Nothing will choke star thistle out once established. It does not like cultivated, wet ground so in all likelihood, it's the cultivation and irrigation that is keeping it at bay, not the rye. If you're going to cultivate and irrigate, you might as well choose a crop you WANT, it will most likely be just as effective as the rye.
What happens with cultivated ground though, is it takes over the edges where the irrigation is minimal, and slowly slips inward. You have to go out and pull it up by the root the second you see it on the edges. The corn gluten won't kill the roots and the second you hit a dry period, the star thistle will be back, though I'm sure running around putting corn gluten on the patches is a lot more fun than pulling them up by the roots.
If Rye and corn gluten would choke it out, the government wouldn't have spent hundreds of thousands of dollars testing Mediterranean flies to see if they could keep it at bay. The test was some what effective, it did reduce the star thistle in the test area by something like 25%, but it didn't eliminate it. That test was in the mid 90's in the Rogue Valley in Oregon, not sure what they've tested since then. You might check with your local agricultural exchange, they'd likely have the most current information on research and if the rye theory has ANY validity.
Cathy, who fought star thistle for 10 years and is so glad it doesn't like the high desert...yet
