In these cases, I would mark off two small patches, perhaps 10 by 10 feet each. I would use the first patch to be retreated with an ALS herbicide for the test. I would use the second patch as a check area for comparison to see if the first patch develops any injury symptoms. The tricky part will be measuring out the appropriate rate for some of these herbicides. Hand spraying may result in a slightly higher rate as well, but that should still be okay.
Resistant plants are usually resistant to many times the normal herbicide rate.
For common ragweed, I would use FirstRate to test for ALS resistance because it is the most active ALS herbicide on ragweed. For foxtail species, I would use Accent to test for ALS resistance in corn rather than Basis, Basis Gold, or Accent Gold since Accent has the greater activity on large foxtails. In soybeans, I would use Raptor over Pursuit for the same reason. It would be tempting to use Accent rather than Raptor for the test in soybeans because Accent has better activity on large foxtail than Raptor. However, the foxtail may not always be cross resistant to both sulfonylurea and imidazolinone herbicides even though both chemical families are ALS inhibitors.