Hiccups in biocontrol

Hiccups in biocontrol

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I might like to present a “Facebook version” of my predator-based insect control efforts, meaning only share the rosy successes.  However, this season I also had a failure, which has also given me a couple useful lessons.

I grow strawberry foundation stock, the mother plants for strawberry propagators.  The aim is to grow plants without pests and diseases, so they are grown in an insect-exclusion greenhouse and we’re very careful about our order of operations so we don’t track in pests, doing greenhouse work first, before field work.

The mother plants were started in early November, and by Christmas they were runnering nicely.  Around Christmas, I noticed spider mites on my Monterey bench—the hottest, driest corner of the greenhouse.  By the time I noticed them, the mild leaf stippling phase was past and we were on to full-on leaf bronzing, with webbing even starting.  I never noticed the early stages, so I can’t tell when it started—it felt like it exploded overnight.

I got a delivery of persimilis within a week, and they arrived alive and active.  I released them onto all the greenhouse benches, which translates to a crazy high rate.

Still, spider mite damage was spreading rapidly to the other front bench.  After two weeks I decided that, in the case of foundation stock, patience was not a virtue.  I sprayed the front two benches with abamectin, which worked quickly and thoroughly.  I’m guessing that the predator mites mopped up the spider mites which must have begun to spread to the other benches, because I didn’t see any more spider mites for the whole season.  Abamectin doesn’t take out eggs, so either the eggs hatched quickly enough in that hot environment that the new hatchlings were still killed by the abamectin residue, or the predators must have moved back in and cleaned them up.

My lessons:

• Scout more carefully, particularly the hot benches near the vent.
• Abamectin worked when needed. 
• The strategy of spraying just the hot spot and using predators on the rest worked well, as there have been no more spider mites for the past two months.

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