Supporting the Good Guys

Floral resources to support parasitoids and predatory insects

In my imagination, the ideal Berry World looks a little like Geoff Langford’s berry cage.  It is home to our South Island strawberry variety trial, which we harvest for 6 months, along with a collection of raspberries, boysenberries, blackcurrants, cherries, plums, and the miscellaneous silverbeet that the chooks get for a treat.  Birds are excluded, and last year the only pest control measures that the strawberries required was an early season aphid spray and two botrytis sprays.  There was one cucumeris predatory mite release.  The spiders, praying mantids and parasitoids took care of the rest.

However it’s not commercial scale. And most aggravatingly, it’s “less than efficient” to harvest.

Wouldn’t it be great if there was a way to combine an efficient mechanized system with the kind of landscape that supports the good guys (useful parasitoids/predators)?

That magic combination is the goal of a recent project in Pukekohe vegetables, supported by Vegetables NZ, Onions NZ, and the Lighter Touch program.  At a recent Lighter Touch forum, Olivia Prouse (Cropping Services Ltd) spoke about the three types of “beneficials support systems” they have integrated into commercial vegetables.

1. Perennial native plants—these were carefully chosen to be low growing so as not to obstruct tractor movements, to provide flowers especially in winter, and to not host any of the vegetable pests.  In areas that didn’t need tractor clearance, shrubs were also used.  They were established as permanent plantings along side drains (weed control challenging!) and in “mobile homes,” moveable 1m³ forkliftable bins.
2. Mixed flowering annuals planted in strips among the vegetable crop (allysum, cornflowers, buckwheat, calendula, and marigolds)
3. Blocks of flowering cover crops, paddock-scale, on rotational vegetable land (buckwheat, phacelia, berseem clover, vetch and linseed)

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Overseas research has shown that the predators and tiny parasitoid insects will move about 15 meters into a crop from the flowering strip that has supported their growth, so this is taken into account when planning the spacing for the annual flowering strips.

Several vegetable crops were grown in with these systems, and the resulting impact on insecticide sprays are illustrated in the table below.

There’s an especially interesting story about that last lettuce crop.  It was a spring lettuce crop, which is at high risk for aphid infestation.  Scouting did show two aphid peaks, one which the natural enemies got on top of satisfactorily, and the other which was pending a spray when a neighboring cover crop was plowed under.  The resulting mass migration of predators out of the cover crop and into the lettuce ended up controlling the aphids on the lettuce without that spray being necessary.

One of the big takeaways I get from this study is that cultivating food for predators can work within a regular commercial production system, and that it’s not an all-or-nothing approach.  Predators and parasitoids reduced the need for insecticides but in many cases didn’t eliminate them, which is still a good outcome.  The other major service natural enemies can give us is to delay the onset of insecticide resistance.  Every aphid taken out by a parasitoid is not developing resistance to Transform, long may it last.

Olivia’s whole talk can be found at the Lighter Touch website, https://a-lighter-touch.co.nz/our-projects/biodiverse-planting/ along with a list of the plants used for the Pukekohe site.

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