to experimental rose gardens. C. florus accounted for 70% of spring and summer parasitism near gardens established 2 or more years; spring parasitism of OBLR by C. florus led to higher summer parasitism (Psummer = (3.4) Pspring+27; R2 = 0.6), which often exceeded 90%. Four new gardens were planted in 2005 and six older gardens were re-infested with Ancylis. Results have/will be presented at 3 grower and pest manager venues over the winter. A collaborator used protein markers to track C. florus movement at one garden.

Objectives/Performance Targets

• 1. Evaluate the impact of large gardens (ca. 75 to 200 m2) of Rosa woodsii and wild strawberry harboring the strawberry leafroller, Ancylis comptana (SLR), which supports C. florus overwintering and enhances parasitism of OBLR and PLR in adjacent orchards.

  2. Disseminate information on how to establish, maintain and benefit from these alternate habitats through traditional presentations, grower magazines, a web site and consultation.

  3. Develop greater understanding of the ecology of this system, particularly how far into orchards will parasitoids disperse from gardens and the stability of the beneficial community in gardens with rose alone versus strawberry alone and rose plus strawberry.

Accomplishments/Milestones

Accomplishments under objective 1.
Since the inception of this work in 2001, eighteen growers and the PI’s lab group have planted 35 gardens of multi-floral rose and strawberries (34 single gardens plus 50 small gardens around one 500-acre orchard) throughout the major pome fruit centers of the Pacific Northwest. The objective of having many gardens over a wide geographic range is to test that this habitat manipulation is robust to geographic variation in climate and other biotic and abiotic factors.

At each garden we have attempted to establish the Strawberry leafroller, Ancylis comptana, document the use of this host by the parasite Colpoclypeus florus and to determine the impact of the availability of this alternate and overwintering host on the parasitism of pest leafrollers in targeted orchards in spring and summer. We monitor parasitism by C. florus and other parasitoids in orchards next to gardens using sentinel leafroller larvae (4th instar OBLR; 25 larvae/ branch, 10-20 branches/site, 3 sites/orchard)) produced in the laboratory. Larvae are deployed at 3 specific times: in spring and summer when pest leafrollers are in susceptible larval stages and again in fall when parasitism of sentinel leafrollers indicate that C. florus and other parasites are active and seeking overwintering hosts.

The positions of the 35 gardens are shown in Figure 1 (not shown online). These include 4 gardens planted in 2005, under our first year of WSARE funding.
Parasitism results are depicted in 3 ways: first is the season-long pattern of parasitism across all sites; second is the proportion of parasitism due to C. florus across all sites and all dates through mid August represented as a plot of C. florus versus total parasitism; third is the pattern of parasitism seen at 9 sites where parasitism was monitored in spring, summer, and fall. Figure 2 (not shown online) plots season-long parasitism showing that parasitism increases significantly throughought the season and that C. florus dominates the parasitism through most of the year, with two parasitic flies (Tachinidae) accounting for most of the remaining parasitism. Figure 3 (not shown online) plots spring and summer parasitsm by C. florus against total parasitsm. It shows that overall C. florus is responsible for 70% of all parasitism despite a significant number of sites/dates where almost all parasitism is due to tachinid flies.

Parasitism of our experimentally deployed sentinel hosts remained very high in late summer into fall (after mid-late August), when suitable stages of pest leafrollers are not found in or near orchards. This parasitism of fall deployed sentinels is coincident with C. florus parasitism of Ancylis leafrollers in the gardens. The overwintering hosts and biology of the tachinid flies remains unknown but their abundance after mid-August also suggests they may be subject to manipulation if a suitable overwintering host and habitat were found. Figure 4 (not shown online) provides some detail on seasonal pattern of parasitism at 9 sites where we were able to measure parasitism at spring, summer and fall periods.

In several gardens Ancylis failed to establish or were extirpated by pesticide drift or unknown cause (even possibly intensive predation). Six such gardens were reinfested with Ancylis in 2005. Still to be analyzed are samples from 25 rose gardens taken in late November-December designed to provide estimates of Ancylis abundance and parasitism by C. florus that help us generate expectations for parasitism in the orchards in the coming spring . These samples will be analyzed through February and results, predictions, and tests of predictions will be reported next year.

