Ok, so what I've determined with regards to the symphs is that most/all of the advice/research out there relating to them is done with relation to agricultural crops and large-scale gardening. Seeing as I have a small urban garden, management options that don't work on a large scale due to the labor involved may work for me on a small scale. So there are two goals here, 1) reducing the population to a manageable size that doesn't excessively stress the plants, 2) helping the plants evade/out-grow predation enough that they are not excessively stressed.
One thing mentioned on a lot of sites is using potato slices placed on the soil to bait them, then counting them as a means of determining your infestation level. One arm of my plan is to do this in my beds, but instead of just counting them, evicting them and drowning them. This is almost certainly one of those situations where for every 1 that I see/capture, there are at least a couple that I don't, but it's something.
So a couple days ago I put out my potato slice baits and covered them with party cups. Today I went in and uncovered them. Some were empty. Some had several symphs. Most had at least one, plus I was able to use a spade to grab a small handful of soil from under the potato as the others tried to flee and dump them all into a bucket. I also caught lots of immature symphs, so that's good, as well as a few slugs - another bonus. Interestingly, the potato baits I put in the spinach bed were some of the emptiest, but I dug up the now hopelessly stunted spinach seedlings and dumped all the soil around their bases, still heavily infested (indicating they prefer the root tips to potato slices), into the bucket, too. Drowned them all.
The white ones are the symphs:
Then I moved the potato baits to new locations in the beds and reset them. Will return to them on Friday to repeat the process.
Another thing I am considering is a rotation of the infested beds that looks like this:
Rest of this year: continue as planned, trying to nurse plants past serious danger.
Fall: Cover all beds in fava cover crop (not a plant they like)
Spring 2018: Plant all beds in potatoes (the only crop shown/thought to actively repel them), donate any I can't eat to food banks, I can still use the front yard beds for a small amount of other crops (assuming I don't find them there, too, but my early tests found none)
Late summer/fall 2018: Test for symph levels. If present in quantity, consider another fava rotation. If not, consider putting some beds into winter crops (broccoli, kale, collards, spinach, lettuce, etc).
One concern I have with this rotation plan though, is repelling them out of my vegetable beds may send them into neighboring growing areas, like my blueberries. Also, they're apparently long-lived and one season may not be enough to starve/repel them out enough to restart vegetables.
I also am going to have to target lower organic matter levels. The advice I've heard is only to add as much organic matter/compost as is the bare minimum needed to sustain soil microbiology. I've definitely been waaay above target on that over the years. One of my beds tested at 11% organic matter a couple years ago, which is great if you don't have symphs - bad if you do.
Things to consider. For now, I'm going to continue on (sans spinach) - everything except the spinach seems to be growing at a decent rate, although I can't help but wonder if they'd be doing even better if there were no symphs.
