John asks "Also from the previously mentioned ARS press release, something
called
spotted knapweed  (Centaurea maculosa or Centaurea biebersteinii) is
expanding incredibly fast in the western US and Canada (see below). Is
anybody aware if this is a plant that bees forage on?"

I believe this is a.k.a. Yellow Star Thistle.  It is a terrible weed because
virtually no livestock or wild animals will eat it and it crowds out natural
grasses.  It is a marvelous honey plant, blooming from mid-July to
mid-August and producing a very light honey that makes beautiful combs.

Lloyd
Lloyd Spear, Owner, Ross Rounds, Inc.  The finest in comb honey production.
www.rossrounds.com