Controlling Fruit Flies in Cane Berries

Long time lurker, first time poster here.

Location: I garden in a suburb of Los Angeles. We’re about zone 10a here, and usually have super hot summers (over 100F is normal and even hit 120F in 2018) and mild winters. This year has been exceptionally mild and wet though.

The berries: In February of 2018, I planted three berry crowns in my front yard garden, two thornless blackberries and one thornless boysenberry, in a 4ft by 12ft raised bed that runs from east to west on the south end of the garden. This bed gets full sun for about 12 hours a day. We installed a trellis the length of the bed made of wire mesh that’s about 6ft tall. We trained the berries up the trellis and it’s worked as a beautiful privacy screen—especially the boysenberries with their trailing habit. We also planted some strawberry crowns in the bed but those eventually got shaded out, though I occasionally see a bit of red strawberry through the mess of foliage. They’re usually buggy and get tossed to the chickens. I tucked in a small clump of onion chives on the eastern edge of the bed and they might be some of the happiest chives I’ve ever seen. Tons of flowers and foliage.

The boysenberries flowered and fruited first, and we got our first fruit in mid-May. We’ve had just about a months production and in that time we probably got over 10lbs from just the boysenberries. The blackberries are still flowering and setting fruit but haven’t ripened yet.

The problem: We’ve been noticing a lot of the boysenberries over the last two or so weeks had little worms in them. I’m pretty sure they’re fruit fly maggots. There are definitely fruit flies hanging out around the plants and the spider webs in the foliage have a healthy heaping of dead fruit flies in them.

Given that the blackberries are going to start ripening in the next couple of weeks, I’m really interested in protecting them from the fruit flies.

I’m thinking of cleaning up the bed by cutting back ALL of the boysenberry canes now (mid June) and letting the new growth for next years berries come up over the rest of the season. I’m also thinking of putting sticky traps in for the adults, but I have my doubts that it will be all that effective at controlling them.

I would like to avoid spraying insecticides if at all possible. There are a small army of mantises, lacewings, spiders, and even a lizard in the berry bed.

Do y’all think cutting the canes back/cleaning up and laying traps will work at controlling the fruit flies? Are there any other things that you think could work to control them?

And, since I haven’t been a berry gardener for very long, do you think cutting all the canes back now will do much harm for fruit production next year? The canes grew from February to about October/November last year, and leafed our again in late February this year. The growing season here is long but it does get obscenely hot and stays hot through September.

Thanks in advance for any advice, and if you’ve made it this far, thanks for taking the time to read my book.

tl;dr: Will cutting back spent canes and laying sticky traps help control fruit flies from infesting berries on canes that are just setting fruit now?

Fruit flies and lots of small flies are crazy for containers of fruit juice that they can't get out of.  

You can put small containers around with saran wrap over the top with a rubberband, and a few small slits in the saran wrap.   They like wine, beer, red wine, honey water, balsamic vinegar.  See what they prefer in your area.

A plastic container, milk jug, peanut jar, even a glass jar that can be recleaned, with saran wrap over the top with a couple slits.

Use several containers, one every 4 or 5 feet.  If they are in the sun, add water to them so they won't dry out.

Flies will go in but won't come out.

If the maggots are already on your berries, lightly sweep the vines/bushes with a soft broom, knock them to the ground.   They won't climb back up.

I wonder if you might not be experiencing this new invasion of vinegar flies I was reading about:

https://www.gardensalive.com/product/ybyg-worms-in-your-berries-there-is-a-new-pest-in-town

If so, fermenty traps done with enough intensity sound like a solution at your garden scale.

The other thing that's really important is to let the birds into your garden by keeping the dogs and cats out.   The meat-eating birds will go after any maggots or moth larvae before the berries are ripe, so until the berries start to ripen let the birds handle the bugs.

Then when the berries start to turn, cover them from the birds, and you can sweep, as above, or hand pick early in the morning.  But there should be fewer of them.

Sounds like spotted wing drosophila.  It's not quite in my area yet but it will be here soon.  I was talking to a nursery guy about it yesterday and he said there isn't any standard organic treatment for them.  I hope the traps work, I'll need something soon.  

I have heard that honeyberries are so early that they won't get the worms in them (in my climate).