Ants in the Garden

This is a follow up to my recent post on radishes.  After applying the Bt, the ants (and whatever else) temporarily disappeared.  But they returned a few days later, with a vengeance.  Now, the ants have spread to the broccoli, which are planted adjacent to the radishes.

The radishes are pretty much totally decimated.  At least two of my broccoli plants keeled over today.

I'm baffled.  It really does appear that the ants are eating my radishes and broccoli.  The ants appear to to tunnel around the stem of the plant where it emerges from the soil, and underneath.  They tend to swarm there.  Several of them hang out motionlessly on the damaged part of the stem.  To my eyes, they sure look like they are eating the stem or sucking moisture from it.

Here is a video:

The damage to the stems does look a bit like cutworm damage.  It looks like something is shearing or shaving the stem at a particular place right where it sits below the soil.  The ants swarm all over that sheared section.  

Not to gross anyone out, but I was also working in the front yard garden today and found a huge swarm of ants.  I found them adjacent to my raspberry patch, where I just pulled out a tired old sage plant to make room for some new plantings.  I did not see any signs of plant damage but was shocked to see so many ants.

On the chance that it is caused by ants, I bought some diatomaceous earth today.  I also applied a second round of Bt again, in case it's cutworms.  For both, it takes a few days to work.  I will post an update in a few days. 

Here is the bottle of concentrated Bt.  I used a capful and mixed it with a half gallon of water.  I put that into a spray bottle and sprayed it on the radishes and broccoli to coat both the tops and bottoms of the leaves as well as possible.