Accomplishments under Objective 2.

To date we have presented our results of the first year of this WSARE project at the third National Organic Tree Fruit Symposium held in Chelan WA in June and at the Washington Horticultural Association Convention held in Wenatchee in early December, in both cases as a posters. In the next 2 months results of the work in 2005 will be presented to the Washington Tree Fruit Research Commission both written and oral reports provided as both a professional debt after their funding of this work for the three years preceeding WSARE, and as a means to continue to reach new growers. Similarly this same 3 report types will be presented at the 79th annual Western Orchard Pest Management and Disease Workshop in Portland in January 2006. This targets other scientist and many pest control advisors.

We have created web pages describing how to implement gardens, from how and where to plant and maintain the roses, where to find infested roses for transferring Ancylis to your own garden, and with overviews of our results for the last 5 seasons. The website is not yet connected but will be in the coming months. Completion of this website represents an important milestone to be met before the end of 2006.

Milestone: Many in the grower community are familiar with this concept of using rose gardens to enhance leafroller parasitism based on the above presentations and ones made during 2001 to 2004 at various venues. A significant milestone in our work is the independent contacts initiated by growers who wish to consult us on how to establish gardens and our subsequent help in getting the strawberry leafroller established in the gardens they plant. Such was the path taken for the 4 new gardens planted in 2005. We will continue to provide such onsite visits and phone consultations throughout the duration of this project, and we are convinced the website will further grower confidence in striking out on their own to create these gardens in the future.

This is a long-term ecological experiment, and our work is far from completed. We have several deficiencies under objective 2 that need to be met, but the most important is identifying the cost of these manipulations to growers. We know the materials and supplies (black irrigation hose, couplers, ¾ “ PVC for risers, 5 sprinkler heads, 20-50 Rosa woodsii seedlings, weed cloth, bulldozing a clean area to plant, connection to the orchard irrigation) can be less that $200 for a sizable garden, but we need to formalize these estimates and make them available to the grower community.

Accomplishments under objective 3.

A greater understanding of the ecology of Ancylis and the various parasitoids in the rose gardens is our highest priority area of study. We have approached this by taking biweekly samples of rose and strawberry leaves in 6 gardens throughout the growing season, collecting the Ancylis larvae and pupae found in these, and recording the percentage of parasitsm observed. The collected Ancylis were preserved in alcohol, and headcapsule measurements are being made now to estimate instar distributions. By early spring a developmental model will be fit to these life stage estimates. The same data will be collected again in 2006. Ultimately we will have a day-degree driven model for Ancylis in the roses, and C. florus in both roses and orchard habitats.

During our biweekly samples in gardens we also sought evidence for predation of Ancylis. To date we have observed activity only by a Vespula species, mostly in July and August. Unfortunaely, predation combined with potentially high parasitism of Ancylis in August can lead to fewer Ancylis to provide overwintering hosts in fall. (We know from previous work that C. florus overwintering diapause is triggered by low temperatures experienced by larvae, and these conditions do not occur until mid-September at the earliest in Central Washington.)

Finally, we have collaborated with Dr. Vince Jones (Washington State University, Tree Fruit Research and Extension Center, Wenatchee WA) in developing a method to mark C. florus at gardens and capture them in orchards in order to determine the best placement and number of gardens in orchard landscapes. The preliminary work has resulted in a method to mark the wasp as it naturally emerged from the rose gardens and to capture it on host-baited traps. To date, the largest distance from a garden we have captured C. florus (in an orchard) with mark acquired in the rose garden is 128 m.

Impacts and Contributions/Outcomes

This report covers the first year of a three-year project. We have no impacts to report as this is too short of a time frame to measure the impact of such fundamental and broad-scale habitat manipulations. However, significant milestones are being met to aquaint the larger pome fruit grower community of the Pacific Northwest about the potential of rose garden habitats to enhance biological control of leafrollers. Potential impacts include dramatically reduced pesticide use for leafroller control in apple pear and cherry and a more biocontrol-oriented selection and timing of control methods used for the codling moth and aphids in the crops.

Collaborators: