Release of the Laboratory-reared Predator Mite, Amblyseius fallacis as a Biological Control Tactic for Spider Mites in raspberries.

June 1997 thru September 1997

Investigator/ Collaborators

WSU Nooksack Watershed IPM Project with several grower collaborators:

Brian Cieslar
Dick Nydam
Tena Ondeck
Randy Honcoop

Funded partially by USDA Farmer/Researcher SARE Grant, Clean Water Act, Section 319 with match from cooperating growers.

Project Description/How was it done?

Predator mites(PM) reared by Applied Bionomics Ltd. of Sidney, B.C., Canada were applied manually at four raspberry farms in Whatcom County in mid-June prior to pre-harvest clean-up insecticide sprays. Based on results from the previous season, release rates were increased from 7,000 PM/acre to evaluate two field release rates: 15,000 and 30,000 PM/acre. Material cost for these rates is $120- $240/ acre. These predators are reared on trifoliate bean leaves and applied by placing leaves within the canopy near the wire. They were evenly distributed throughout each treatment plot. Plot size ranged from .13 acres up to 1 acre in size. The lower release rate was used on two farms and the higher rate on the other two farms. On each farm, the downwind release site was compared to an upwind plot which was not treated with predator mites. Leaf samples were collected from these paired plots every two weeks from mid-June through the first week in September. Spider mite and predator mite mobile and egg stages were measured using a mite brushing machine and microscope. In most cases, a minimum of 2- 30 leaflet samples were taken from each plot. All plots were treated with Brigade(bifenthrin) within a week or so of the releases. This is a common practice to control insect harvest contaminants, particularly black vine weevil, on machine-picked raspberries. Some plots on two of the farms(Nydam, Honcoop)were also sprayed with Vendex to control high spider mite populations immediately after the PM release.

Results

Naturally occurring predator mites were present in all fields prior to PM release. Regardless of the rate of PM application, this tactic did not appear to offer any measurable benefits when compared to non release plots in terms of spider mite control. For the second year in a row, this work shows that predator mites in both the release and untreated sites are quite tolerant of Brigade applications. In addition, Brigade appeared to provide excellent control of spider mites even when spider mite populations were very high(>150/leaflet). It was difficult to isolate the effect of Vendex on either predator mites or spider mites, but appeared that the cool, wet conditions at the time applications were made limited its effectiveness and impacts.

Any problems or limitations?

Due to predator mite mobility it is difficult to determine the degree of contamination or migration between treated and untreated plots, particularly over the 3 month duration of the study.

What did we learn?

Spider mite population density varies from field to field.

Predator mites have some degree of tolerance to Brigade asa clean-up spray.

Spider mites did not rebuild in any of these fields to damaging levels(25/leaflet) by early September this year, probably due to cool conditions during harvest and impacts from Brigade and predator mites, which were quite numerous in late summer in all plots.

Field releases of A. fallacis even at these high rates do not significantly enhance biological control of spider mites.

Where do we go from here?

Conservation of naturally occurring predator mites rather than augmentative field releases appears to be a preferred strategy.

This may be realized through selection of least disruptive pesticides and better understanding of the influence of cultural practices on spider mite and predator mite dynamics.