April thru September, 1997
WSU Nooksack Watershed IPM Project with several grower collaborators/mentors:
Funded by Environmental Protection Agency, Clean Water Act, Section 319 grant; administered by Washington state Department of Ecology.
This mentoring project exposed growers to regular and systematic scouting for key insect, mite, and disease pests in raspberries during the 1997 growing season. Growers periodically reviewed portions of a draft IPM scouting manual which forms the basis for scouting efforts and decision making. This manual is formatted based on crop stage and pest development. Scouting efforts and results reported here are a component of a specific task as identified in this grant. Cooperating growers have and will continue to communicate this scouting experience to other growers in various forums.
Three fields were scouted on an as-needed basis beginning in early April and continuing through the first week in September. With the exception of the harvest period, there were an average of 2 visits during each crop stage as laid out in the manual which include: Dormant/Pre-Bloom, Bloom/Pre-Harvest, Harvest, and Post-Harvest. Actual scouting procedures varied with the crop stage and key pests of concern at the particular time. Four to five sites or stations were set up in each field at the first visit. Insects we reevaluated primarily by examination of plant parts, damage, or extraction from the canopy using a beating tray. Spider mites and predators we recounted on leaves in the field with the aid of a 10X hand lens. Cane and foliar diseases were usually rated using a scale of 0-5.Results from each visit were recorded on a single page report which then serves as a snapshot of pest incidence and activity. This information was then used by growers in their decision making process. Each field visit takes approximately one hour, followed by 5-10 minutes to record the findings.
Frequency of visits, insect and spider mite spray requirements, and disease development is presented in the attached table. Comments below address the key findings for each crop stage.
Dormant/Pre-Bloom
Initial visits illustrated the variation between fields regarding the incidence of overwintering stages of cane disease, in particular spur blight. These findings shed light on spray practices from the previous season and are useful in providing a rough disease rating which indicates carryover inoculum and potential for disease development in the current season. Oblique banded leafroller(OBLR)populations were very low in all fields and sprays were not necessary. Clay-colored weevils required spot treatment in one field only where they were detected at 8 weevils/10 trays and causing obvious damage to new growth from the ground to the wire. Western raspberry fruitworm were detected in two fields in late April using a beating tray. There are no action threshold levels established for this insect but presence of adults indicates potential for larval contamination of fruit. These two fields were treated in mid-May prior to bloom with diazinon. Spider mites were not a problem in any of the fields. Initial yellow rust (aecia)infection of fruiting laterals was detected in late April. This observation led to seemingly timely fungicide applications for yellow rust control in mid-May.
Bloom/Pre-Harvest
Spider mite populations were beginning to increase but miticides were not required in any of the fields. All fields were treated with Brigade as a cleanup spray in late June which provides both insect and spider mite control. A lower canopy spray was applied in one field to control rough strawberry root weevil (RSRW) in mid-June. RSRW were detected at 2 of 5 sites in this field at .5-1 weevil/tray. Blackvine weevils (BVW) were detected in two fields and at low density of not more than 1/10 trays at any site. BVW detections were more common in mid to late-June. All fields were treated with Brigade in late June as a cleanup spray. Secondary stage of yellow rust(uridia) was first detected in early June on fruiting laterals in all fields. Primocanes were essentially free of this disease. Spur blight infection of fruiting laterals and foliage intensified in late June. Foliar spur blight ratings in late June were highest in fields that had high inoculum ratings in early April. Spur blight infection was most common on fruiting laterals versus primocanes.
Harvest Period
Scouting during the harvest period was limited to 1 visit on one of the three farms only. This reduced scouting effort indicates the intense effort growers invest in harvest operations during this period. In addition, with the exception of certain fungicides, it is impractical for growers to apply most pesticides at this time due to pre-harvest interval requirements.
Scouting at the one farm in mid-July showed significantly reduced spider mite and weevil density following the late-June Brigade spray. OBLR trap catch ranged from 9-29 moths/trap since late June indicating that flight activity was highest in this early July period. Spur blight infection was still concentrated on fruiting laterals and no lesions were detected on primocanes at this time. Yellow rust incidence was still quite low.
Post-Harvest
Spider mites did not build to an economic level(25/leaflet) in any of the fields. The highest count was 12 spider mites/leaflet field average in late August with 2.4 predator mites/leaflet, a favorable ratio for spider mite suppression. There were no other insect problems during this period with the exception of aphids which were treated in one field primarily due to nuisance factor. Spur blight lesions on primocanes were observed in early August and the degree of infection in late August averaged 2 lesions/cane in one field and 1 lesion/cane in the other. The third field was pulled out in mid-August but primocane infection received a low rating in this field in early August. There was again a clear correlation between primocane infection levels and spring inoculum ratings for this disease. Yellow rust was present on both fruiting laterals and primocane foliage but disease incidence received low ratings in all fields. Botrytis primocane infection was moderate to high in 2 fields and disease incidence was heavier in fields with dense canopies.
Scouting results for diseases when compared to insects and mites cannot be used as easily to help make spray decisions, but may be useful in evaluating past practices and confirming the need for well-timed protectant fungicide applications.
Regular scouting is useful for determining the need for and timing of insect and mite sprays.
Pest pressure varies between raspberry fields, even in those under the same management.
With some training, growers are very capable of scouting their fields for key pests.
Scouting effort during the harvest period will be reduced compared to all other crop stages.
Spending an hour to scout a field 8-10 times during the season improves a grower's ability to make good pest management decisions and to identify pests accurately.
Incorporate this experience into the IPM scouting manual for raspberries.
Continue to develop accurate treatment thresholds for key pests.
Encourage mentors to share this scouting experience with other growers.
Investigate potential for disease forecasting models to fine-tune fungicide spray program.